117 Quotes by Charles Sanders Peirce

Abduction is the process of forming an explanatory hypothesis. It is the only logical operation which introduces any new idea; for induction does nothing but determine a value and deduction merely evolves the necessary consequences of a pure hypothesis.

Are you sure twice two are four? Not at all. A certain percentage of the human race are insane and subject to illusions. It may be you are one of them, and that your idea that twice two is four is a lunatic notion, and your seeming recollection that other people think so, the baseless fabric of a vision.

A pair of statements may be taken conjunctively or disjunctively; for example, “It lightens and it thunders ,” is conjunctive, “It lightens or it thunders” is disjunctive. Each such individual act of connecting a pair of statements is a new monad for the mathematician .

The consciousness of a general idea has a certain “unity of the ego” in it, which is identical when it passes from one mind to another. It is, therefore, quite analogous to a person, and indeed, a person is only a particular kind of general idea.

We think only in signs.

All human affairs rest upon probabilities, and the same thing is true everywhere. If man were immortal he could be perfectly sure of seeing the day when everything in which he had trusted would betray his trust, and, in short, of coming eventually to hopeless misery. He would break down, at last, as every great fortune, as every dynasty, as every civilization does. In place of this we have death.

Unless man have a natural bent in accordance with nature’s, he has no chance of understanding nature at all.

Few persons care to study logic, because everybody conceives himself to be proficient enough in the art of reasoning already. But I observe that this satisfaction is limited to one’s own ratiocination, and does not extend to that of other men.

Theoretically, I grant you, there is no possibility of error in necessary reasoning. But to speak thus “theoretically,” is to uselanguage in a Pickwickian sense. In practice, and in fact, mathematics is not exempt from that liability to error that affects everything that man does.