Look around when you have got your first mushroom or made your first discovery: they grow in clusters.

In order to solve this differential equation you look at it until a solution occurs to you.

One of the first and foremost duties of the teacher is not to give his students the impression that mathematical problems have little connection with each other, and no connection at all with anything else. We have a natural opportunity to investigate the connections of a problem when looking back at its solution.

Mathematics consists in proving the most obvious thing in the least obvious way.

The first rule of discovery is to have brains and good luck. The second rule of discovery is to sit tight and wait till you get a bright idea.

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

I am too good for philosophy and not good enough for physics. Mathematics is in between.