Reddit reviews Real Essentialism (Routledge Studies in Contemporary Philosophy)

One objection that can be raised against full-blown Cartesian dualism, with a material, mechanical body interacting with an immaterial soul, is that it seems to violate the law of conservation of energy, since for the body to act upon the soul or the soul to act upon the body would require a transfer of energy in or out of the material universe.

But I don't know if you can make the hylemorphic conception of the soul understood without first explaining how everything is a union of matter and form. We don't live in a universe made up only of matter with we humans having something extra called a soul, everything has a form and the soul is ours. Edward Feser builds up from this metaphysics to the existence of the soul in The Last Superstition, with competing views attacked in the last two chapters. For arguments at a more academic level, check out the work of David S. Oderberg, particularly "Hylemorphic Dualism". If you're in it to win it, see Oderberg's monograph Real Essentialism, or Feser's Scholastic Metaphysics: A Contemporary Introduction, which has apparently made Stephen Mumford realise he was a Scholastic realist without knowing it.

I know that few will thrill at the prospect of studying metaphysics at that level, but I do think it's important for evangelisation since so much unbelief proceeds from this fiction that what happens at Mass, for example, could in principle be more accurately described in terms of chemical interaction between atoms without reference to abstractions like religion, history, music, or people. So for those of you who are still discerning, please think about a vocation as a philosopher.

And a defense of it. And a defense of new essentialism.

Per Aristotelianism/Aristotelian-Thomism, there are four causes to a thing-- the efficient cause (from which a thing comes), the material cause (out of which a thing comes, the matter), the formal cause (into which a thing comes, the essence of a thing-- what means to be x), and the final cause (a thing produces x,y,z effects over a,b,c). The middle ones are part of what is called "hylemorphism", or hylemorphic dualism. Basically, for Aristotle a substance was a marriage between form and matter through motion (a reduction from potency to act, change).

Of course, there are more less perfect instantiations of an essence, degrees in which a universal is fulfilled. See "Metaphysics" by Loux, as well as some of the many, many problems that come from denying formal and final causes in Edward Feser's "The Last Superstition". Real Essentialism by David Oderberg also gives a contemporary defense of essences.

Natural law theory generally states, and this is very brief (as is the case for any moral theory-- I couldn't exactly give you every particular of, say, Kantianism in a short post), that as rational agents are culpable in violating formal and final causes, that is to say that they are blameworthy for creating a "bad" instantiation of an essence, or violating a final cause.

But of course, even if natural law were be wrong, moral relativism cannot be correct. I'd recommend picking up those books listed, Metaphysics, The Last Superstition (as well as Feser's Philosophy of the Mind intro and Aquinas intro), and Real Essentialism.

Yes, Thomism has never gone away, it was never successfully argued against, as the major player it was simply abandoned for a mechanical philosophy due to the success of Newtonian/Descartian science which has itself now been abandoned to a certain degree with quantum physics.

Papers and books are still being published from a Thomistic viewpoint.

One example:
http://www.amazon.com/Essentialism-Routledge-Studies-Contemporary-Philosophy/dp/0415323649