The series of integers is obviously an invention of the human mind, a self-created tool which simplifies the ordering of certain sensory experiences.

Though our conduct seems so very different from that of the higher animals, the primary instincts are much alike in them and in us.

Applying the axioms of physical science to human life has something reprehensible to it.

Make everything as simple as possible, but not simpler. A man should look for what is, and not for what he thinks should be. We cannot solve our problems with the same thinking we used when we created them. A question that sometimes drives me hazy: am I or are the others crazy? Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. All religions, arts and sciences are branches of the same tree. It's not that I'm so smart, it's just that I stay with problems longer.

A new idea comes suddenly and in a rather intuitive way, but intuition is nothing but the outcome of earlier intellectual experience.

Nobody knows how the stand of our knowledge about the atom would be without him. Personally, [Niels] Bohr is one of the amiable colleagues I have met. He utters his opinions like one perpetually groping and never like one who believes himself to be in possession of the truth.

At present every coachman and every waiter argues about whether or not the relativity theory is correct.