Intelligence is what you use when you don't know what to do.

During the earliest stages the child perceives things like a solipsist who is unaware of himself as subject and is familiar only with his own actions.

I have always detested any departure from reality, an attitude which I relate to my mother's poor mental health.

Scientific knowledge is in perpetual evolution; it finds itself changed from one day to the next.

Equilibrium is the profoundest tendency of all human activity.

To understand is to invent.

The current state of knowledge is a moment in history, changing just as rapidly as the state of knowledge in the past has ever changed and, in many instances, more rapidly.