It is far better to foresee even without certainty than not to foresee at all.

Science is facts; just as houses are made of stones, so is science made of facts; but a pile of stones is not a house and a collection of facts is not necessarily science.

The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.

Thought is only a flash between two long nights, but this flash is everything.

To doubt everything or to believe everything are two equally convenient solutions; both dispense with the necessity of reflection.

Science is built up of facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house.

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

Invention consists in avoiding the constructing of useless contraptions and in constructing the useful combinations which are in infinite minority. To invent is to discern, to choose.

Ideas rose in clouds; I felt them collide until pairs interlocked, so to speak, making a stable combination.