What we see changes what we know. What we know changes what we see.

Logical positivists have never taken psychology into account in their epistemology, but they affirm that logical beings and mathematical beings are nothing but linguistic structures.

In other words, knowledge of the external world begins with an immediate utilisation of things, whereas knowledge of self is stopped by this purely practical and utilitarian contact.

Scientific thought, then, is not momentary; it is not a static instance; it is a process.

To express the same idea in still another way, I think that human knowledge is essentially active.

Equilibrium is the profoundest tendency of all human activity.

Chance... in the accommodation peculiar to sensorimotor intelligence, plays the same role as in scientific discovery. It is only useful to the genius and its revelations remain meaningless to the unskilled.