The electron is a theory we use; it is so useful in understanding the way nature works that we can almost call it real.
Richard P. FeynmanEverybody who reasons carefully about anything is making a contribution ... and if you abstract it away and send it to the Department of Mathematics they put it in books.
Richard P. FeynmanWords can be meaningless. If they are used in such a way that no sharp conclusions can be drawn.
Richard P. Feynman