Play is the work of childhood.

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

Every time we teach a child something, we keep him from inventing it himself. On the other hand, that which we allow him to discover for himself will remain with him visible for the rest of his life.

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.

The more we try to improve our schools, the heavier the teaching task becomes; and the better our teaching methods the more difficult they are to apply.

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