So you
distinguish
two kinds of ideas?
Gottlob-Frege-Posthumous-Writings
(2) Disregarding content, within the domain of pure logic it also, thanks to the notation for generality, commands a somewhat wider domain than Boole's formula-language.
(3) It avoids the division in Boolean logic into two parts (primary and secondary propositions) by construing judgements as prior to concept formation.
(4) It is in a position to represent the formations of the concepts actually needed in science, in contrast to the relatively sterile multiplicative and additive combinations we find in Boole.
(5) It needs fewer primitive signs for logical relations and hence fewer primitive laws.
(6) It can be used to solve the sort of problems Boole tackles, and even do so with fewer preliminary rules for computation. This is the point to which I attach least importance, since such problems will seldom, if ever, occur in science.
? ? Boole's logical Formula-language and my Concept-script1 [1882]
Since this journaJ2 has already devoted some attention to the Boolean presentation of logical laws by means of equations, I hope that a comparison of it with another way of designating logical relations, proposed by me,* will not be unwelcome. First, however, I would like to stress that the aim of my concept-script is different from that of Boolean logic. I wanted to supplement the formula-language of mathematics with signs for logical relations so as to create a concept-script which would make it possible to Jispense with words in the course of a proof, and thus ensure the highest degree of rigour whilst at the same time making the proofs as brief as possible. For this purpose the signs I introduced had to be such as were suitable for combining of themselves with those ordinarily employed in mathematics. The Boolean signs (in part stemming from Leibniz) are completely unsuited to this, which is scarcely to be wondered at when you consider their purpose; they are merely meant to present the logical form with no regard whatever for the content. I think it is necessary to preface my remarks in this way to guard against the false impression that one could validly compare the two scripts in every respect.
It is only the second part of Boolean logic-the part dealing with secondary propositions-that I wish to investigate here, leaving open the possibility of my taking the comparison further on another occasion. By secondary propositions Boole understands hypothetical, disjunctive, and in general such judgements as state a relation between contents of possible judgement, as opposed to the primary propositions, in which concepts are set in relation to one another. I make a distinction between judgement and content of possible judgement, reserving the first word for cases where such n content is put forward as true.
If, therefore, it is a question of setting two contents of possible judgement
* Begriffsschrift, Halle a. S. 1879.
1 In all probability this essay contains the content of a manuscript returned to hegc by R. Avenarius with the letter of 20/4/1882. Avenarius there cites the title us 'Boole's logical formula-language' and rejects the manuscript for the Vlmeljahrsschrijlfiir wissenschaftliche Philosophie (ed. ).
2 Vierteljahrsschrij/ fiir wissenschqftliche Philosophle.
? 48 Boole's logical Formula-language and my Concept-script
A and B in relation, we have to hold before our minds the following
cases:
the equals sign
the addition sign
the multiplication sign
and subtraction sign
A=B,
A +B,
A ? B,
A-B.
A andB,
A andnotB, notA andB,
not A and not B.
These cases can for their part be either affirmed or denied. Now Boole has
We may here disregard logical division as less important.
The equals sign for Boole affirms the denial of the two middle cases, so
that the cases left open are 'A and B' and 'not A and not B'. In 'A = 1' and 'B = 0' the assertoric force of the identity sign stands out unalloyed. The first equation puts A forward as true, the second B as false. For Boole 'A + B' means the denial of the first and the last cases, leaving open the two middle ones. You can translate it as 'A orB', where 'or' is to be understood in the exclusive sense. Leibniz and some of Boole's followers, such as S. Jevons and E. Schroder, have kept the meaning of the inclusive 'or' for the + sign. In that case only the last of the four cases is denied by 'A + B'. 'A ? B' means the first case, 'A and B'. The denial of a content of possible judgementisexpressedbyBoolebymeansof'1- A',andbyothersinother ways. To this is added the above-mentioned 'A = 0' for the case where the denial is expressed as a judgement. Some people have a further sign for inequality, which also includes a denial. What strikes one in all this is the superfluity of signs. This, in its turn, entails a superfluity of primitive rules for computation. The reason for this lies doubtless in the desire to force on logic signs borrowed from an alien discipline, instead of taking one's departure from logic itself and its own requirements.
I have followed another path, by giving to each primitive sign as simple a meaning as possible. If, given two designations, one says all that is meant by the other, but not conversely, I call the meaning of the second simpler than that of the first, because it has less content. If we now apply this yardstick we see that the simplest relation of two contents of possible judgement results from denying one of the four cases
? Boole's logical Formula-language and my Concept-script 49
A andB,
A andnotB, notA andB,
not A and not B,
for the denial of two of these cases says more than that of one on its own, and the denial of three even more: it is tantamount to the affirmation of the fourth case. None of the Boolean signs meets the requirement that the meaning is the simplest possible. It is only met by the + sign in the sense adopted E. Schroder,? of the inclusive 'or'. The advantage of the latter makes itself immediately felt in the greater adaptability of the formulae when compared with Boole's. I don't understand how W. Schlotel** can find anything slovenly in this. This objection would only be justified if the meaning, once adopted, were not adhered to in what followed. Whether a special sign is adopted for the inclusive 'or' or not is merely a question of convenience. Now the exclusive 'A orB' contains two things:
1. That one of the two obtains 2. That they don't both obtain.
Since these two don't always go together, since rather, by the laws of probability, their combination is rarer than either on its own, it is more convenient for the individual cases which occur more frequently to have signs of their own that it is for their combination, which is relatively uncommon. And even when A and B do stand in the exclusive 'or' relation, almost invariably only one of the two will come into consideration in a given inference: either that A and B are not both false, or that they are not both true. For the rarer exclusive 'A or B', Boole has the simple designation
'A + B', for the commoner inclusive 'A or B', the complex expression 'A +- B(l -A)'. In the case of Schroder the converse is true: he renders the former by 'AB1 + A1B', the latter by 'A + B'. The suffix 1 here means a
denial, so that A
The Boolean 'A = B' contains three things:
1. that A doesn't obtain without B, 2. that B doesn't obtain without A; 3. the judgement that this is so.
I Iere too the combination is given the honour of a simple designation, while the constituent elements have to be content with complex expressions.
As the affirmation of the first case, Boole's logical product 'A? B' means the denial of the last three of our cases, and so is very rich in content. llowever this designation is more convenient than the others, since we ohtain a simple content by mere denial of such a product.
If one wishes to avoid the defect in the Boolean signs we have just
? Der Operationskreis des Logikkalkuls. Leipzig 1877. ? ? Vierteljahrsschriftfiir wissenschqftl. Phi/os. I, p. 456.
1
means the denial of A.
? 50 BooZe's logical Formula-language and my Concept-script
emphasized, one must introduce a special designation for the denial of one of the four cases set out above. It is enough for this purpose to select a single one of tliose cases for by using a negation sign one can obtain from each of the four cases any other. If, for instance, we put r for the denial of A those four cases then run:
not rand B,
not rand not B,
randB, rand notB;
that is the first case has assumed the form of the third, the second that of the fourth, and conversely the third that of the first, the fourth that of the second. If now it is possible to manage with one single sign which denies one of the four cases, we ought to do so, for the fewer primitive signs one introduces, the fewer primitive laws one needs, and the easier it will be to master the formulae.
Now, I have chosen the third case 'not A and B' as the one whose denial receives a special sign:
To form the denials of the remaining cases, I make use of the negation- stroke, a small vertical stroke attached beneath one of the horizontal strokes. So
means the denial of 'not not A and B', i. e. of 'A and B',
the denial of the case 'A and not B',
the denial of the case 'not A and not B'.
If the cases are to be affirmed, instead of denied, this is done by means of
a negation-stroke attached to the left hand end of the uppermost horizontal stroke. Accordingly
means 'not A and B',
? r
BooZe's logical Formula-language and my Concept-script 51
'A and B',
? A and not B', and finally
'not A and not B'. It is easy to see that you can translate
by 'A orB' in the inclusive sense, and
by 'neither A nor B'.
Nothing is yet asserted, no judgement is made, by all these designations;
only a new content of possible judgement is formed from given ones. Now in order to put a content forward as true, I make use of a small vertical stroke, the judgement stroke, as in
whereby the truth of the equation is asserted, whereas in - 3 2 = 9 no judgement has been made. Hence since the judgement stroke is lacking, we can even write down - 3 2 = 4 without saying anything untrue. If we include the negation-stroke, we can add the judgement stroke too without falling into error
means: 32 is not equal to 4 By
l2=4 t1+3=5
the fact that the case that 12 is not equal to 4 and that 1 + 3 = 5 does not obtain is asserted; and this rightly, since 1 + 3 simply is not equal to 5. Like- wise it is correct to put the judgement stroke in
22 = 4 t2+3=5
because the case that 22 is not equal to 4 and 2 + 3 = 5, does not obtain; for, of course 22 = 4. Similarly
? 52 Boole's logical Formula-language and my Concept-script
is right for two reasons: because (-2)2 = 4, and because -2 + 3 does not
equal 5. Whatever number you may put in the place of the 1 in
12=4 T1+3=s
the content is always correct. To express this general assertion, I use a roman letter:
Youcanalsorenderthis:ifx+3= 5,thenx2= 4. Andsowehaveherea hypothetical judgement. And the outstanding importance of this judgement has persuaded me to give the sign
precisely the meaning of the denial of the case 'not A and B'. Of course this alone doesn't yet give us a genuine hypothetical judgement: that arises only when A and B have in common an indefinite component which makes the situation described general.
I believe I have now adequately shown, that, as is proper, I divide the different tasks with which Boole burdens the one sign among several signs, without thereby increasing the total number of signs. The signs which I have also introduced elsewhere may be ignored in this context, since I am restricting myself to what corresponds to Boole's secondary propositions. As against his addition, subtraction, multiplication and equals signs, and his 0 and 1, we have:
1. The horizontal 'content-stroke',
2. The negation-stroke,
3. The vertical stroke that combines two content-strokes, 'the
conditional-stroke',
4. Theverticaljudgement-stroke.
Here, I haven't counted Boole's division sign and other numbers besides 0 and 1, since these are easier to dispense with.
? I. Piinjer:
2. Frege: J. P. 4. F.
5. P.
6. F.
7. P. H. F.
Y. P. 10. P.
11. F. 12. P.
1
[Dialogue with Piinjer on Existence] 1 [Before 1884]
[I. The Dialogue]
'Something does not have the characteristic of flying, but does fall under the concept "bird'": does this have the same meaning as 'Among what is, is something that does not have the characteristic of flying, but does fall under the concept "bird"'? What does is mean?
It means can be experienced (by us).
Is it not pleonastic to say of something that it can be experienced?
No, since by manipulating at will the ideas derived from experience, we are able to form ideas to which nothing that can be experienced corresponds.
Is it A or the idea ofA that is the real, as opposed to the grammatical, subject in the sentence 'A is something that can be experienced'.
A.
'The statement "A cannot be experienced" is the negation of the statement "A can be experienced"'. Is that correct?
Yes, if by 'A cannot be experienced' is understood: the sentence 'A can be experienced' is false.
The statement 'A cannot be experienced' is not possible. Therefore the question is nonsensical. Neither does it make sense to deny that a thing can be experienced.
In that case it seems to me pleonastic to say of something that it can be experienced.
'There are men' means 'To the concept man there corresponds something that can be experienced'. Or 'One of the things that
Frege's partner in the dialogue is the protestant theologian Bernard Piinjer ( IHS0-1885), who held a chair at Jena from 1880. Both the parenthetical remark at K4 and the style of Piinjer's contributions leave no doubt that what we have in I is the record of a dialogue which actually took place. According to comments on the copies that have been preserved, the manuscript to 11 was found in an envelope together with the transcript of the dialogue.
Frcge's own more rigorous treatment of the theme in the Grundlagen (? 53) provides a clue for dating the two manuscripts. In any case the date of Piinjer's death sets an upper limit to the time of composition (ed. ).
? 54
[Dialogue with Piinjer on Existence]
13. F. 14. P.
15. F. 16. P. 17. F.
18. P.
19. F. 20. P.
21. F.
22. P.
23. F.
can be experienced falls under the concept man'. 'There are no centaurs' means 'To the idea or concept centaur there corresponds nothing that can be experienced'.
Here the negation goes with the 'corresponds'.
Yes. Or none of the things which can be experienced fall under the concept centaur.
To say of a thing that it can be experienced is not to characterize it in any way.
No. That is the difference between this statement and the others.
It still seems to me therefore as if it is pleonastic to say of something that it can be experienced, because by saying this we learn nothing new about the subject. You just explained 'There are' and why such judgements are not pleonastic, but you did not explain why the judgement 'This can be experienced' is not pleonastic.
'This can be experienced' means 'The idea of the "this" is not an hallucination, it is not something which originates from myself alone; but the idea has been formed as a result of the ego's being affected by the this'.
So you distinguish two kinds of ideas?
Yes; there are two kinds of idea: those that originate from the ego alone, and those that are formed through something affecting the ego. In order to distinguish these I say: the objects of ideas of the latter kind can be experienced; to ideas of the former kind there do not correspond any objects that can be experienced.
It seems to me then as if the real subject on your way of thinking is the idea. Do you not admit that in every substantive statement the real subject is assigned to a class and is thereby distinguished from other things that do not belong to that class?
I admit that; but a statement of existence is not a substantive one. I do not admit it if by 'substantive' is understood 'not self- evident', 'not containing a purely logical law'.
When you say 'There are men' and 'There are no centaurs' you are also making a classification. But you are not classifying things, which in one case are not there at all, and in the other case are not being assigned to one of two classes, but you are classifying the concepts 'man' and 'centaur' by assigning one to the class of concepts under which something falls, and excluding the other from this class. This is why I hold that in these sentences the concepts are the real subjects. If you say 'This can be experienced', where this has the sense 'This idea of mine is not something originating from myself alone', then you
? ? 24. P.
25. F.
26. P.
are classifying the idea. You are assigning it to one of the two kinds that you distinguished earlier. This is why I maintain that it is here the idea that is the real subject. Another way of putting the same thing is to say: The idea has the property that something corresponds to it.
A t this point the question arises o f what negation is. Negation is possible only when something has already been posited. Hence if we say 'Centaurs do not exist', this is possible only because we first think of them as being outside ourselves. We have a twofold ground for denying existence: I. a logical contradiction, 2. outside the concept or idea in experience. 1 So properly speaking the real subject is neither the concept nor the idea.
In saying this you are only citing the ground on which we base a judgement about existence. One can also derive a judgement like 'There are square roots of 4' from the concept of the square root of 4.
'There are square roots of 4' does not mean 'there is something that can be experienced which falls under the concept square root of 4', if we understand by what can be experienced something self-subsistent, something existing in its own right. Numbers exist only in something. Hence this judgement is essentially different from the judgement 'there are men'. I shall never say '4 exists'. And equally I shall not say 'a square root of 4 exists'. Here the 'there is' is used in a different sense. It means: it is a property of 4 that it can result from multiplying a number by itself, that one can find a number which yields 4 when multiplied by itself. We can only make the judgement after we have formed the proposition 22 = 4 (or (-2)2 = 4). This is what it has in common with the other existential judgements such as 'there are men'.
It was earlier objected to me with the example 'there are square roots of 4' that this is an existential judgement. Now you seem not to count it as such, because you do not want to say 'A square root of 4 exists'.
'There are square roots of 4' is an existential judgement.
(on 18) The proposition 'The idea of the this has been formed as a result of the ego's being affected by the this' is self-evident, if it is possible without absurdity to formulate its content at all; for we cannot use the expression 'The idea of this' before we have made the judgement 'Something corresponds to this idea of mine' or 'This idea of mine has been formed as a result of
27. F.
28. P. 29. F.
[Dialogue with Piinjer on Existence] 55
1 These are the words as they occur in the manuscript (ed. ).
? 56
[Dialogue with Piinjer on Existence]
30. P.
31. F.
32. P. 33. F.
something affecting the ego'. Only then can we assign the name 'this' to what has done the affecting, to what corresponds to my idea.
'The idea of the this has been formed as a result of the ego's being affected by the this' is only another way of saying 'To this idea of mine there corresponds something that can be experienced'.
I understand your remark (20) in the following way: If you want to say that B is an idea that does not originate from the ego alone, but is formed through something affecting the ego, then you use the words 'The object of B can be experienced'. The two sentences are synonymous. Is that right?
Instead of 'B is an idea that etc. ' I should say 'The idea B is etc. ', assuming straight off that B is an idea.
I grant that it is not self-evident and pleonastic to say 'The idea B does not originate from the ego alone, but is formed through something affecting the ego'; for not every idea is formed through something affecting the ego; at least the point is a debatable one. The negation of this sentence would be 'The idea B is not formed through something affecting the ego' if we assume that B is an idea. In that case the negation has a perfectly good sense and hence it is not pleonastic and self- evident to utter the sentence 'The idea B is formed through something affecting the ego' or the sentence 'The object of B can be experienced', which you maintain to have the same meaning. But if these sentences have the same meaning, then in the judgement 'The negation of the sentence "The idea B is formed through something affecting the ego" has a good sense' we may replace 'The idea B is formed through something affecting the ego' by 'The object of B can be experienced'. We then obtain the judgement: The negation of the sentence 'The object of B can be experienced' has a good sense. This contradicts your earlier position.
There is no contradiction in calling the negation of the statement 'The object of the idea B can be experienced' legitimate, but the negation of the statement 'The object B can be experienced' illegitimate.
If I understand you rightly, the contradiction is resolved as follows: In the expression 'The object of the idea' the word 'object' is used in a different sense from in 'The object A can be experienced'.
No. The word 'object' has the same meaning, but 'object of an idea' means something different from 'object'.
Does adding 'of an idea' merely serve to restrict the sense? 'Object' by itself means object that is not merely object of an
34. P.
35. F.
36. P. 37. F.
38. P.
? ? . W. P. 40. F.
41. P.
42. F. 43. P. -14. F.
45. P. 4h. F.
47. P. 4H. F.
41). P. 50. F. 51. P. 52. F.
53. P.
54. F. 55. P. 5o. F.
57. P. 5H. F.
[Dialogue with Piinjer on Existence] 57 idea, but of experience. The contrast to draw should really be
that between object of an idea and object of experience.
(referring to 26 & 27) Number cannot be experienced in the same sense as Paul.
So you distinguish two senses of'can be experienced'?
No. Number can be experienced in the same general sense. The concept of that which can be experienced is in both cases the same; it is the same whether I say number, thing or colour can be experienced.
You do not always understand by 'can be experienced' something that can be experienced on its own?
What cannot be experienced on its own can still be experienced, as e. g. a colour, which can only be experienced in something. You said (26) that you would not say '4 exists'. Are you here using 'exist' in the same sense as 'capable of being ex- perienced'?
Yes, I take it back that I would not say '4 exists', 'a square root of 4 exists'.
The difference between the judgements 'There are men' and 'There are square roots of 4' does not lie in the 'there are' but in the difference between the concepts 'man' and 'square root of 4'. We understand by a man something that exists in its own right, but we do not understand this by a square root of 4.
I agree with that.
Is the sentence 'A can be experienced' right, if A is taken to be an idea?
Yes. An idea can be experienced.
Is there an idea of an idea?
There are ideas of ideas.
You once referred to an idea as a fluctuating image, a series of inner perceptions. What are the inner perceptions out of which the idea of the idea A is formed?
They are the particular mental acts performed in having the idea A.
Do 'act of forming an idea' and 'idea' mean the same?
Yes.
So we are wrong to distinguish the act of forming an idea from an idea.
Yes.
From your remarks (18) and (20) it follows that 'This can be experienced' has the same meaning as 'To this idea of mine there corresponds something that can be experienced'. Here 'can be experienced' is defined in terms of itself.
? ? ? 58
[Dialogue with Piinjer on Existence]
59. P.
60. F. 61. P.
62. F. 63. P.
64. F. 65. P. 66. F.
67. F. 68. P.
69. F. 70. P.
71. F. 72. P. 73. F.
74. P. 75. F.
