Comment on
technical
terms of logic.
Gottlob-Frege-Posthumous-Writings
Still, throughout these writings, whether polished or not, we find that formidable clarity which distinguishes the work he published.
If one chose a motto for the title page of this volume, what could be more apt than Vauvernarques' 'La clarte est la bonne foi des philosophes'?
? ? IIISTORY OF THE FREGE NACHLAjJ AND THE BASIS FOR THIS EDITION1
When Frege died in Bad Kleinen on 26 July 1925, he left to his adopted son, 1he engineer Alfred Frege, a quantity of important scientific papers. 2 These mduded unpublished manuscripts of some length, almost all of which, however, were incomplete or in the form of drafts; notes and drafts of lcllers, as well as a large number of letters from his most important m:ademic correspondents. In a short note attached to his will dated 1 January 1925 Frege wrote concerning his bequest:
Dear Alfred,
Do not despise the pieces I have written. Even if all is not gold, there is gold in them. I believe there are things here which will one day be prized much more highly than they are now. Take care that nothing gets lost.
Your loving father. It is a large part of myself which I bequeath to you herewith.
The papers Frege left remained in Alfred Frege's keeping for more than a decade; on 26 November 1925 he handed over, amongst other things, a series of letters addressed to Frege (these included Russell's letters) to the t:hemist and historian of science Ludwig Darmstaedter for the latter's wllection in the Prussian State Library. He may have been moved to do this hy the fact that Darmstaedter had some time previous been in touch with Frege concerning the collection he was compiling, with the result that in 1919 he had received from Frege the piece printed on pp. 253-257. The manuscripts handed over to Darmstaedter in 1925 also included drafts of Frege's letters to Russell and rough copies of the hand-written sheets that Darmstaedter had received in 1919.
1 Cf. the account Der wissenschqftliche Nachlass von Gottlob Frege by H. Scholz and F. Bachmann in the Actes du congres international de philosophie scientifique, Paris 1935, Vol. VIII: Histoire de la logique et de la philosophie scientifique (published Paris 1936), pp. 24-30 (ed. ).
2 The papers here called 'scientific ['wissenschqftlich'] dealt of course with logic, philosophy and the foundations of mathematics. We have no equivalent in English for the German term: the noun ? Wissenschqft', which in the main text we have sometimes rendered by 'discipline', may be applied to any field of study, and not only to such as we should normally call 'scientific'. AI other places in this history we have used the word 'scientific' in the same convenient, if improper, sense (trans. ).
? X History ofthe Frege Nachlal3 and the Basisfor this Edition
In the thirties particular attention was devoted to Frege's writings by what was known at the time as 'Philosophisches Seminar B' [Department of Philosophy (B)] of the University of Munster; the head of department was H. Scholz and the department later became the well-known first German Institut fiir mathematische Logik und Grundlagenforschung [Institute for Mathematical Logic and Foundation Studies]. It was in this connection that Scholz tried to find out what had become of the writings Frege had left behind at his death [Frege's NachlajJ]. In 1935 he discovered where Frege's adopted son was living and entered into correspondence with him. Alfred Frege said that he was prepared to hand over Frege's NachlajJ to Scholz and his collaborators 'on the understanding', as Scholz and Bachmann write, 'that we should go over the papers and see whether they were suitable for publication and then deposit them in the library of the University of Munster in Westphalia'. Alfred Frege retained proprietary rights over Frege's NachlajJ, but on 26 July 1935 he made a written statement to the effect that in the event of his death Scholz should have the right of disposing
of the NachlajJ as he thought fit.
Scholz and Bachmann, his collaborator at that time, set to work
immediately and were able to report in detail on the Frege NachlajJ in their paper to the International Congress for scientific Philosophy which was held in Paris from 15 to 21 September 1935. In their address they issued a request that any letters of Frege's should be made available for the Frege archives in Munster. In the following years Scholz was able to get hold of a large number of Frege's letters, either originals or copies, for the Munster collection. In particular, Russell gave him the letters Frege had written to him.
Once Scholz had achieved an overall picture of the Frege NachlajJ, he decided to prepare a selection of shorter writings which was to include important unpublished papers and the correspondence with Russell. Three volumes of roughly 300 pages each were planned. Scholz was able to elicit the support of the Notgemeinschaft der deutschen Wissenschaft for this project. The group which then took up work on the edition included, besides Scholz and Bachmann, Dr Albrecht Becker and Marga Tietz. Where reference is made by the present editors to 'previous editors' of the NachlajJ, in nearly every case it is this group which is meant.
A letter written to Scholz on 2 March 1936 by the then Librarian of the University Library in Munster reveals that as early as 15 February 1936 Scholz had announced his intention of handing over to the Library, in accordance with the disposition made by Alfred Frege, the pieces entrusted to him. It was quite clear, however, that the NachlajJ remained in Department of Philosophy (B) right up to October 1943 and was only then deposited in the University Library because of the danger of its being destroyed by the air raids which were growing more and more frequent. However, this safety precaution pro~ed futile. The Frege NachlqjJ was destroyed by fire during the bombing of the city of Munster on 25 March 1945, in the course of which
? History ofthe Frege Nachlaf3 and the Basisfor this Edition XI
the University Library was badly hit. Scholz later wrote 'The work we were t? ngaged on has suffered immeasurably from the bombing. The whole of the original material, which after an initial shock to the foundations in October I<J43 had been handed over to the University Library for safe keeping, must he regarded as lost. After months of enquiries this information was communicated to me, a few weeks ago, by the present University I,ibrarian. ' Information subsequently obtained from Dr Heinrich Jansen, who had been in charge of the manuscript section of the University Library, confirmed the fact of the destruction of the NachlajJ and that it had happened on the date given above.
The Second World War not only led to the loss of the Frege manuscripts deposited at Munster; it brought the work on the three volume edition of 1:rcge's shorter writings to a virtual standstill. Nevertheless, in the course of preparing this edition typescript copies of most of the important pieces from the Nachla}J had been made. Scholz has managed to save the majority of these typescripts, either top copies or carbons, from being destroyed. It is these typescripts which have formed the basis of all subsequent projects for editing the NachlajJ.
Not long after the end of the war Scholz again took up his plan of preparing a three volume selection of Frege's writings. In 1947, with the support of the Forderergesellschaft of Munster University, he had copies made of most of the surviving pieces. The following extract from a letter he wrote gives one some idea of the stringencies of the post-war situation with which Scholz had to contend and the characteristic way in which he tried to cope with them:
The Rector,
Professor Dr E. Lehnartz
Dear Rector,
I request that, in the event of a supplementary delivery of coal becoming available for next winter, urgently required heating material should be allocated to mefor my study in Melcherstr. 26 II. This is far and away the largest room in our flat. The large library, which I was able to preserve, is kept there. The room is at least 25 metres square and is adjoined on one side by a glass verandah which inevitably acts as a cold-trap in winter. The room is heated by an efficient cylindrical stove.
The reason for my request:
I have to edit Gottlob Frege's 'Shorter Writings' for the occasion of the centenary of his birth in July of next year; these include the large corpus of writings which I unearthed, writings which this great German master, who pioneered work into the foundations of mathematics, left behind at his death. Until the outbreak of war this work was supported by the Notgemeinschaft der deutschen Wissenschqft. At that time the material existed in its entirety in carefully prepared transcripts divided into three
Munster, 23. 5. 47 Westring 17 I
? ? XII History ofthe Frege Nachlal3 and the Basisfor this Edition
volumes of around 300 pages each. The outbreak of war prevented this edition from appearing. With the exception of a series of carbon copies, I handed over this valuable material, along with the originals, to the University Library for safe keeping. Nevertheless it was all destroyed. I therefore have to have everything copied out once more from the surviving carbon copies,1 since I cannot possibly part with the only documents now remaining to me. A few weeks ago I was at last able to obtain a suitable person for the work of copying this material. She is paid out of the funds which have been placed at my disposal for this purpose by the Forderergesellschaft of the University acting under your chair- manship. I myself have made the large typewriter in my study available for this purpose. The work has to be done in this room since no other is available. It will, in any event, take up the whole of the winter. It cannot be postponed if the first volume at least is to come out in the course of next year. . . .
Yours sincerely,
Heinrich Scholz
The first volume did not, however, come out in 1948 or later. During the last decade of his life, serious illness made it increasingly difficult for Scholz to do sustained work. And so the edition at which he had laboured so doggedly since 1935 was still incomplete when he died at the end of 1956. Upon Scholz's retirement he was succeeded in the chair of Mathematical Logic and Foundation Studies by his pupil H. Hermes. And so, in accordance with the disposition made by Alfred Frege, Hermes, as Scholz's nominee, became responsible for preparing the edition ofFrege's Nachlaft.
The first impetus to renew work on this edition came in 1957 when Michael Dummett, the English Frege scholar, spent a period of study in the Institute for Mathematical Logic and Foundation Studies in Munster. Working from the notes Scholz had made in the thirties and the copies to be found in Scholz's Nachlaft, he made a preliminary conspectus of the material that Scholz had originally gathered together and the corpus that had survived. In addition, he tried to enlist the support of English trusts for the planned edition. Since this proved fruitless, nothing further came of this first initiative that succeeded Scholz's death. Nevertheless, Dummett's spade-work was an important help to the present editors, which they were thankful to receive. In a second effort to get things moving Hermes succeeded in persuading his two co-editors in 1961 to form a team, and this team has subsequently been engaged in preparing Frege's posthumous writings and his scientific correspondence for publication. In 1962 the Deutsche Forschungsgemeinschaft gave its support for the undertaking, with the result that work could be delegated to assistants. Among these assistants Dr Walburga Schwering, now Dr R6dding, and Herr Gottfried Gabriel have
1 Though, as we mentioned earlier, some of the top copies were found in Scholz's NachlqfJ (ed. ).
? History ofthe Frege Nachlaf3 and the Basis for this Edition Xlll
JJJadc such a substantial contribution to the completion of this volume that they are named on the title page.
l'hc first thing the editors decided was that they would depart from the plan that Scholz had followed so consistently. They gave up the idea of a ? . rkctcd edition, and decided upon a complete edition of Frege's extant ? ,rJL'ntitic writings and letters whether these were available as originals, mpics or transcripts. They made an exception only of drafts that had been written up and published. Since it was expected that a new impression or phlltomechanical reproduction-now completed-of all Frege's previously published writings would be published by the Wissenschaftlichen llut'hgesellschaft (Darmstadt) and the publishing house of G. Olms (Hildes- ll! 'im), the editors were able to exclude these. The editors therefore l? onlined themselves to preparing a complete edition in three volumes of <lottlob Frege's posthumous writings and scientific correspondence, the present first volume of which contains the whole of the extant Nachla}J, rxcluding the letters.
Scholz's death meant that the transcripts of the Frege Nachla}J that had ? . urvived became in turn part of a Nachla}J. Since in the post-war years Scholz had worked alone on his projected edition, all that was known about the history of the material, of how it was arranged and of how complete it was, was lost with him. As a result the editors had first to set to work and dassify anew the pieces from amongst Scholz's papers that he had managed to preserve.
lt is most unlikely that any scientific writings of Frege that Alfred Frege did not pass on to Scholz could have survived the war. Alfred Frege died in action on 15 June 1944 at Montesson near Paris. What became of his possessions is not known.
l'hc editors thank the Deutsche Forschungsgemeinschaft for their financial support in the preparation and printing of this volume, the University Libraries in Constance and Munster for their help in obtaining literature, the publishing house of Meiner for the care and patience it devoted, to such ! (nod effect, to this difficult text, Dr Lothar Kreiser (Leipzig) and Dr llcinrich Schepers (Munster) for valuable suggestions, and in particular those who collaborated in preparing this edition, amongst whom special mention must be made of Heinz Albert Veraart, as well as Gottfried Gabriel nnd Dr Walburga Rodding. Those others who have contributed from the thirties to the present day to the preparation and publication of the Frege Nachla}J with advice, information and assistance are too numerous to be listed here. To these, too, we wish to extend our warm gratitude.
H. Hermes F. Kambartel F. Kaulbach
? Logic 1 [between 1879 and 1891]
A. Introduction.
Essence, subject-matter.
Different from psychology, related to ethics. On method.
11 <'ontent of possible judgement. Negation. duplex negatio.
Combining contents of possible judgement into a new content. and, neither-nor and not etc.
Inferences.
( ? Analysis of a judgement. Concept, object.
Generality, condition, consequence. Or. Subordination of concepts. Existential judgements. (There is).
Elimination of auxiliary objects. Inferences involving particular judgements. Relation-concepts. Pairs.
I>. Ikfinitionofconcepts.
By means of characteristic marks. More complicated cases.
1'. . I>efinition of objects.
Indirect by means of concepts. Direct. Judgements in which something is recognized as the same again.
Improper existential judgements.
[A. Introduction]
121'. 1 Truth. Judging. Asserting.
Truth independent of our recognition.
Grounds that do-and grounds that do not-justify such recognition. The latter take place according to psychological laws, have no relation to truth.
1 In this piece (cf. Frege's footnote, p. 6) we clearly have a fragment of what was Intended as a textbook on logic.
! 'he footnote on p. 6 refers to the Begriffschrift {1879). In section B of the table 111' (on tents Frege uses the expression 'content of possible judgement'. From a letter 111 llusscrl dated 24. 5. 1891 it is clear that he had given up using this designation by lhr first half of 1891 at the latest. Therefore the present piece should be dated ! Jetween 1879 and 1891 (ed. ).
? ? 2 [2f. ] [3]
[4] [5]
[5f. ]
Logic
Superstitions about the weather have a basis in experience. Furnishing grounds of this kind is no proof.
Grounds that aflord a justification are often found in other truths. Inference. To establish laws of inference is the task of logic. Logic, like psychology, has for its subject-matter things that cannot be perceived by the senses. There is a sharp divide, however, marked by 'true'. Logic considers its objects in so far as they are true. What is true is true independently of the person who recognizes it to be true, and so is not a product of an inner process.
Comparison with ethics.
Comment on technical terms of logic. Rejection of psychological distinctions.
Isolating what is psychological, by consciously marking it off. Warning against confusing points of view and switching from one question to another. Danger lies in language. Translation possible? Yes, so far as the logical kernel is concerned. Value of learning languages for one's logical education.
[6] The formula-language of algebra: analysis of the logically complex. Reducing the laws of logic to one another.
The goal of scientific endeavour is truth. Inwardly to recognize something as true is to make a judgement, and to give expression to this judgement is to make an assertion.
What is true is true independently of our recognizing it as such. We can make mistakes. The grounds on which we make a judgement may justify our recognizing it as true; they may, however, merely give rise to our making a judgement, or make up our minds for us, without containing a justification for our judgement. Although each judgement we make is causally conditioned, it is nevertheless not the case that all these causes are grounds that afford a justification. There is an empirical tendency in philosophy which does not take sufficient heed of this distinction, and so, because our thinking takes its rise from experience, philosophy ends up by declaring all our knowledge to be empirical. The causes which merely give rise to acts of judgement do so in accordance with psychological laws; they are just as capable of leading to error as of leading to truth; theY. have no inherent relation to truth whatsoever; they know nothing of the opposition of true and false. The farmer whose fortunes are, for good or ill, bound up with the weather, seeks for means of determining what it will be like in advance. Little wonder that he attempts to link phases of the moon with variations in the weather and asks himself whether a full moon does not herald a change in the weather. If this appears to be confirmed-as may well be the case, since by and large the weather does not change abruptly and since it is not altogether easy to say whether the weather has changed-from that moment on he believes the weather is connected with
? Logic 3
1ht? moon, and this belief takes root because the cases that speak in its lnvour make a greater impression than those that do not and imprint themselves more firmly on his memory; and he thinks he now knows this 1mm experience. This is exactly what experience is in the case of the said t'mpirical tendency amongst philosophers. And so it is with every ~uperstition. Usually it is possible to make out the psychological causes. <'learly such an account of how men have come to hold something to be 1rue is no proof; and in science, too, the history of how a mathematical law wns discovered cannot take the place of the grounds that justify it. These will always be ahistorical; in other words, it will never depend on who first ~tnve them, what provided him with the incentive to follow up such a fruitful line of thought, when and where this occurred, and so forth.
Now the grounds which justify the recognition of a truth often reside in ol her truths which have already been recognized. But if there are any truths 1ccognized by us at all, this cannot be the only form that justification takes.
l'here must be judgements whose justification rests on something else, if 1hey stand in need ofjustification at all.
And this is where epistemology comes in. Logic is concerned only with 1hose grounds ofjudgement which are truths. To make a judgement because we are cognisant of other truths as providing a justification for it is known us inferring. There are laws governing this kind ofjustification, and to set up lhese laws of valid inference is the goal of logic.
The subject-matter of logic is therefore such as cannot be perceived by 1he senses and in this respect it compares with that of psychology and contrasts with that of the natural sciences. Instincts, ideas etc. are also neither visible nor tangible. All the same there is a sharp divide between 1hese disciplines, and it is marked by the word 'true'. Psychology is only concerned with truth in the way every other science is, in that its goal is to extend the domain of truths; but in the field it investigates it does not study the property 'true' as, in its field, physics focuses on the properties 'heavy', 'warm', etc. This is what logic does. It would not perhaps be beside the mark tu say that the laws of logic are nothing other than an unfolding of the content of the word 'true'. Anyone who has failed to grasp the meaning of this word-what marks it ofT from others-cannot attain to any clear idea uf what the task of logic is.
For psychology it is neither here nor there whether the products of the mental processes it studies may be called true. What is true is true independently of the person who recognizes it as true. What is true is therefore not a product of a mental process or inner act; for the product of one person's mind is not that of another's, however similar they may seem 10 be, just as the hunger of one person is not that of another or the eye of one person is not that of another, however close the resemblance may be. We do not directly observe the processes in the mind of another, only the
effects they have in the physical world. Strictly speaking, therefore, we can only form a superficial judgement of the similarity between mental
? 4 Logic
processes, since we are unable to unite the inner states experienced by different people in one consciousness and so compare them. If the content of the sentence 2 + 3 = 5 is exactly the same, in the strictest sense, for all those who recognize it to be true, this means that it is not a product of the mind of this person and a product of the mind of that person, but that it is grasped and recognized as true by both equally. Even if subjective elements are a necessary part and parcel of this grasping of a content, we shall not include them in what we call 'true'.
Logic has a closer affinity with ethics. The property 'good' has a significance for the latter analogous to that which the property 'true' has for the former. Although our actions and endeavours are all causally conditioned and explicable in psychological terms, they do not all deserve to be called good. Here, too, we can talk of justification, and here, too, this is not simply a matter of relating what actually took place or of showing that things had to happen as they did and not in any other way. Certainly we say 'tout comprendre, c'est tout pardonner', but we can only pardon what we consider not to be good.
What mak10s us so prone to embrace such erroneous views is that we define the task of logic as the investigation of the laws of thought, whilst understanding by this expression something on the same footing as the laws of nature: we understand them as laws in accordance with which thinking actually takes place and by whose means we could explain a single thought process in a particular person in a way analogous to that in which we explain, say, the movement of a planet by means of the law of gravity. The laws in accordance with which we actually draw inferences are not to be identified with laws of valid inference; otherwise we could never draw a wrong inference.
In these times when the theory of evolution is marching triumphantly through the sciences and the method of interpreting everything historically threatens to exceed its proper bounds, we must be prepared to face some strange and disconcerting questions. If man, like all other living creatures, has undergone a continuous process of evolution, have the laws of his thinking always been valid and will they always retain their validity? Will an inference that is valid now still be valid after thousands of years and was it already valid thousands of years ago? Clearly, the laws of how men do in fact think are being confounded here with the laws of valid inference. Let us take a somewhat closer look at this question. In the sense in which we speak of natural laws, psychological, mathematical or logical laws, it is, strictly speaking, impossible for laws to change at all. For such a law, expressed in full, must include mention of all relevant conditions, in which case it will hold independently of time and place. The law of inertia, for instance, claims to be valid for all times and regions of space. If it appeared not to be valid in, say, the neighbourhood of Sirius, we should assume that it had not been fully expressed, a condition having been overlooked which is satisfied here but not in the neighbourhood of Sirius. A genuine condition always contains
? Logic 5
something indefinite, and so, according to how this something is determined, 11 can assume the form of a true or false proposition. Thus if after some time 1he law of inertia no longer seemed to hold, this would be an indication that n further condition needed adding, a condition which had been satisfied up lo a certain date but not subsequently. The supposed change in the laws of
1hought would have to be interpreted in this way too; this could be no more thnn an apparent change and would be an indication that our knowledge of 1hese laws was incomplete. Now if by the laws of thought we understand the luws of logic, it is easy to see the absurdity of a condition relating, say, to the phosphorus content of our brains or to something else in human beings which is subject to change. In that case it would be quite possible that such a dtunge should have taken place in some people, but not in others, so that for Nomc people there would follow from certain truths the opposite to what would follow for others. This is utterly contrary to the nature of a law of In~tic, since it is contrary to the sense of the word 'true', which excludes any tciCrence to a knowing subject.
If, on the other hand, by the laws of thought we understand psychological luws, then we cannot rule out in advance the possibility that they should l'onlain mention of something that varies with time and place and, nl'wrdingly, that the process of thinking is different nowadays from what it wus 3000 years ago.
I,ogic, in common with every science, has its technical terms, words some uf which are also used outside the sciences, though not in quite the same ? ruse. It doesn't matter in the least if the meaning we fix on is not altogether In line with the everyday use of the word or it doesn't accord with its olymology; what does matter is that the word should be as appropriate a vehicle as possible for use in expressing the laws. Provided there is no loss of rl1uur, the more compendious the formulation of the whole system of laws I? . I he more felicitous is the apparatus of technical terms.
The task of logic being what it is, it follows that we must turn our backs 1111 unything that is not necessary for setting up the laws of inference. In pltrticular we must reject all distinctions in logic that are made from a purely p? ychological standpoint and have no bearing on inference. Similarly, in pure mechanics we don't distinguish substances according to their chemical properties, but speaks only of 'mass' and physical bodies, so that we don't h~tve, say, to establish a special law for each chemical substance in place of the one law of inertia. Therefore let us only distinguish where it serves our purpose. The so-called deepening of logic by psychology is nothing but a raiNiflcation of logic by psychology. In the form in which thinking naturally llovelops the logical and the psychological are bound up together. The task In hund is precisely that of isolating what is logical. This does not mean that
we want to banish any trace of what is psychological from thinking as it nMiurally takes place, which would be impossible; we only want to become ~twure of the logical justification for what we think. So the required 1epuration of the logical from the psychological is only a matter of
? ? 6 Logic
distinguishing in our minds between them. That is why we cannot give too many warnings against the danger of confusing points of view and switching from one question to another, a danger to which we are particularly exposed because we are accustomed to thinking in some language or other and because grammar, which has for speech a significance analogous to that which logic has for thought, is a mixture of the logical and the psychological. Otherwise all languages would necessarily have the same grammar. Can the same thought be expressed in different languages? Without a doubt, so far as the logical kernel is concerned; for otherwise it would not be possible for human beings to share a common intellectual life. But if we think of the kernel with the psychological husk added, a precise translation is impossible. Indeed we may go so far as to doubt whether the outer covering is the same for any two men. From this we can see the value of learning foreign languages for one's logical education; when we see that the same thought can be worded in different ways, our mind separates off the husk from the kernel, though, in any given language, it appears as a natural and integral part of it. This is how the differences between languages can facilitate our grasp of what is logical. But still the difficulties are not wholly removed in this way and our logicians still keep dragging in a number of things which are really of no logical concern, though they belong to the grammar of languages akin to our own, if not to others. For this reason it is useful to be acquainted also with a means of expression of a quite different kind, such as we have, for instance, in the formula-language of algebra. *
But even when we have completely isolated what is logical in some form or phrase from the vernacular or in some combination of words, our task is still not complete. What we obtain will generally turn out to be complex; we have to analyse this, for here as elsewhere we only attain full insight by pressing forwards until we arrive at what is absolutely simple. In this respect, too, logic, because of its attachment to language and grammar, has fallen short in a number of ways. The laws of logic are themselves truths and here again there arises the question how a judgement is justified. If it is not justified in terms of other truths, then logic doesn't need to bother itself with it any further. If, on the other hand, a law of logic can be reduced to other laws by a process of inference, then it is evidently the task of logic to carry out this reduction; for it is only by doing this that we can reach a vantage point from which we can take a conspectus of the laws of logic, and not count as many a law that is one and the same.
To sum up briefly, it is the business of the logician to conduct an unceasing struggle against psychology and those parts of language and
*In this connection mention might also be made of my concept-script. I would not be in a position to write this work on logic without benefit of my earlier endeavours to devise a concept-script.
? Logic 7
l(rammar which fail to give untrammelled expression to what is logical. He does not have to answer the question: how does thinking normally take place in human beings? What course does it naturally follow in the human 111ind? What is natural to one person may well be unnatural to another. To . ~ee this we need look no further than to the great difference between l(rammars. There is no reproach the logician need fear less than the 1eproach that his way of formulating things is unnatural, that the actual 11rocess of thinking follows a different course. If you aim to teach a beginner the rudiments of mathematics in as logically rigorous a form as possible, he will, unless he is quite exceptional, find this very unnatural, and for the very 1enson that such a degree of rigour is employed. As a result, he will understand what he is taught either not at all or only imperfectly. Therefore, oue needs to temper the rigour of one's approach in the early stages, and o11ly as one advances try by degrees to arouse a need for it. Even in utathematics we find that the most rigorous work always belongs to the lntcst stages in the history of the subject. If we were to heed those who ? ? h. iect that logic is unnatural, we would run the risk of becoming embroiled 111 interminable disputes about what is natural, disputes which are quite 1111:apable of being resolved within the province of logic, and which therefore lluvc no place in logic at all. Perhaps definitive answers are simply not to be hud, or cannot be given until we have observed primitive peoples and made u scientific study of languages.
[B. ] Content of possible judgement
Inwardly to recognize something as true is to make a judgement. Thus an instance of a content of possible judgement is the content of the equation 2 1 3 ~ 5. As we have seen, such a content is not the result of an inner pro- cess or the product of a mental act which men perform, but something objective: that is to say, it is something that is exactly the same for all mtional beings, for all who are capable of grasping it, just as the sun, say, is 11ornething objective. But isn't the sun perhaps for some people a beneficent or maleficent deity, for others a shining disk hurled into the heavens from the oust and rolling back down again towards the west, and for yet others an Immense, spherical white-hot body enveloped by a cloud of incandescent I&IINcs'! No. To some it may seem one thing, to others another; it is what it is.
A judgement is often preceded by questions. A mathematician will formulate a theorem to himself before he can prove it. A physicist will 11. a:cpt a law as an hypothesis in order to test it by experience. We grasp the l)unlcnt of a truth before we recognize it as true, but we grasp not only this; we grasp the opposite as well. In asking a question we are poised between opposite sentences. Although it is usually only one side that is expressed when we speak,? the other is still always implied; for the sense of the
? Here, of course, we are referring only to sentence-questions, not to wurd questions.
? 8 Logic
question remains the same if we add 'or not? '. It is this very fact which makes possible such verbal economy. Now whatever can thus be posed in a question, we wish to call a content of possible judgement. Therefore the content of any truth is 'a content of possible judgement', but so too is the opposite content. This opposition or conflict is such that we automatically reject one limb as false when we accept the other as true, and conversely. The rejection of the one and the acceptance of the other are one and the same.
? Boole's logical Calculus and the Concept-script1 [1880/81]
In his writings, Leibniz threw out such a profusion of seeds of ideas that in IIus respect he is virtually in a class of his own. A number of these seeds wrrc developed and brought to fruition within his own lifetime and with his 11tllaboration, yet more were forgotten, then later rediscovered and drvcloped further. This justifies the expectation that a great deal in his work lhul is now to all appearance dead and buried will one day enjoy a rr,urrcction. As part of this, I count an idea which Leibniz clung to lluuughout his life with the utmost tenacity, the idea of a lingua l'haracterica, an idea which in his mind had the closest possible links with lhnl of a calculus ratiocinatur. That it made it possible to perform a type of ru111putation, it was precisely this fact that Leibniz saw as a principal ndvanlage of a script which compounded a concept out of its constituents rnl her than a word out of its sounds, and of all hopes he cherished in this muller, we can even today share this one with complete confidence. I will IJlrulc just the following from the relevant passages:
'Si daretur vel lingua quaedam exacta, vel genus scripturae vere philosophiae, . . . omnia quae ex datis ratione assequi, inveniri possent l. fUodam genere calculi, perinde ac resolvuntur problemata arithmetica aut jcomctrica. '*
? I>c Scientia universali seu calculo philosophico.
1 In 188 I, this article was submitted by Frege in turn to the Zeitschrift fiir Matlrematik und Physik, the Mathematischen Annalen and the Zeitschrift fiir l'lr/lu. wphie und philosophisehe Kritik, but was in every case rejected by the editors. lllluully remained unpublished.
l'rom the report of H. Scholz and F. Bachmann: Der wissenschaftliche Nachlass r? mt {,'o/1/ob Frege (Paris 1936) we learn that the lost original was 'a manuscript rrrJlnrcd for publication of 103 closely written sides of quarto'. Scholz and lt11chmann mention besides that Frege also submitted the manuscript to R. Avenarius for the Vierteljahrsschrift fii. r wissenschaftliche Philosophie. However it 11uuld be that what Frege submitted to Avenarius was the essay published in this v11lumc on pp. 47 IT. 'Boole's logical Formula-language and my Concept-Script', llnce Avenarius in his letter to Frege of 20/4/1882 cites the title of the manuscript rtlurncd by him as 'Boole's logical Formula-Language'.
The article can scarcely have been composed before 1880, the year in which the rtview by Schroder mentioned on p. 11 appeared. A great number of the reflections
? ? ? 10 Boole's logical Calculus and the Concept-script
Among the various sorties Leibniz made upon his goal, the beginnings of a symbolic logic come closest to what seems to be indicated by the phrase 'calculus ratiocinatur'. They are to be found in the essays:
Non inelegans specimen demonstrandi in abstractis and Addenda ad specimen calculi universalis
In these Leibniz stuck very close to language. Just as the words we use for the attributes of a thing follow one another, so he simply juxtaposes the letters corresponding to properties in order to express the formation of a concept. If, for instance, A means right-angled, B isosceles, C triangle, then Leibniz represents right-angled isosceles triangle by ABC. He uses a sign for identity, oo, and the sign + with the definition:
'A +Boo L significat A inesse ipsi L'.
This seems to coincide with the meaning recent logicians have given this sign, according to which A + B represents the class of individuals which belong to A or to B or to both. Since I am passing over less important details, the only other fact I will mention is that Leibniz allows the words 'non' and 'ens' to occur in his formulae. In this project he surely has the lingua characterica in mind, even though he made no express connection with the attempts he made to represent a content.
This way of setting up a formal logic seems to suggest itself naturally. At any rate recent German and English logicians have arrived at the same conception quite independently of Leibniz, though, as far as I know, in doing so they do not have a general characteristic in mind. However much Boolean logic* may stand out as a systematic working out of the fragmen- tary hints in Leibniz, it only goes beyond him in one point of fundamental importance-in the way it reduces hypothetical and disjunctive judgements to categorical. ? ? The Leibnizian 'ens' is left out.
In a short monograph,? ? ?
? ? IIISTORY OF THE FREGE NACHLAjJ AND THE BASIS FOR THIS EDITION1
When Frege died in Bad Kleinen on 26 July 1925, he left to his adopted son, 1he engineer Alfred Frege, a quantity of important scientific papers. 2 These mduded unpublished manuscripts of some length, almost all of which, however, were incomplete or in the form of drafts; notes and drafts of lcllers, as well as a large number of letters from his most important m:ademic correspondents. In a short note attached to his will dated 1 January 1925 Frege wrote concerning his bequest:
Dear Alfred,
Do not despise the pieces I have written. Even if all is not gold, there is gold in them. I believe there are things here which will one day be prized much more highly than they are now. Take care that nothing gets lost.
Your loving father. It is a large part of myself which I bequeath to you herewith.
The papers Frege left remained in Alfred Frege's keeping for more than a decade; on 26 November 1925 he handed over, amongst other things, a series of letters addressed to Frege (these included Russell's letters) to the t:hemist and historian of science Ludwig Darmstaedter for the latter's wllection in the Prussian State Library. He may have been moved to do this hy the fact that Darmstaedter had some time previous been in touch with Frege concerning the collection he was compiling, with the result that in 1919 he had received from Frege the piece printed on pp. 253-257. The manuscripts handed over to Darmstaedter in 1925 also included drafts of Frege's letters to Russell and rough copies of the hand-written sheets that Darmstaedter had received in 1919.
1 Cf. the account Der wissenschqftliche Nachlass von Gottlob Frege by H. Scholz and F. Bachmann in the Actes du congres international de philosophie scientifique, Paris 1935, Vol. VIII: Histoire de la logique et de la philosophie scientifique (published Paris 1936), pp. 24-30 (ed. ).
2 The papers here called 'scientific ['wissenschqftlich'] dealt of course with logic, philosophy and the foundations of mathematics. We have no equivalent in English for the German term: the noun ? Wissenschqft', which in the main text we have sometimes rendered by 'discipline', may be applied to any field of study, and not only to such as we should normally call 'scientific'. AI other places in this history we have used the word 'scientific' in the same convenient, if improper, sense (trans. ).
? X History ofthe Frege Nachlal3 and the Basisfor this Edition
In the thirties particular attention was devoted to Frege's writings by what was known at the time as 'Philosophisches Seminar B' [Department of Philosophy (B)] of the University of Munster; the head of department was H. Scholz and the department later became the well-known first German Institut fiir mathematische Logik und Grundlagenforschung [Institute for Mathematical Logic and Foundation Studies]. It was in this connection that Scholz tried to find out what had become of the writings Frege had left behind at his death [Frege's NachlajJ]. In 1935 he discovered where Frege's adopted son was living and entered into correspondence with him. Alfred Frege said that he was prepared to hand over Frege's NachlajJ to Scholz and his collaborators 'on the understanding', as Scholz and Bachmann write, 'that we should go over the papers and see whether they were suitable for publication and then deposit them in the library of the University of Munster in Westphalia'. Alfred Frege retained proprietary rights over Frege's NachlajJ, but on 26 July 1935 he made a written statement to the effect that in the event of his death Scholz should have the right of disposing
of the NachlajJ as he thought fit.
Scholz and Bachmann, his collaborator at that time, set to work
immediately and were able to report in detail on the Frege NachlajJ in their paper to the International Congress for scientific Philosophy which was held in Paris from 15 to 21 September 1935. In their address they issued a request that any letters of Frege's should be made available for the Frege archives in Munster. In the following years Scholz was able to get hold of a large number of Frege's letters, either originals or copies, for the Munster collection. In particular, Russell gave him the letters Frege had written to him.
Once Scholz had achieved an overall picture of the Frege NachlajJ, he decided to prepare a selection of shorter writings which was to include important unpublished papers and the correspondence with Russell. Three volumes of roughly 300 pages each were planned. Scholz was able to elicit the support of the Notgemeinschaft der deutschen Wissenschaft for this project. The group which then took up work on the edition included, besides Scholz and Bachmann, Dr Albrecht Becker and Marga Tietz. Where reference is made by the present editors to 'previous editors' of the NachlajJ, in nearly every case it is this group which is meant.
A letter written to Scholz on 2 March 1936 by the then Librarian of the University Library in Munster reveals that as early as 15 February 1936 Scholz had announced his intention of handing over to the Library, in accordance with the disposition made by Alfred Frege, the pieces entrusted to him. It was quite clear, however, that the NachlajJ remained in Department of Philosophy (B) right up to October 1943 and was only then deposited in the University Library because of the danger of its being destroyed by the air raids which were growing more and more frequent. However, this safety precaution pro~ed futile. The Frege NachlqjJ was destroyed by fire during the bombing of the city of Munster on 25 March 1945, in the course of which
? History ofthe Frege Nachlaf3 and the Basisfor this Edition XI
the University Library was badly hit. Scholz later wrote 'The work we were t? ngaged on has suffered immeasurably from the bombing. The whole of the original material, which after an initial shock to the foundations in October I<J43 had been handed over to the University Library for safe keeping, must he regarded as lost. After months of enquiries this information was communicated to me, a few weeks ago, by the present University I,ibrarian. ' Information subsequently obtained from Dr Heinrich Jansen, who had been in charge of the manuscript section of the University Library, confirmed the fact of the destruction of the NachlajJ and that it had happened on the date given above.
The Second World War not only led to the loss of the Frege manuscripts deposited at Munster; it brought the work on the three volume edition of 1:rcge's shorter writings to a virtual standstill. Nevertheless, in the course of preparing this edition typescript copies of most of the important pieces from the Nachla}J had been made. Scholz has managed to save the majority of these typescripts, either top copies or carbons, from being destroyed. It is these typescripts which have formed the basis of all subsequent projects for editing the NachlajJ.
Not long after the end of the war Scholz again took up his plan of preparing a three volume selection of Frege's writings. In 1947, with the support of the Forderergesellschaft of Munster University, he had copies made of most of the surviving pieces. The following extract from a letter he wrote gives one some idea of the stringencies of the post-war situation with which Scholz had to contend and the characteristic way in which he tried to cope with them:
The Rector,
Professor Dr E. Lehnartz
Dear Rector,
I request that, in the event of a supplementary delivery of coal becoming available for next winter, urgently required heating material should be allocated to mefor my study in Melcherstr. 26 II. This is far and away the largest room in our flat. The large library, which I was able to preserve, is kept there. The room is at least 25 metres square and is adjoined on one side by a glass verandah which inevitably acts as a cold-trap in winter. The room is heated by an efficient cylindrical stove.
The reason for my request:
I have to edit Gottlob Frege's 'Shorter Writings' for the occasion of the centenary of his birth in July of next year; these include the large corpus of writings which I unearthed, writings which this great German master, who pioneered work into the foundations of mathematics, left behind at his death. Until the outbreak of war this work was supported by the Notgemeinschaft der deutschen Wissenschqft. At that time the material existed in its entirety in carefully prepared transcripts divided into three
Munster, 23. 5. 47 Westring 17 I
? ? XII History ofthe Frege Nachlal3 and the Basisfor this Edition
volumes of around 300 pages each. The outbreak of war prevented this edition from appearing. With the exception of a series of carbon copies, I handed over this valuable material, along with the originals, to the University Library for safe keeping. Nevertheless it was all destroyed. I therefore have to have everything copied out once more from the surviving carbon copies,1 since I cannot possibly part with the only documents now remaining to me. A few weeks ago I was at last able to obtain a suitable person for the work of copying this material. She is paid out of the funds which have been placed at my disposal for this purpose by the Forderergesellschaft of the University acting under your chair- manship. I myself have made the large typewriter in my study available for this purpose. The work has to be done in this room since no other is available. It will, in any event, take up the whole of the winter. It cannot be postponed if the first volume at least is to come out in the course of next year. . . .
Yours sincerely,
Heinrich Scholz
The first volume did not, however, come out in 1948 or later. During the last decade of his life, serious illness made it increasingly difficult for Scholz to do sustained work. And so the edition at which he had laboured so doggedly since 1935 was still incomplete when he died at the end of 1956. Upon Scholz's retirement he was succeeded in the chair of Mathematical Logic and Foundation Studies by his pupil H. Hermes. And so, in accordance with the disposition made by Alfred Frege, Hermes, as Scholz's nominee, became responsible for preparing the edition ofFrege's Nachlaft.
The first impetus to renew work on this edition came in 1957 when Michael Dummett, the English Frege scholar, spent a period of study in the Institute for Mathematical Logic and Foundation Studies in Munster. Working from the notes Scholz had made in the thirties and the copies to be found in Scholz's Nachlaft, he made a preliminary conspectus of the material that Scholz had originally gathered together and the corpus that had survived. In addition, he tried to enlist the support of English trusts for the planned edition. Since this proved fruitless, nothing further came of this first initiative that succeeded Scholz's death. Nevertheless, Dummett's spade-work was an important help to the present editors, which they were thankful to receive. In a second effort to get things moving Hermes succeeded in persuading his two co-editors in 1961 to form a team, and this team has subsequently been engaged in preparing Frege's posthumous writings and his scientific correspondence for publication. In 1962 the Deutsche Forschungsgemeinschaft gave its support for the undertaking, with the result that work could be delegated to assistants. Among these assistants Dr Walburga Schwering, now Dr R6dding, and Herr Gottfried Gabriel have
1 Though, as we mentioned earlier, some of the top copies were found in Scholz's NachlqfJ (ed. ).
? History ofthe Frege Nachlaf3 and the Basis for this Edition Xlll
JJJadc such a substantial contribution to the completion of this volume that they are named on the title page.
l'hc first thing the editors decided was that they would depart from the plan that Scholz had followed so consistently. They gave up the idea of a ? . rkctcd edition, and decided upon a complete edition of Frege's extant ? ,rJL'ntitic writings and letters whether these were available as originals, mpics or transcripts. They made an exception only of drafts that had been written up and published. Since it was expected that a new impression or phlltomechanical reproduction-now completed-of all Frege's previously published writings would be published by the Wissenschaftlichen llut'hgesellschaft (Darmstadt) and the publishing house of G. Olms (Hildes- ll! 'im), the editors were able to exclude these. The editors therefore l? onlined themselves to preparing a complete edition in three volumes of <lottlob Frege's posthumous writings and scientific correspondence, the present first volume of which contains the whole of the extant Nachla}J, rxcluding the letters.
Scholz's death meant that the transcripts of the Frege Nachla}J that had ? . urvived became in turn part of a Nachla}J. Since in the post-war years Scholz had worked alone on his projected edition, all that was known about the history of the material, of how it was arranged and of how complete it was, was lost with him. As a result the editors had first to set to work and dassify anew the pieces from amongst Scholz's papers that he had managed to preserve.
lt is most unlikely that any scientific writings of Frege that Alfred Frege did not pass on to Scholz could have survived the war. Alfred Frege died in action on 15 June 1944 at Montesson near Paris. What became of his possessions is not known.
l'hc editors thank the Deutsche Forschungsgemeinschaft for their financial support in the preparation and printing of this volume, the University Libraries in Constance and Munster for their help in obtaining literature, the publishing house of Meiner for the care and patience it devoted, to such ! (nod effect, to this difficult text, Dr Lothar Kreiser (Leipzig) and Dr llcinrich Schepers (Munster) for valuable suggestions, and in particular those who collaborated in preparing this edition, amongst whom special mention must be made of Heinz Albert Veraart, as well as Gottfried Gabriel nnd Dr Walburga Rodding. Those others who have contributed from the thirties to the present day to the preparation and publication of the Frege Nachla}J with advice, information and assistance are too numerous to be listed here. To these, too, we wish to extend our warm gratitude.
H. Hermes F. Kambartel F. Kaulbach
? Logic 1 [between 1879 and 1891]
A. Introduction.
Essence, subject-matter.
Different from psychology, related to ethics. On method.
11 <'ontent of possible judgement. Negation. duplex negatio.
Combining contents of possible judgement into a new content. and, neither-nor and not etc.
Inferences.
( ? Analysis of a judgement. Concept, object.
Generality, condition, consequence. Or. Subordination of concepts. Existential judgements. (There is).
Elimination of auxiliary objects. Inferences involving particular judgements. Relation-concepts. Pairs.
I>. Ikfinitionofconcepts.
By means of characteristic marks. More complicated cases.
1'. . I>efinition of objects.
Indirect by means of concepts. Direct. Judgements in which something is recognized as the same again.
Improper existential judgements.
[A. Introduction]
121'. 1 Truth. Judging. Asserting.
Truth independent of our recognition.
Grounds that do-and grounds that do not-justify such recognition. The latter take place according to psychological laws, have no relation to truth.
1 In this piece (cf. Frege's footnote, p. 6) we clearly have a fragment of what was Intended as a textbook on logic.
! 'he footnote on p. 6 refers to the Begriffschrift {1879). In section B of the table 111' (on tents Frege uses the expression 'content of possible judgement'. From a letter 111 llusscrl dated 24. 5. 1891 it is clear that he had given up using this designation by lhr first half of 1891 at the latest. Therefore the present piece should be dated ! Jetween 1879 and 1891 (ed. ).
? ? 2 [2f. ] [3]
[4] [5]
[5f. ]
Logic
Superstitions about the weather have a basis in experience. Furnishing grounds of this kind is no proof.
Grounds that aflord a justification are often found in other truths. Inference. To establish laws of inference is the task of logic. Logic, like psychology, has for its subject-matter things that cannot be perceived by the senses. There is a sharp divide, however, marked by 'true'. Logic considers its objects in so far as they are true. What is true is true independently of the person who recognizes it to be true, and so is not a product of an inner process.
Comparison with ethics.
Comment on technical terms of logic. Rejection of psychological distinctions.
Isolating what is psychological, by consciously marking it off. Warning against confusing points of view and switching from one question to another. Danger lies in language. Translation possible? Yes, so far as the logical kernel is concerned. Value of learning languages for one's logical education.
[6] The formula-language of algebra: analysis of the logically complex. Reducing the laws of logic to one another.
The goal of scientific endeavour is truth. Inwardly to recognize something as true is to make a judgement, and to give expression to this judgement is to make an assertion.
What is true is true independently of our recognizing it as such. We can make mistakes. The grounds on which we make a judgement may justify our recognizing it as true; they may, however, merely give rise to our making a judgement, or make up our minds for us, without containing a justification for our judgement. Although each judgement we make is causally conditioned, it is nevertheless not the case that all these causes are grounds that afford a justification. There is an empirical tendency in philosophy which does not take sufficient heed of this distinction, and so, because our thinking takes its rise from experience, philosophy ends up by declaring all our knowledge to be empirical. The causes which merely give rise to acts of judgement do so in accordance with psychological laws; they are just as capable of leading to error as of leading to truth; theY. have no inherent relation to truth whatsoever; they know nothing of the opposition of true and false. The farmer whose fortunes are, for good or ill, bound up with the weather, seeks for means of determining what it will be like in advance. Little wonder that he attempts to link phases of the moon with variations in the weather and asks himself whether a full moon does not herald a change in the weather. If this appears to be confirmed-as may well be the case, since by and large the weather does not change abruptly and since it is not altogether easy to say whether the weather has changed-from that moment on he believes the weather is connected with
? Logic 3
1ht? moon, and this belief takes root because the cases that speak in its lnvour make a greater impression than those that do not and imprint themselves more firmly on his memory; and he thinks he now knows this 1mm experience. This is exactly what experience is in the case of the said t'mpirical tendency amongst philosophers. And so it is with every ~uperstition. Usually it is possible to make out the psychological causes. <'learly such an account of how men have come to hold something to be 1rue is no proof; and in science, too, the history of how a mathematical law wns discovered cannot take the place of the grounds that justify it. These will always be ahistorical; in other words, it will never depend on who first ~tnve them, what provided him with the incentive to follow up such a fruitful line of thought, when and where this occurred, and so forth.
Now the grounds which justify the recognition of a truth often reside in ol her truths which have already been recognized. But if there are any truths 1ccognized by us at all, this cannot be the only form that justification takes.
l'here must be judgements whose justification rests on something else, if 1hey stand in need ofjustification at all.
And this is where epistemology comes in. Logic is concerned only with 1hose grounds ofjudgement which are truths. To make a judgement because we are cognisant of other truths as providing a justification for it is known us inferring. There are laws governing this kind ofjustification, and to set up lhese laws of valid inference is the goal of logic.
The subject-matter of logic is therefore such as cannot be perceived by 1he senses and in this respect it compares with that of psychology and contrasts with that of the natural sciences. Instincts, ideas etc. are also neither visible nor tangible. All the same there is a sharp divide between 1hese disciplines, and it is marked by the word 'true'. Psychology is only concerned with truth in the way every other science is, in that its goal is to extend the domain of truths; but in the field it investigates it does not study the property 'true' as, in its field, physics focuses on the properties 'heavy', 'warm', etc. This is what logic does. It would not perhaps be beside the mark tu say that the laws of logic are nothing other than an unfolding of the content of the word 'true'. Anyone who has failed to grasp the meaning of this word-what marks it ofT from others-cannot attain to any clear idea uf what the task of logic is.
For psychology it is neither here nor there whether the products of the mental processes it studies may be called true. What is true is true independently of the person who recognizes it as true. What is true is therefore not a product of a mental process or inner act; for the product of one person's mind is not that of another's, however similar they may seem 10 be, just as the hunger of one person is not that of another or the eye of one person is not that of another, however close the resemblance may be. We do not directly observe the processes in the mind of another, only the
effects they have in the physical world. Strictly speaking, therefore, we can only form a superficial judgement of the similarity between mental
? 4 Logic
processes, since we are unable to unite the inner states experienced by different people in one consciousness and so compare them. If the content of the sentence 2 + 3 = 5 is exactly the same, in the strictest sense, for all those who recognize it to be true, this means that it is not a product of the mind of this person and a product of the mind of that person, but that it is grasped and recognized as true by both equally. Even if subjective elements are a necessary part and parcel of this grasping of a content, we shall not include them in what we call 'true'.
Logic has a closer affinity with ethics. The property 'good' has a significance for the latter analogous to that which the property 'true' has for the former. Although our actions and endeavours are all causally conditioned and explicable in psychological terms, they do not all deserve to be called good. Here, too, we can talk of justification, and here, too, this is not simply a matter of relating what actually took place or of showing that things had to happen as they did and not in any other way. Certainly we say 'tout comprendre, c'est tout pardonner', but we can only pardon what we consider not to be good.
What mak10s us so prone to embrace such erroneous views is that we define the task of logic as the investigation of the laws of thought, whilst understanding by this expression something on the same footing as the laws of nature: we understand them as laws in accordance with which thinking actually takes place and by whose means we could explain a single thought process in a particular person in a way analogous to that in which we explain, say, the movement of a planet by means of the law of gravity. The laws in accordance with which we actually draw inferences are not to be identified with laws of valid inference; otherwise we could never draw a wrong inference.
In these times when the theory of evolution is marching triumphantly through the sciences and the method of interpreting everything historically threatens to exceed its proper bounds, we must be prepared to face some strange and disconcerting questions. If man, like all other living creatures, has undergone a continuous process of evolution, have the laws of his thinking always been valid and will they always retain their validity? Will an inference that is valid now still be valid after thousands of years and was it already valid thousands of years ago? Clearly, the laws of how men do in fact think are being confounded here with the laws of valid inference. Let us take a somewhat closer look at this question. In the sense in which we speak of natural laws, psychological, mathematical or logical laws, it is, strictly speaking, impossible for laws to change at all. For such a law, expressed in full, must include mention of all relevant conditions, in which case it will hold independently of time and place. The law of inertia, for instance, claims to be valid for all times and regions of space. If it appeared not to be valid in, say, the neighbourhood of Sirius, we should assume that it had not been fully expressed, a condition having been overlooked which is satisfied here but not in the neighbourhood of Sirius. A genuine condition always contains
? Logic 5
something indefinite, and so, according to how this something is determined, 11 can assume the form of a true or false proposition. Thus if after some time 1he law of inertia no longer seemed to hold, this would be an indication that n further condition needed adding, a condition which had been satisfied up lo a certain date but not subsequently. The supposed change in the laws of
1hought would have to be interpreted in this way too; this could be no more thnn an apparent change and would be an indication that our knowledge of 1hese laws was incomplete. Now if by the laws of thought we understand the luws of logic, it is easy to see the absurdity of a condition relating, say, to the phosphorus content of our brains or to something else in human beings which is subject to change. In that case it would be quite possible that such a dtunge should have taken place in some people, but not in others, so that for Nomc people there would follow from certain truths the opposite to what would follow for others. This is utterly contrary to the nature of a law of In~tic, since it is contrary to the sense of the word 'true', which excludes any tciCrence to a knowing subject.
If, on the other hand, by the laws of thought we understand psychological luws, then we cannot rule out in advance the possibility that they should l'onlain mention of something that varies with time and place and, nl'wrdingly, that the process of thinking is different nowadays from what it wus 3000 years ago.
I,ogic, in common with every science, has its technical terms, words some uf which are also used outside the sciences, though not in quite the same ? ruse. It doesn't matter in the least if the meaning we fix on is not altogether In line with the everyday use of the word or it doesn't accord with its olymology; what does matter is that the word should be as appropriate a vehicle as possible for use in expressing the laws. Provided there is no loss of rl1uur, the more compendious the formulation of the whole system of laws I? . I he more felicitous is the apparatus of technical terms.
The task of logic being what it is, it follows that we must turn our backs 1111 unything that is not necessary for setting up the laws of inference. In pltrticular we must reject all distinctions in logic that are made from a purely p? ychological standpoint and have no bearing on inference. Similarly, in pure mechanics we don't distinguish substances according to their chemical properties, but speaks only of 'mass' and physical bodies, so that we don't h~tve, say, to establish a special law for each chemical substance in place of the one law of inertia. Therefore let us only distinguish where it serves our purpose. The so-called deepening of logic by psychology is nothing but a raiNiflcation of logic by psychology. In the form in which thinking naturally llovelops the logical and the psychological are bound up together. The task In hund is precisely that of isolating what is logical. This does not mean that
we want to banish any trace of what is psychological from thinking as it nMiurally takes place, which would be impossible; we only want to become ~twure of the logical justification for what we think. So the required 1epuration of the logical from the psychological is only a matter of
? ? 6 Logic
distinguishing in our minds between them. That is why we cannot give too many warnings against the danger of confusing points of view and switching from one question to another, a danger to which we are particularly exposed because we are accustomed to thinking in some language or other and because grammar, which has for speech a significance analogous to that which logic has for thought, is a mixture of the logical and the psychological. Otherwise all languages would necessarily have the same grammar. Can the same thought be expressed in different languages? Without a doubt, so far as the logical kernel is concerned; for otherwise it would not be possible for human beings to share a common intellectual life. But if we think of the kernel with the psychological husk added, a precise translation is impossible. Indeed we may go so far as to doubt whether the outer covering is the same for any two men. From this we can see the value of learning foreign languages for one's logical education; when we see that the same thought can be worded in different ways, our mind separates off the husk from the kernel, though, in any given language, it appears as a natural and integral part of it. This is how the differences between languages can facilitate our grasp of what is logical. But still the difficulties are not wholly removed in this way and our logicians still keep dragging in a number of things which are really of no logical concern, though they belong to the grammar of languages akin to our own, if not to others. For this reason it is useful to be acquainted also with a means of expression of a quite different kind, such as we have, for instance, in the formula-language of algebra. *
But even when we have completely isolated what is logical in some form or phrase from the vernacular or in some combination of words, our task is still not complete. What we obtain will generally turn out to be complex; we have to analyse this, for here as elsewhere we only attain full insight by pressing forwards until we arrive at what is absolutely simple. In this respect, too, logic, because of its attachment to language and grammar, has fallen short in a number of ways. The laws of logic are themselves truths and here again there arises the question how a judgement is justified. If it is not justified in terms of other truths, then logic doesn't need to bother itself with it any further. If, on the other hand, a law of logic can be reduced to other laws by a process of inference, then it is evidently the task of logic to carry out this reduction; for it is only by doing this that we can reach a vantage point from which we can take a conspectus of the laws of logic, and not count as many a law that is one and the same.
To sum up briefly, it is the business of the logician to conduct an unceasing struggle against psychology and those parts of language and
*In this connection mention might also be made of my concept-script. I would not be in a position to write this work on logic without benefit of my earlier endeavours to devise a concept-script.
? Logic 7
l(rammar which fail to give untrammelled expression to what is logical. He does not have to answer the question: how does thinking normally take place in human beings? What course does it naturally follow in the human 111ind? What is natural to one person may well be unnatural to another. To . ~ee this we need look no further than to the great difference between l(rammars. There is no reproach the logician need fear less than the 1eproach that his way of formulating things is unnatural, that the actual 11rocess of thinking follows a different course. If you aim to teach a beginner the rudiments of mathematics in as logically rigorous a form as possible, he will, unless he is quite exceptional, find this very unnatural, and for the very 1enson that such a degree of rigour is employed. As a result, he will understand what he is taught either not at all or only imperfectly. Therefore, oue needs to temper the rigour of one's approach in the early stages, and o11ly as one advances try by degrees to arouse a need for it. Even in utathematics we find that the most rigorous work always belongs to the lntcst stages in the history of the subject. If we were to heed those who ? ? h. iect that logic is unnatural, we would run the risk of becoming embroiled 111 interminable disputes about what is natural, disputes which are quite 1111:apable of being resolved within the province of logic, and which therefore lluvc no place in logic at all. Perhaps definitive answers are simply not to be hud, or cannot be given until we have observed primitive peoples and made u scientific study of languages.
[B. ] Content of possible judgement
Inwardly to recognize something as true is to make a judgement. Thus an instance of a content of possible judgement is the content of the equation 2 1 3 ~ 5. As we have seen, such a content is not the result of an inner pro- cess or the product of a mental act which men perform, but something objective: that is to say, it is something that is exactly the same for all mtional beings, for all who are capable of grasping it, just as the sun, say, is 11ornething objective. But isn't the sun perhaps for some people a beneficent or maleficent deity, for others a shining disk hurled into the heavens from the oust and rolling back down again towards the west, and for yet others an Immense, spherical white-hot body enveloped by a cloud of incandescent I&IINcs'! No. To some it may seem one thing, to others another; it is what it is.
A judgement is often preceded by questions. A mathematician will formulate a theorem to himself before he can prove it. A physicist will 11. a:cpt a law as an hypothesis in order to test it by experience. We grasp the l)unlcnt of a truth before we recognize it as true, but we grasp not only this; we grasp the opposite as well. In asking a question we are poised between opposite sentences. Although it is usually only one side that is expressed when we speak,? the other is still always implied; for the sense of the
? Here, of course, we are referring only to sentence-questions, not to wurd questions.
? 8 Logic
question remains the same if we add 'or not? '. It is this very fact which makes possible such verbal economy. Now whatever can thus be posed in a question, we wish to call a content of possible judgement. Therefore the content of any truth is 'a content of possible judgement', but so too is the opposite content. This opposition or conflict is such that we automatically reject one limb as false when we accept the other as true, and conversely. The rejection of the one and the acceptance of the other are one and the same.
? Boole's logical Calculus and the Concept-script1 [1880/81]
In his writings, Leibniz threw out such a profusion of seeds of ideas that in IIus respect he is virtually in a class of his own. A number of these seeds wrrc developed and brought to fruition within his own lifetime and with his 11tllaboration, yet more were forgotten, then later rediscovered and drvcloped further. This justifies the expectation that a great deal in his work lhul is now to all appearance dead and buried will one day enjoy a rr,urrcction. As part of this, I count an idea which Leibniz clung to lluuughout his life with the utmost tenacity, the idea of a lingua l'haracterica, an idea which in his mind had the closest possible links with lhnl of a calculus ratiocinatur. That it made it possible to perform a type of ru111putation, it was precisely this fact that Leibniz saw as a principal ndvanlage of a script which compounded a concept out of its constituents rnl her than a word out of its sounds, and of all hopes he cherished in this muller, we can even today share this one with complete confidence. I will IJlrulc just the following from the relevant passages:
'Si daretur vel lingua quaedam exacta, vel genus scripturae vere philosophiae, . . . omnia quae ex datis ratione assequi, inveniri possent l. fUodam genere calculi, perinde ac resolvuntur problemata arithmetica aut jcomctrica. '*
? I>c Scientia universali seu calculo philosophico.
1 In 188 I, this article was submitted by Frege in turn to the Zeitschrift fiir Matlrematik und Physik, the Mathematischen Annalen and the Zeitschrift fiir l'lr/lu. wphie und philosophisehe Kritik, but was in every case rejected by the editors. lllluully remained unpublished.
l'rom the report of H. Scholz and F. Bachmann: Der wissenschaftliche Nachlass r? mt {,'o/1/ob Frege (Paris 1936) we learn that the lost original was 'a manuscript rrrJlnrcd for publication of 103 closely written sides of quarto'. Scholz and lt11chmann mention besides that Frege also submitted the manuscript to R. Avenarius for the Vierteljahrsschrift fii. r wissenschaftliche Philosophie. However it 11uuld be that what Frege submitted to Avenarius was the essay published in this v11lumc on pp. 47 IT. 'Boole's logical Formula-language and my Concept-Script', llnce Avenarius in his letter to Frege of 20/4/1882 cites the title of the manuscript rtlurncd by him as 'Boole's logical Formula-Language'.
The article can scarcely have been composed before 1880, the year in which the rtview by Schroder mentioned on p. 11 appeared. A great number of the reflections
? ? ? 10 Boole's logical Calculus and the Concept-script
Among the various sorties Leibniz made upon his goal, the beginnings of a symbolic logic come closest to what seems to be indicated by the phrase 'calculus ratiocinatur'. They are to be found in the essays:
Non inelegans specimen demonstrandi in abstractis and Addenda ad specimen calculi universalis
In these Leibniz stuck very close to language. Just as the words we use for the attributes of a thing follow one another, so he simply juxtaposes the letters corresponding to properties in order to express the formation of a concept. If, for instance, A means right-angled, B isosceles, C triangle, then Leibniz represents right-angled isosceles triangle by ABC. He uses a sign for identity, oo, and the sign + with the definition:
'A +Boo L significat A inesse ipsi L'.
This seems to coincide with the meaning recent logicians have given this sign, according to which A + B represents the class of individuals which belong to A or to B or to both. Since I am passing over less important details, the only other fact I will mention is that Leibniz allows the words 'non' and 'ens' to occur in his formulae. In this project he surely has the lingua characterica in mind, even though he made no express connection with the attempts he made to represent a content.
This way of setting up a formal logic seems to suggest itself naturally. At any rate recent German and English logicians have arrived at the same conception quite independently of Leibniz, though, as far as I know, in doing so they do not have a general characteristic in mind. However much Boolean logic* may stand out as a systematic working out of the fragmen- tary hints in Leibniz, it only goes beyond him in one point of fundamental importance-in the way it reduces hypothetical and disjunctive judgements to categorical. ? ? The Leibnizian 'ens' is left out.
In a short monograph,? ? ?
