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.

Play is the answer to how anything new comes about.

The most developed science remains a continual becoming

Logic and mathematics are nothing but specialised linguistic structures.

Moral autonomy appears when the mind regards as necessary an ideal that is independent of all external pressures.

In genetic epistemology, as in developmental psychology, too, there is never an absolute beginning.

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