“What we see changes what we know. What we know changes what we see.”

Knowledge, then, is a system of transformations that become progressively adequate.

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

This means that no single logic is strong enough to support the total construction of human knowledge.

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

It is with children that we have the best chance of studying the development of logical knowledge, mathematical knowledge, physical knowledge, and so forth.