There are degrees of commitment to an Aristotelian metaphysics. The most basic form
of Aristotelianism involves accepting things, rather than events, as causes, and attributing
their causal activity to their possession of properties that are by nature causal powers. This
rules out a conception of laws of nature as simple descriptions of regular patterns, and the
claim that being a cause or an effect results from fitting in to some universal pattern. A
more specific form adds that claim that things are sorted into natural kinds by their
fundamental causal powers; a yet more specific form asserts that the properties that make a
thing belong to a given natural kind are possessed necessarily by that thing, and constitute
its essence. Scientific investigation, on this view, proceeds by discovering the causal
powers that are associated with things of a given kind, and laws of nature, in science,
amount to statements about the causal powers possessed by different kinds of thing. More
specific still is the assertion that the essence of a thing is its substantial form. This claim is
as specific as current neo-Aristotelianism gets; the Aristotelian doctrines of hylomorphism
and final causes are rarely defended by current neo-Aristotelians, and will not be construed
as forming part of the broadly Aristotelian metaphysics discussed in this paper.