St. Thomas Aquinas's Treatise on Human Nature occupies questions 75-102 of Part 1 of the Summa Theologiae. It contains St. Thomas's most mature statement of his philosophical and theological anthropology, i.e., his account of what human beings are and of their origin as distinctive creatures made in the image of God. This translation, moreover, is the only complete edition of all the material St. Thomas envisaged as being part of the Treatise.

The treatise begins with two long and complex questions on the metaphysical status of the human soul and its relation to the human organism. Here St. Thomas tries to show how the human being is both an animal and an animal who transcend the other animals. In doing so he marks out a distinctive Christian/Aristotelian conceptual space between "materialist" accounts of human nature that reduce human beings to mere collections of physical or chemical or biological components and "dualistic" accounts of human nature, such as those propounded by Plato and, later on, Descartes, that identify human beings with their immaterial souls.

The next thirteen questions deal with the powers of the soul, especially those higher intellective powers of understanding and willing that distinguish human beings from the other animals. Here we are given a philosophical framework for the findings of the human sciences.

Finally, the last thirteen questions have to do with human origins, the creation of the first man and first woman, the state of our first parents, and their status as beings created in the image of God. In essence, this is St. Thomas's philosophically attuned commentary on the parts of Genesis 1-2 that deal specifically with the creation of the human species. These thirteen questions, though an integral part of the Treatise, are not included in other translations of the Treatise on Human Nature.