Jean Piaget father of the cognitive and human development psychology

"Knowing reality means constructing systems of transformations that correspond, more or less adequately, to reality."

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

"Accomodation of mental structures to reality implies the existence of assimilatory schemas apart from which any structure would be impossible."

"The self thus becomes aware of itself, at least in its practical action, and discovers itself as a cause among other causes and as an object subject to the same laws as other objects."