 (1) According to the first theory, the human rational soul is a substance that is simple in its essence, in other words it has no parts. It is the same essence that vegetates, senses, and understands. The problem Kilwardby identifies in this theory is that the vegetative, sensitive and intellective potentiae are found in different kinds of beings: the vegetative is found without the others in plants, the sensitive without the intellective in non-rational animals, and the intellective without the other two in spiritual beings. But, if that is the case, how do they come to be one and a same simple essence in humans? The only way to sustain such a thesis would be to argue that these potentiae are equivocally said of humans and other beings; but that is manifestly false: if the objects and operations of the powers are the same, the powers and the potentiae in which they are rooted must also be the same. For example, in both humans and other living things the operations of the vegetative part of the soul are to take nourishment, generate, and grow. Therefore, the vegetative potentiae is the same in all living things and the sensitive is the same in all animals (E 5, 35–6). The problem is that if all three parts of the soul constitute one and the same simple essence, then