A faction in the social sciences founded by Maturana and Varela. It's similar to constructivism in the field of cognitive psychology, but goes a step further down to the underlying philosophy. The main idea is that we can only see what happens inside the brain, and we don't know everything about the outside. But radical constructivism is different from solipsism because it doesn't deny the existence of a world outside the brain. It only denies the possibility of gaining exact knowledge about this world, because all we have is the perpetuation of the brain as closed, homeostatic system, from which it constructs the world we know.