A correct theory is the first step towards improvement, by showing what we need and what we might accomplish. - William Stanley Jevons

All acts of reasoning seem to me to be different cases of one uniform process which may perhaps be best described as the substitution of similars. ..The chief difficulty consists in showing that all the forms of the old logic, as well as the fundamental rules of mathematical reasoning, may be explained upon the same principle; and it is to this difficult task I have devoted the most attention.

Capital simply allows us to expend labour in advance.

One of the first and most difficult steps in a science is to conceive clearly the nature of the magnitudes about which we are arguing.