Thomas Aquinas

===Psychology and anthropology===
Thomas Aquinas maintains that a human is a single material substance. He understands the soul as the form of the body, which makes a human being the composite of the two. Thus, only living, form-matter composites can truly be called human; dead bodies are "human" only analogously. One actually existing substance comes from body and soul. A human is a single material substance, but still should be understood as having an immaterial soul, which continues after bodily death.

In his ''Summa Theologiae'' Thomas states his position on the nature of the soul; defining it as "the first principle of life".<ref>{{Cite book |title=Summa Theologiae of St. Thomas Aquinas |last=Aquinas |first=Thomas |year=1920 |edition=Second and Revised |translator-last=The Fathers of the English Dominican Province |chapter=Question 75, Article 1}}</ref> The soul is not corporeal, or a body; it is the act of a body. Because the intellect is incorporeal, it does not use the bodily organs, as "the operation of anything follows the mode of its being".<ref>{{Cite book |title=Summa Theologiae of St. Thomas Aquinas |last=Aquinas |first=Thomas |year=1920 |edition=Second and Revised |translator-last=The Fathers of the English Dominican Province |chapter=Question 75, Article 3}}</ref>

[[File:Luis muñoz-santo tomás de aquino.jpg|thumb|right|Saint Thomas Aquinas by Luis Muñoz Lafuente]]
According to Thomas, the soul is not matter, not even incorporeal or spiritual matter. If it were, it would not be able to understand universals, which are immaterial. A receiver receives things according to the receiver's own nature, so for the soul (receiver) to understand (receive) universals, it must have the same nature as universals. Yet, any substance that understands universals may not be a matter-form composite. So, humans have rational souls, which are abstract forms independent of the body. But a human being is one existing, single material substance that comes from body and soul: that is what Thomas means when he writes that "something one in nature can be formed from an intellectual substance and a body", and "a thing one in nature does not result from two permanent entities unless one has the character of substantial form and the other of matter."<ref>{{Cite book |title=Summa Contra Gentiles |last=Aquinas |first=Thomas |publisher=U. of Notre Dame Press |year=1975 |location=Notre Dame, Ind. |translator-last=Anton C. Pegis |chapter=5 volumes. |display-authors=etal}}</ref>