Plato considered that only the mind could access the timeless reality of truths, the realm of the Forms casting the visible world. Plato's metaphorical allegory of the cave—whereby humans only know reality as shadows of the real things they see interacting on a wall—suggests the practical consequences of Platonic realism as to "natural philosophy" in its endeavor to explain the natural world and as to values in human society. (Value theory comprises ethics, aesthetics, and political philosophy.)