Abstract

In this paper, I investigate the nature of complex bodies, especially living things. I argue that a living thing’s complexity is fundamentally different from that of a machine, so that living things are substances, while machines are not. I further argue that the best way to understand the unity and complexity of a living thing is to follow Aquinas in holding that the elements and other parts are present in wholes by their powers, rather than as substances. I show that presence by power is not refuted by the discoveries of modern physics, and that it can help us understand the relations between parts and wholes in a more universal way which includes both living and non-living things.