Plotinus roots the immortality of the soul in its immaterial nature. Body, he says, is the instrument of the soul, by which it acts, and is perishable. It is the the soul that acts, however, not the body, and so we, who are the agents, are the soul, not the body, which is merely our tool.
He suggests that it is absurd to suppose that a living thing can be composed entirely of non-living things. This is what is supposed by materialists, of course, for instance, Marxists, who suppose there is an “emergence” of new behaviors from sufficiently complex systems. I guess a materialist would take it to mean that no real explanation of life can be correct. This, she might suppose, depends on a faulty notion of explanation. The effect is always found already in the cause, and it only becomes, as it were, apparent to us in the course of the causal process. In any case, we are told by Plotinus that an aggregate of unintelligent things cannot be intelligent. Besides, even the simplest material thing has a soul, since it consists of form and matter—here the idea seems to be that a thing has causal activity, which can only be explained as due to soul, and it persists over time, which can only be explained by soul, and so on, and, of course, in each case the soul in question has the quality it supposedly imparts. Plotinus says no aggregation can form a one in sympathy with itself. Here it is suggested that to be in sympathy with itself it has to feel. I suppose we might say it has to have cognition to respond causally, and has to have cognition of itself to have sympathy with itself and hang together as one, and must feel to respond to itself causally. So A acts on B, B feels the action (and is aware of it), B responds to what it feels with its own action (which is adapted to what it is aware of).
Perhaps there are two different notions what an explanation looks like. One assumes that the presence of A is to be explained, I guess, by finding out where it’s hiding. I smell something, vanilla, so I look around for the vanilla. Perhaps its an ingredient in the cookies. So I know what produces that smell (its vanilla), but where is it? I know what produces actions (minds), but where is it? All I see are bodies, and that can’t be it. It must be hidden in the bodies. I suppose an atomist is not bothered by where the action producer is, for he thinks bodies move and interact of themselves. His worry is, why this action. That could mean, why is it falling? or it could mean, why this complicated action, i.e. its throwing the ball? It looks like a pretty complicated mess of organized stuff throwing the ball, so it must have something to do with how it is all organized, given the natural tendencies of its parts to their own more elementary actions, and its environment, to which it is responding, and . . . What are the prospects for getting real information out of this stuff? Well, I might be able to do something about the smell if I find its source, remove it, say, or enhance it. Or maybe knowing where there is some vanilla is important in some other way. Can I do something about mind if I find it hiding in a body? I suppose Plotinus thinks so, for I can recognize that it is the mind that acts, not the body, and so the mind is myself, and so I am immortal, my body and its needs etc. are alien to me in some way, and imposition on me, and so forth. What it won’t let me do is to explain why bodies with minds act the way they do, unless I see why minds act the way they do, and that is not explained at all. But maybe it is, if I take it minds are rational, perceptive, etc., and try to understand them as minds. Why does anything act like a mind? Well, some things are minds. Vanilla smells like vanilla, because that is an attribute of vanilla and it is vanilla. I suppose we could grant all that, and so grant that vanilla and minds really exist and are to be found where we find them, and still leave open how to explain (1) how such things arise, (2) why such things behave the way they do (like vanilla or minds), (3) how this sort of thing came to exist (evolution? Evolution of chemical elements, arising of an environment in which vanilla is stable, evolution and the arising of an organism that produces that odoriferous product). Plotinus stops us before we can do this sort of explanation for minds, and tells us that minds are simple and without parts, so it can’t be done. Minds have a given set of properties that just belong to them, as electrons do, say. How does he know minds are simple and without parts? I think Kant had real insight into this. We project the unity of apperception onto the mind that enjoys it. We appear simple to ourselves, and this appearance can only be explained if the one to whom it appears is simple.
So if I ask, what is a mind?, and decide there aren’t any such things, that is because I’ve decided that a mind is not a simple thing, or cannot be identified as some (simple, or complex) component of a person (even if persons do “have minds”) in the way that the components explain why the thing composed of them behaves as it does. (For instance, the components or a radio—if one is defective, the radio won’t work, so I can replace the component and that will repair it. Can I replace the mind, or provide one where it is the (only) thing that is missing, and so make a functional person? I would need the components, some way in which they are related to one another to make up the composite (so I can replace them, say), so that a person would consist of a mind and a body—combined how? No theory of that sort works at all well, so minds are not a component of persons, even if persons have minds, just as my ability to read Latin is not a component of me, even if I have that ability. Maybe the Stoics asked how the two might be combined, and decided, sensibly enough, that they would have to be in the same place. That means mind must be some special sort of body, located in the same place as the perceptible body.
If we imagine an aggregate of things that in fact (in a given environment) behaves like a rabbit, like it is accomplishing the intentions of a rabbit, recognizing and desiring carrots, and so on, is it really recognizing carrots? We want to say that we have only contrived things so that it appears to do so, or imitates carrot recognition behavior closely. But (1) in order to be able to explain why it behaves like this, we have to make some such move, constructing a machine that behaves the right way in certain circumstances, (2) tellingly, the rabbits we actually encounter break down and stop acting like rabbits under odd circumstances, which suggests that we are dealing with precisely such machines (and this thought can be pursued with a great deal of detailed investigation, getting clues as to the construction of the machine from an examination when it stops working right, which mesh with studies of things needed to construct the machine (nutrition studies, say), mechanisms by which the machine is built (embryology etc.), and evolutionary theory, connecting this machine closely to a lot of others. . .) The cumulative evidence here seems to be overwhelmingly in favor of the machine hypothesis.
But say we go ahead, and postulate it is really a rabbit. Then there is something that makes it act like a rabbit (is responsible for its being that sort of machine). This might be a designer with the concept of rabbit (at least this can work in the case of an adding machine, or a mechanical rabbit). Or it might be some evolutionary consideration, i.e. the more it acts like a rabbit the more like it is to produce machines similar to itself that will persist, and so we see how being like a rabbit contributes to the arising of machines like rabbits. Perhaps neither of these two explanations requires that we postulate a real rabbit, or perfect rabbit concept? This would be so, in particular, because the postulating of a rabbit concept or design entails postulating a concept-possessing thing, which turns out to be explainable only if it is assumed to be a machine that acts more or less like such a thing (a concept-possessor), for one of the two reasons just given. Or it means postulating an environment in which evolution occurs (and the theory of evolution, too, is an idealization, so it only occurs in that environment more or less).
The problem here is that we assign the perfect, idealized conception a causal role. It produces the rabbit behavior. So if it is a concept, or a description of an evolutionary selected for strategy, it can do that. Except that we ask how it can do that, and we find ourselves back at the machine model and functionalism again. In the end we are projecting onto a mechanical system (and, of course, the system really does allow that projection (select for that sort of behavior in a perceptive animal), so it is not uninformative about it by any means that we can project on it in this way). Only if a real, ideal rabbit produces the behavior, is the rabbit a real rabbit, then, and concepts or evolution (of substantial forms?) etc. only provide what we need if they are ideal cases.
But explanation has to start somewhere, with the unexplained. True enough, and always (? maybe I should only say “usually”) it has to start with the attribution of an ideal conception to the world, without explanation as to how it has happened that such an attribution can be made. Often, looking at the practicalities, we find that the ideal concept, or evolutionary strategy, or mind, is a good place to start. That is, to begin an investigation here how the thing is possible means changing the subject, the beginning of a new investigation entirely. Now we are going to do philosophical semantics rather than chemistry, or now we are going to do philosophical psychology, rather than explaining why Bill did that to his sister. It is at such switching points that we are most likely to imagine that the real ideal must be present and operative, or to imagine that this is what we must presuppose (else we have to launch on that new investigation), particularly if we are not at all accustomed to the new sort of investigation to be launched, so that we cannot see how to go about it. This is what Plotinus complains about in IV 7, he just can’t see how even to start constructing a machine with unity of apperception or self-knowledge from material parts. So our practical decision to stop here hardens into an a priori necessity to stop here. And then we can draw some interesting conclusions, and the soul turns out to be inconstructible, indestructible and immortal. But none of that—this is just a practical decision to limit the range of our investigations. The world is such, perhaps, as to justify that decision, but nothing interesting about the world follows from that. Certainly the impossibility of proceeding further should we decide to does not follow, but only its relative difficulty, or inadvisability, or some such thing.