Is Prime Matter Energy?

This paper tests the hypothesis that the prime matter of classical Aristotelian-Scholastic metaphysics is numerically identical to energy. Is P = E? After outlining the classical Aristotelian concept of prime matter, I provide the master argument for it, based on the phenomenon of substantial change. I then outline what we know about energy as a scientific concept, including its role and application in some key fields. Next, I consider the arguments in favour of prime matter being identical to energy, followed by the arguments against this. The method used is that of ontological profile comparison: does the profile of prime matter match, in key features, that of energy? An affirmative answer, that P = E, would be a momentous discovery: it would show that one of the most neglected and derided ideas of pre-modern metaphysics-a contributor to its downfall in the wake of the Scientific Revolution-was correct all along. From a negative answer, we would still learn much about the interaction of science and metaphysics. It turns out, however, given what we currently know, that the answer is not quite as simple as one might hope.