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I'm having trouble following this. According to traditional theology, the bifurcation occurs every time someone dies -- that is, the soul separates from the body.

True. The unity of body and soul is ultimately mysterious and very difficult to explain positively. I prefer a negative proof. That is: all other categorizations of the human person end in contradiction and incoherence.

The Catholic position is that the human person is body/soul. Each have different powers yet are fully united.

The following explains the tension:

The summary so far given merely says what the Aristotelian-Thomistic theory is not. It is harder to explain what this (non-Lockean) identity really amounts to and why one ought to believe that Aquinas and Aristotle are right in their theory. The main point in favor of this theory of knowledge is the recognition that both sense knowledge and intellectual knowledge are activities that we engage in. In opposition to the Lockean view, where sense impressions are things that we suffer and undergo, Thomas and Aristotle claim that this is not the essence of sensation, although both admit that there is a passive element in the organs when they are passively affected by the sense object. Thomas and Aristotle believe that sensation is an activity that remains in the one who senses, and is not an activity that passes from an object to the organ. Thus, Aquinas calls it an immanent activity (as opposed to a transitive activity- like the heating of water). Aristotle says that it is a kind of being acted upon or motion, but one that should receive its own name. Like transitive actions, e.g. the heating of water, something receives a new form as the water receives the form heat from the fire. However, in such cases, the form of heat in the water is not the same as the form of heat in the fire, but only the same in kind, being in different parts of matter. Moreover, in the case of the heating of water, the water loses the form that it had before, namely the form of coolness. In the case of sensation, these features do not obtain: the reception is not of a similar form, but of the SAME form; and the reception does not involve the destruction of the pre-existing form, but does involve the fulfillment and completion of the knowing power; and thus, the reception is not into matter, but a kind of immaterial reception. Thus, the knower becomes one with the known, because it IS in a new way, i.e. with the very same form of the thing known, and this happens in an immaterial way that fulfills the knower. What I've said about sensation works the same with the intellect, but the identity is such that it occurs even without an organ, and thus the intellect is immaterial in an even stronger sense than the sense powers.
The Aristotelian-Thomistic account, then, neatly sidesteps indirect realism/phenomenalism that has plagued philosophy since Descartes. It claims that we directly know reality because we are formally one with it. Our cognitive powers are enformed by the very same forms as their objects, yet these forms are not what we know, but the means by which we know extramental objects. We know things by receiving the forms of them in an immaterial way, and this reception is the fulfillment, not the destruction, of the knowing powers.
The theory is not without its problems and it is not entirely clear that it accords with other things we know about the world, because as a corollary to the theory, Aristotle and Thomas seems to be making the claim that what really happens in perception is nothing that can be empirically verified in the way other material interactions can be verified. Precisely because perception is an immaterial, immanent action, it is of a different kind than transitive actions, which is what their theory would claim scientific observation can detect. Thomists tend to believe that such a consequence is not fatal to the viability of this identity theory since they would also claim that the very life of living things cannot be totally explained, as modern science tries to do, by appealing only to microscopic parts in interaction (bio-chemistry). And yet it seems a matter of intuitive experience that an organism is more than the parts working together (for an organism that has just died has all the same parts). Thus, although modern chemistry and biology no doubt make true and illuminating observations about some of the mechanisms by which living things live and have perception, that sort of explanation does not totally capture the whole of what it means to live and perceive. Thus, the appeal to souls and immaterial reception of form is an irreducible and ineliminable source of explanation.