 Kilwardby’s theory of the soul is formulated around the central conceptions of unity and composition, rather than those of unicity and simplicity. According to Kilwardby, “all composite things have unity, even though they do not have simplicity” (E 6, 47), meaning that complexity is not incompatible with unity, only with simplicity. What is required in addition is only a principle strong enough to justify the unity. He thinks to have found it in what we could call ‘the principle of ordination’: a substance can be composite and nevertheless one when the essentially different parts are ordered to each other (ad invicem), from the less to the more complete. A human being has “one form which is not simple (simplex) but a composite of many [potentiae] having a natural order to each other” (E 7,  53).[4]  These forms are organized in a hierarchical structure so that there is one which is the perfection of the whole composite. In the case of human beings, that last completive form is the intellective soul.