Using Aquinas' proposal, this article tries to show the nexus between the intelligibility of Nature and the intellectual knowledge of Universals that we think, and that stricto sensu exist only as forms of singular things that are around us. For it, and based on the idea that Nature allows itself to be known because of its intelligibility per se, we try to show the solution that Aquinas delivers to the question for the metaphysical statute of the universals. Also, and because is a particular case of this medieval problem, since that links the finitude and contingency of the basic inclinations of human person with the universality of certain ethical imperatives, we will also treat the subject of Natural law, in accordance with the exposure of Aquinas' Summa Theologiae.