In fact the total amount that a physicist knows is very little. He has only to remember the rules to get him from one place to another and he is all right.

When a scientist doesn't know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is in some doubt.

That is the logical tight-rope on which we have to walk if we wish to interpret nature.

The real problem in speech is not precise language. The problem is clear language.

In physics the truth is rarely perfectly clear, and that is certainly universally the case in human affairs. Hence, what is not surrounded by uncertainty cannot be the truth.

First you guess. Don't laugh, this is the most important step. Then you compute the consequences. Compare the consequences to experience. If it disagrees with experience, the guess is wrong. In that simple statement is the key to science. It doesn't matter how beautiful your guess is or how smart you are or what your name is. If it disagrees with experience, it's wrong. That's all there is to it.

All the time you're saying to yourself, 'I could do that, but I won't,'--which is just another way of saying that you can't.