Is Thomas Aquinas an inconsequential materialist or a bad cartesian?

Aquinas holds that soul and body are substantially united as form and matter, following Aristotle. At the same time, he asserts that the human soul is subsistent. This position has been criticized as incoherent. Some argue that St. Thomas is an inconsistent materialist, for the internal logic of hylomorphism should have led him away from dualistic theses. Others, like Swinburne, claim that Aquinas is a substantial dualist, whose thesis would be very close to that of Descartes. We respond to these two positions by showing that the thomistic answer is coherent and realistic.