No More Learning

He will
have added nothing to the gross produce of the land: he has consumed a
portion of this gross produce, and has left a bit of lace in return;
and though he may sell this bit of lace for three times the quantity of
provisions that he consumed whilst he was making it, and thus be a very
productive           with regard to himself, yet he cannot be considered
as having added by his labour to any essential part of the riches of
the state.