In his word physics, things are in constant flux and are observable through our senses. In the intelligible world the forms are eternal and immutable and are apprehended through reason and not through the senses. His argument for the existence of forms is similar to the allegory of the cave where forms are actually the only real thing while the physical world is just a reflection of the forms. Just as in the allegory, the observations were misleading interpretations of the shadow of the real