Who are some modern philosophers that argue for either dualism or the idea that mind is a nonphysical substance?

By "modern philosophers" I am assuming you mean contemporary philosophers. (We philosophers use "modern philosophers" to refer primarily to European philosophers from roughly 1600-1900, and among that group there are a number of substance dualists, including Descartes, Malebranche, Leibniz, and arguably Kant).

Among contemporary Western philosophers, there are not that many substance dualists, though it is making a bit of a comeback recently. Of note are E.J. Lowe, Richard Swinburne, and (I think) Alvin Plantiga. I am likely leaving out others. There is an even bigger resurgence of "property dualists", people who argue that the universe consists of just one kind of substance, but all (or some) of that substance has both physical properties and mental properties. David Chalmers played a big role in motivating this position. Recently, Susan Schneider (if I understand her correctly) has argued that you can't be a property dualist without accepting substance dualism.

The dominant position in philosophy of mind is physicalism (the view that everything that exists consists of stuff that can be described in the language of natural sciences), and among the physicalists there are reductive physicalists and non-reductive physicalists. But I won't drone on any longer about all this!

This SEP entry on dualism may be of interest: http://plato.stanford.edu/entries/dualism/

Here's another contemporary philosopher you might want to look into: Galen Strawson--

"I take physicalism to be the view that every real, concrete phenomenon in the universe is physical. …[O]ne thing is absolutely clear. You're…not a real physicalist, if you deny the existence of the phenomenon whose existence is more certain than the existence of anything else: experience, 'consciousness', conscious experience, 'phenomenology', experiential 'what-it's-likeness', feeling, sensation, explicit conscious thought as we have it and know it at almost every waking moment. … [E]xperiential phenomena 'just are' physical, so that there is a lot more to neurons than physics and neurophysiology record…." (Strawson, Galen (2006), Realistic Monism, in A. Freeman (ed.), Consciousness and Its Place in Nature (Exeter: Imprint Academic))

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