Karl Popper Quotes

Logic is an old subject, and since 1879 it has been a great one.

Contrariwise, if it was so, it might be; and if it were so, it would be; but as it isn't, it ain't. That's logic.

Facts are not truths; they are not conclusions; they are not even premises, but in the nature and parts of premises.

There is a tradition of opposition between adherents of induction and of deduction. In my view it would be just as sensible for the two ends of a worm to quarrel.

The example of a syllogism that he had studied in Kiesewetter's logic: Caius is a man, men are mortal, therefore Caius is mortal, had throughout his whole life seemed to him right only in relation to Caius, but not to him at all.

Logic is the science of the laws of thought, as thought,--that is of the necessary conditions to which thought considered in itself is a subject.

Aristotelian logic is massive and marmoreal, but every monument accumulates graffiti.

Our reasonings are grounded upon two great principles, that of contradiction, in virtue of which we judge false that which involves a contradiction, and true that which is opposed or contradictory to the false.

Induction for deduction, with a view to construction.

Now this principle of induction cannot be a purely logical truth like a tautology or an analytic statement. . . .

Geometry is beautifully logical, and it teaches you how to think and prove that things are so, step by step by step. Proofs are excellent lessons in reasoning. Without logic and reasoning, you are dependent on jumping to conclusions or - worse - having empty opinions.

Philosophy unravels the knots in our thinking; hence its results must be simple, but its activity is as complicated as the knots that it unravels.

As does every young man studying philosophy, I naturally asked myself questions about the truth of all this, and about the meaning of freedom, predestination, and liberty of choice and so on. But to have asked questions of yourself about it, I think is not too important. Let's say - I remain - I remained a believer.

Anything that thinks logically can be fooled by something else that thinks at least as logically as it does.

Mathematics is a language plus reasoning. It's like a language plus logic. Mathematics is a tool for reasoning.

Logic is the subject that has helped me most in picking stocks, if only because it taught me to identify the peculiar illogic of Wall Street. Actually Wall Street thinks just as the Greeks did. The early Greeks used to sit around for days and debate how many teeth a horse has. They thought they could figure it out just by sitting there, instead of checking the horse. A lot of investors sit around and debate whether a stock is going up, as if the financial muse will give them the answer, instead of checking the company.

The neutral view of free will is impossible. It involves choice without desire.

I can put two and two together, you know. Do not think you are dealing with a man who has lost his grapes.

Philosophy is an unusually ingenious attempt to think fallaciously.

Convictions can best be supported with experience and clear thinking.

If you will take my advice you will think little of Socrates, and a great deal more of truth.

Stupidity is no excuse of not thinking.

Faith is a function of the heart. It must be enforced by reason. The two are not antagonistic as some think. The more intense one's faith is, the more it whets one's reason. When faith becomes blind it dies.

Few of us ever test our powers of deduction, except when filling out an income tax form

Philosophy is a slow process of logic and logical discourse: A bringing B bringing C and so forth. In mysticism you can jump from A to Z. But the ultimate objective is the same. It's knowledge. It's truth.