Play is the work of childhood. - Jean Piaget

Thus arises the second tendency, which consists in regarding logical and mathematical relations as irreducible, and in making an analysis of the higher intellectual functions depend on an analysis of them. But it is questionable whether logic, regarded as something eluding the attempts of experimental psychology to explain it, can in its turn legitimately explain anything in psychological experience.

Knowing reality means constructing systems of transformations that correspond, more or less adequately, to reality. They are more or less isomorphic to transformations of reality. The transformational structures of which knowledge consists are not copies of the transformations in reality; they are simply possible isomorphic models among which experience can enable us to choose. Knowledge, then, is a system of transformations that become progressively adequate.

There are no really solipsistic philosophers, and those who think they are deceive themselves. The true solipsist feels at one with the universe, and so very identical to it that he does not even feel the need for two terms. The true solipsist projects all his states of mind onto things. The true solipsist is entirely alone in the world, that is, he has no notion of anything exterior to himself. In other words the true solipsist has no idea of self. There is no self: there is the world. It is in this sense it is reasonable to call a baby a solipsist: the feelings and desires of a baby know no limits since they are a part of everything he sees, touches, and perceives. Babies are, then, obviously narcissistic, but not in the way adults are, not even Spinoza's God, and I am a little afraid that Freud sometimes forgets that the narcissistic baby has no sense of self. Given this definition of solipsism, egocentrism in children clearly appears to be a simple continuation of solipsism in infants.. Egocentrism, as we have seen, is not an intentional or even a conscious process. A child has no idea that he is egocentric. He believes everybody thinks the way he does, and this false universality is due simply to an absence of the sense of limits on his individuality. In this light, egocentrism and solipsism are quite comparable: both stem from the absence or the weakness of the sense of self.