What capital I give for the spade merely replaces what the manufacturer had already invested in the expectation that the spade would be needed. - William Stanley Jevons

Previous to the time of Pascal, who would have thought of measuring doubt and belief? Who could have conceived that the investigation of petty games of chance would have led to the most sublime branch of mathematical science - the theory of probabilities?

In any case I hold that there must arise a science of the development of economic forms and relations.

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.