The cookbook gives a detailed description of ingredients and procedures but no proofs for its prescriptions or reasons for its recipes; the proof of the pudding is in the eating. ... Mathematics cannot be tested in exactly the same manner as a pudding; if all sorts of reasoning are debarred, a course of calculus may easily become an incoherent inventory of indigestible information.

George Pólya— p. 219 (How to Solve It (1945))

For mathematics education and the world of problem solving it marked a line of demarcation between two eras, problem solving before and after Polya.

George Pólya— A. H. Schoenfeld, in "Polya, Problem Solving, and Education" in

Analogy pervades all our thinking, our everyday speech and our trivial conclusions as well as artistic ways of expression and the highest scientific achievements.

George Pólya— p. 37 (How to Solve It (1945))

The best of ideas is hurt by uncritical acceptance and thrives on critical examination.

George Pólya— p. 100 (How to Solve It (1945))

We need heuristic reasoning when we construct a strict proof as we need scaffolding when we erect a building.

George Pólya— p. 113 (How to Solve It (1945))

Pedantry and mastery are opposite attitudes toward rules. To apply a rule to the letter, rigidly, unquestioningly, in cases where it fits and in cases where it does not fit, is pedantry. ... To apply a rule with natural ease, with judgment, noticing the cases where it fits, and without ever letting the words of the rule obscure the purpose of the action or the opportunities of the situation, is mastery.

George Pólya— p. 148 (How to Solve It (1945))

Euclid 's manner of exposition, progressing relentlessly from the data to the unknown and from the hypothesis to the conclusion, is perfect for checking the argument in detail but far from being perfect for making understandable the main line of the argument.

George Pólya— p. 70 (How to Solve It (1945))