St. Thomas Aquinas on the presence of the elements in living substances

Aristotle, explains the physical world, the world of material substances which are in motion, which are born, and which grow. The understanding of the natural world as set forth by Aristotle especially in the first two books of the Physics should give rise to several questions in the mind of one even somewhat familiar with the modern scientific account of the natural world. One of these, and one which must be answered if form and matter are accepted as principles of the natural world, is how the diverse atoms and particles of modern science relate to form, the specifying principle of the material thing, and matter, pure potentiality without form or properties according to St. Thomas.; The main problem which this dissertation investigates is this: How can a living thing, which contains a great diversity of elements, be really one substance? At one and the same time, we are sure that living things are composed of the elements and that a living thing is really one thing. If the elements are substances, then the living thing is only an aggregate and not really one. On the other hand, if the thing is a substance, it is not clear how elements can be present in it. Presence by power, which St. Thomas uses to explain the presence of elements not only in complex inanimate things, but also in living things, solves this problem. The elements are present in the living thing (and in any complex thing) by their powers, but their substantial forms are not actually present. Thus the living thing is one, made both to be and to be one by its soul, yet it still contains the elements, but not the substantial forms of the elements, and thus is only one thing.; After laying out the basic doctrine of presence by power as developed by Aquinas, this dissertation discusses his use of presence by power in living things. Presence by power is compared with the theories of atomism and multiplicity of substantial forms and defended as the best explanation of the way in which the elements are present in living things.