Mathematics is made of 50 percent formulas, 50 percent proofs, and 50 percent imagination.

"A mathematician is a device for turning coffee into theorems" (P. Erdos)

Addendum: American coffee is good for lemmas.

An engineer thinks that his equations are an approximation to reality. A physicist thinks reality is an approximation to his equations. A mathematician doesn't care.

Old mathematicians never die; they just lose some of their functions.

Mathematicians are like Frenchmen: whatever you say to them, they translate it into their own language, and forthwith it means something entirely different. -- Goethe

Mathematics is the art of giving the same name to different things. -- J. H. Poincare

What is a rigorous definition of rigor?

There is no logical foundation of mathematics, and Gödel has proved it!

I do not think -- therefore I am not.