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

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.

Logical reasoning is an argument which we have with ourselves and which reproduces internally the features of a real argument.

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.

Logical activity is not the whole of intelligence. One can be intelligent without being particularly logical.