In the philosophy of mind, non-reductive materialism is a position taken by people who are convinced that there are non-material properties, yet still want to maintain a monistic ontology, while distancing themselves from idealism. Generally, this position entails a substance monism combined with property dualism. So, there is one kind of substance in which physical and mental properties are both instantiated. A brain would then be composed of a material substance which has both mental and physical properties.
This view is usually combined with the thesis that mental properties supervene onto physical properties, but are not reducible to physical properties. So, any substance S that has mental property Q will have physical property P; and it is necessarily the case that if S has Q then is also has P. That is the general supervenience thesis held by non-reductive materialists who endorse property dualism.
There is a problem with this account of the mental, though. If there was a certain time in the past when there were no mental properties (a time before the existence of life complex enough to instantiate said properties), then there must be a time at which mental properties instantiated. It seems as though there’s literally a moment when mental properties didn’t exist, then they were ‘zapped’ into existence by whatever it was that instantiated the mental properties. It seems very implausible that such an account is true, given a monistic, materialist ontology. However, on substance dualism, the existence of non-material/non-physical properties like the ones endorsed by the property dualist is a plausible possibility. So, the moral of this story is that non-reductive materialism doesn’t seem as plausible as a substance dualism, given the existence of non-physical properties. If the materialist doesn’t find substance dualism plausible for the many reasons many philosophers of mind do, then the materialist may want to bite the bullet and give up his commitment to non-physical properties (unless he or she wishes to become a substance dualist).
My thoughts are re-printed below:
If I agreed that mental states had to “zap in” at some point in the past, then I would find this objection more appealing. That said, property dualism does not require that this occur. A more faithful property dualism would say, rather, that some form of “phenomenal character” existed at all points in the history of the universe, but this is not to say that it has to be recognizably “mental,” as we think of it today. The distinction between “physical” and “mental” is irrelevant to the discussion of property dualism—and philosophy of mind in general, I think, as everything mental is, so far as we can tell, necessarily physical is some way*—it is the distinction between objective and subjective that is most important. Each side of this more refined distinction has fundamentally different tools of explanation, and this is what I think of as a true property dualism.
*for support, I rely on a simple principle from Christof Koch: “No matter, never mind.”