Dualism is a failure to get to the fundamental truth of things, but it also requires that one actually posits two things, that is, that he posits multiple principles or explanatory schemes in the same genus.
There is, for example, a real dualism in our explaining one sort of phenomena by Relativity and another sort by QM, or in having more than one physical law or theory, or in positing a good and evil god or a good and evil will to account for natural or human actions. We know a priori from the mere duality of these things that they cannot be final but point to some ultimate unification.
But positing matter and form as principles or material and immaterial agents as sources of action lacks this defining characteristic of dualism. Aristotle came up with the idea of matter and form while also denying there was any common genus for the active and passive, and his category “substance” does not include material and immaterial agents. Complaints about so-called Cartesian dualism therefore confuse the sort of dualism which needs to be transcended or compressed with an ontological division that is not a bona fide dualism at all, but only a trick of the imagination that there is some homogeneous category for matter and form, the physical and spiritual, or the creature and creator.
Briefly, there can be no dualism in principles of being because being cannot be dual. It has no genus, nor can beings or existents be counted, still less be two. You can count the books or shades of blue on your desk, but not the beings.
Just Thomism 
Rchard E. Hennessey said,
February 23, 2016 at 3:26 pm
I have assumed for decades that the the books on my desk and scattered around my office are beings, albeit artificial beings. I also assumed that, just because they are beings, they, e.g., must either be or not be but cannot both be and not be, in any one respect and at any one time Now you are telling me that they are not beings. Will you go on to tell me that they are not subject to those principles?
James Chastek said,
February 23, 2016 at 5:42 pm
You can count colors, inches, relations, powers, masses, weights, volumes, temperatures too, since they all exist. But if someone asks you to just count existents, there is no in-principle way to know where to start or when you would be done. It would be like trying to count quantities with no unit.
What you were doing with your books was counting beings simpliciter, but there is more to being than that. Accidents exist too, for example. And beings of reason would take us immediately into the uncountable infinite.
Rchard E. Hennessey said,
February 24, 2016 at 7:23 am
I think I am satisfied with your recognition that what I was doing with my books was “counting beings simpliciter,” though it is not clear to me just what the import of the qualification, “simpliciter,” is here.
Yet I still puzzle over the “still less be two,” of your statement, “It [being] has no genus, nor can beings or existents be counted, still less be two.” For it seems to me, e.g., assuming the existence both of Richard Hennessey and of God, that the conjunction:
Richard Hennessey is one being or existent, God is one being or existent, and Richard Hennessey is not God.
is true if and only if
Richard Hennessey and God are two beings or existents.
Brandon Watson said,
February 24, 2016 at 10:42 am
But this gets into absurdity almost immediately. Richard Hennessey’s hand is also one being or existent, and Richard Hennessey is not His hand; therefore you get ‘Richard Hennessey and his hand are two beings or existents’. And Richard Hennessey’s freckle (say) is a being, and Richard Hennessey is a being, and Richard Hennessey is not a freckle; therefore Richard Hennessey and his freckle are two beings. And Richard Hennessey today is a being and Richard Hennessey yesterday is a being and Richard Hennessey today is not Richard Hennessey yesterday, so Richard Hennessey today and Richard Hennessey yesterday are two beings. So how many beings are you?
The obvious reason for the absurdity is that ‘being’ is not a uniform unit for counting; things are beings in different ways. One might as well be treating fruits and colors and tastes by a single unit: The red apple with a green spot, with sweet flesh and bitter seeds, then is one apple, one red, one green, one sweet, three bitter. What number of beings? Seven! But in reality, of course, we’re not counting beings, we’re counting uses of words.
Rchard E. Hennessey said,
February 25, 2016 at 11:45 am
The aforementioned Richard Hennessey and his hand are two beings, albeit beings of two different kinds. No absurdity there. The sweetness of an apple and the redness of its overall cover are two distinct beings, specifically two distinct beings of two different categories. Again no absurdity.
Continuing with the apple: It seems that you have actually begun the counting of the apple and its accidents, having counted the apple itself, its redness, the greenness of the spot, the sweetness of the flesh, the three bitternesses of the seeds. You could have continued, counting, say, its various spatial relationships, beginning with the ones it has to the various other apples on the same tree and then to the other apples on other trees in the same orchard, etc.. I grant you the point that you’ll never complete the counting. That happens. But you did get started.
Is the issue the fact that I am taking the being, which the beings I say are countable all “have in common,” is sufficiently homogeneous to make counting possible?
Brandon Watson said,
February 25, 2016 at 4:48 pm
Saying that Richard Hennessey and his hand are two beings is a category error — a paradigmatic case of one, actually — so, yes, it is entirely absurd. For instance, it commits you to claiming that nothing that touches the being that is Richard Hennessey’s hand touches the being that is Richard Hennessey (because they are two different beings, not one). Likewise, it commits you to claiming that, since Richard Hennessey not including such-and-such hair is different from Richard Hennessey including that hair, that there are thus two Richard Hennessey’s. These are the kinds of things that everyone recognizes as quite obviously absurd. You can’t even get started with it; it’s obviously incoherent from the beginning. But even if we assumed that you could get started, we run right smack into an absurdity, immediately: it requires you to claim that the only number of everything is infinite (or at least so large as to be practically indistinguishable from infinite). Suddenly, there are not two cats on the mat; there are infinite cats on infinite mats. There is not one Richard Hennessey, there is an infinite number — Richard Hennessey today, Richard Hennessey two nanoseconds ago, Richard Hennessey except for the color of his eyes, Richard Hennessey not counting his left side, etc., etc.
What you actually seem to be doing in all these cases is counting possible uses of the word ‘being’; that’s a very different thing from counting beings. (Conflating them would be another category mistake.)
holopupenko said,
February 24, 2016 at 11:14 am
See Chapter I – Transcendentals, Article II – Unity in *Elementary Course in Christian Philosophy by Brother Louis of Poissy: https://www3.nd.edu/~maritain/jmc/etext/cp21.htm.