Thus, be it understood, to demonstrate a theorem, it is neither necessary nor even advantageous to know what it means.

Experiment is the sole source of truth. It alone can teach us something new; it alone can give us certainty.

Hypotheses are what we lack the least.

Pure logic could never lead us to anything but tautologies; it can create nothing new; not from it alone can any science issue.

Einstein does not remain attached to the classical principles, and when presented with a problem in physics he quickly envisages all of its possibilities. This leads immediately in his mind to the prediction of new phenomena which may one day be verified by experiment.

Experiment is the sole source of truth.

It is by logic that we prove, but by intuition that we discover. To know how to criticize is good, to know how to create is better.