Success in solving the problem depends on choosing the right aspect, on attacking the fortress from its accessible side.

I am intentionally avoiding the standard term which, by the way, did not exist in Euler's time. One of the ugliest outgrowths of the "new math" was the premature introduction of technical terms.

The principle is so perfectly general that no particular application of it is possible.

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

An idea which can be used only once is a trick. If one can use it more than once it becomes a method.

The first rule of style is to have something to say. The second rule of style is to control yourself when, by chance, you have two things to say; say first one, then the other, not both at the same time.

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.