The ego is as little absolutely permanent as are bodies.

Man is pre-eminently endowed with the power of voluntarily and consciously determining his own point of view.

To us investigators, the concept 'soul' is irrelevant and a matter for laughter. But matter is an abstraction of exactly the same kind, just as good and just as bad as it is. We know as much about the soul as we do of matter.

If our dreams were more regular, more connected, more stable, they would also have more practical importance for us.

The ego is as little absolutely permanent as are bodies.

Thought experiment is in any case a necessary precondition for physical experiment. Every experimenter and inventor must have the planned arrangement in his head before translating it into fact.

Science always has its origin in the adaptation of thought to some definite field of experience.