Aristotle (and later the Scholastics) considered the soul to be the form of the body. But back then, though many changes of the living body could obviously be observed (considered to be “accidental changes”), what is possible today was unknown.

If somebody gets an organ transplant, we still consider him to be the same person. This is also true with rare multiple organ transplants – in one case the stomach, gall bladder, bowel, pancreas, and liver were successfully transplanted.

How can this still be reconciled with the supposed existence of a cohering form of the body which can be identified with “soul”?

It seems at least if medicine / technology could advance to extremes like the cyborgs in Ghost in the Shell or successful brain transplants, this would constitute a nearly decisive counterargument. Where did the soul end up? If we don't fall back on “the soul is the form of the brain”, we might as well say that the soul can be split apart.

  • Are you asking how scholastics would interpret soul's endurance through massive body changes, or how it works on the modern understanding of "form"? According to Aristotle, Aquinas, etc., soul, although inseparable from the body, has independent causal powers, so it is not a "form" in the modern epiphenomenal sense. On modern functionalist view, "soul" is indeed a "form" (dynamic structure) supported by the brain, and it can be realized on other material carriers, although not disembodied. But then Ghost in the Shell's Major is not a problem, even when she "dives" into the net. – Conifold Oct 20 '17 at 22:47
  • @Conifold definitely the first! Ok, let's take the most extreme example: brain-swapping transplant. If that would be possible, we would obviously believe that the seat of personality is where the brain is, not where the larger part of the body is. And the intuitive pressure to somehow make some link between personality and the soul is just intense. – viuser Oct 21 '17 at 6:26
  • IF the soul is the form of an orgnism, why the "removal" of some parts of it (the organism grows and changes unceasingly) must affects the soul ? Form is not a sort of "shape". – Mauro ALLEGRANZA Oct 21 '17 at 12:34
  • @MauroALLEGRANZA removing an organ counts as “removal” – but at some point it seems more like a splitting of the body. – viuser Oct 21 '17 at 22:06
  • @MauroALLEGRANZA and do you think the brain is just like any other part of the body? Like the spleen? – viuser Oct 21 '17 at 22:47

The notion of "form", just as the notions of "cause" and "matter", changed very significantly since the middle ages. Pasnau's Chapter on form and matter, and last two chapters in Kenny's Aquinas on Mind (both freely accessible) are good sources on the Aristotelian views of form.

According to Aristotle, form is what brings matter, the potentiality, to actuality. Aristotle applied this to everything from shapes to souls, and scholastics followed him, e.g. Aquinas defines soul as "the first principle of life in living beings... not a body, but an actuality of a body, just as heat, which is the principle of heating, is not a body, but a certain actuality of a body". And like Aristotle, he likens soul of the body to the unmoved mover of the cosmos. So this is not the kind of form we associate today with a supervenient "shape". Even replacing the whole body piece by piece, like the ship of Theseus, would not be an obstacle to keeping its soul more or less intact. Nor is this soul specifically attached to the brain, here is from Aquinas's Summa Theologiae:

"A substantial form is the form not just of the whole, but of every one of its parts. Since a whole is made up of parts, if the form of the whole were not what kept in existence the particular parts, it would merely be a pattern or structure, like the design of a house; and such a form is an accidental rather than a substantial form. But the soul is a substantial form, and hence it must be the form and actuality not only of the whole but of every part. That is why when the soul departs, what is left is not a human or an animal any more, except by a figure of speech, in the same way as a picture or a sculpture may be; and the same holds, as Aristotle says, for hand and eye and for flesh and bone. This is exhibited in the fact that no part of the body continues to function after the soul has departed". S1, 76, 8

Thus, the relation between the soul and the body parts is asymmetric, the parts are accidents which can be removed and/or replaced without affecting the soul, while it would not work the other way. Moreover, not only is the soul independently active it is also self-subsistent:

"The intellectual principle, therefore, which is called mind or intellect has its own activity in which the body has no share. But nothing can act on its own unless it exists on its own; for only what exists in actuality can act, and the way it acts depends upon the way it exists. Hence we do not say that heat heats, but that the hot body heats. So the human soul, which is called the intellect or mind, is something non-bodily and subsistent". S1, 75, 2c

This does not mean, however, that the soul can be seamlessly disembodied, "the soul, since it is part of the body of a human being, is not a whole human being, and my soul is not I; so even if a soul gains salvation in another life, that is not I or any human being". Of course, from the modern point of view Aristotelian "form" is badly equivocal in conflating shapes and souls. Aristotle himself had four causes without prioritizing efficient ones, their prominence is traceable to the success of modern science and its (efficiently) causal laws. But while the "shape" sense is relatively unproblematic today, the causal sense of form requires something very much like the downward causation from global to microphysical states, a toll order. This is noted by both Kenny and Pasnau:

"In Aristotle, these two aspects of form – proto-scientific and metaphysical – exist side by side, so that sometimes forms are conceived of on the model of souls, where souls are thought to have certain causal powers, whereas at other times forms are conceived of as abstract, functional principles, offering explanations at a level that is quite independent of whatever causal, physical story might be told about the natural world." (Pasnau)

"The substantial form in a human being may likewise be introduced as being, truistically, that by which a man is a man, or that which makes a man a man. In each of these cases the ‘makes’ is the ‘makes’ of formal causality, as when we say that it is a certain shape which makes a piece of metal a key... If the soul is a form in this sense, then it is no more a concrete object than a shape or a structure is. But besides the abstract notion of form, there is a notion of form as an agent. In these passages it is clear that Aquinas thinks of the human soul as being causally responsible for the various activities which make up a human life." (Kenny)

There was one issue discussed by scholastics that may have a bearing on the OP question, the issue of change in death. The form is supposed to be unchangeable, it is matter that changes in form-matter composites, or put differently, only the accidental part of the form. So what happens to the form of the body when its "principle of life" departs? To answer some postulated multiple substantial forms, which fueled the debate between unitarians, like Aquinas, and pluralists, like Ockham. The latter posited three distinct substantial forms within a human being: a rational soul, a sensory/nutritive soul, and the "form of corporeality", which makes the body "bodily". Here is Pasnau:

"The animal is a single substance, then, and it goes out of existence when it dies, but nevertheless part of it endures, in virtue of its corporeal form. A unitarian must instead say that when a substance goes out of existence, it wholly goes out of existence. Thus when an animal dies, not only is the corpse not that same body, but nothing about that corpse is the same. The corpse may have qualitatively the same properties, but those properties are numerically distinct. It was this implausible consequence – and the difficulty of explaining why a numerically distinct corpse should happen to have the same properties as the living body – that fueled the philosophical opposition to unitarianism."

  • Thank you. But the main point is still not addressed, which is more like an intuitive counterargument rather than an airtight logical contradiction. It may be a cultural prejudice to associate thinking, will, emotion, personality, consciousness, character etc. far more with the soul than, say, digestion, circulation, breathing, etc.. … – viuser Oct 25 '17 at 5:32
  • Still, if, after “brain swapping” had been performed, and we in our metaphysics would then have to conclude that Marc remained Marc with Marc's soul (only with Peter's brain) and the other way around – it's extremely hard to escape the conclusion that our usage of “soul” is quite Pickwickian. This objection can be dodged by claiming that such a transplantation would be metaphysically impossible, sure, but should we bet on that? – viuser Oct 25 '17 at 5:38
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    @wolf-revo-cats Aquinas argues that although Socrates's soul is incorruptible, separated from his body it is no longer Socrates, and the resurrection will have to include bodily resurrection, see Human Identity and Immortality. So neither Marc nor Peter may remain Marc or Peter under your scenario, even if we assume that souls traveled along with brains. But metaphysical identity is a separate question from whether one can fairly identify souls with Aristotelian forms. – Conifold Oct 25 '17 at 19:28
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    @wolf-revo-cats This last issue was the main motivation for introducing the form of corporeality separate from the soul. But that will not generally solve the ship of Theseus problem, and we know from biology that all matter in our bodies is replaced multiple times in the course of life. But identity through change puzzle goes back to entering Heraclitian river twice, Parmenides, Zeno, etc. Aristotle's form was introduced exactly to be the rock-in-the-flux for science to study. Its appropriation for ethical and religious purposes, started already by Aristotle, was perhaps a stretch too far. – Conifold Oct 25 '17 at 23:28
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    But I am not sure that substance dualism is much better. Yes, it has no problem with identity but instead we get a host of other problems. How exactly does eternal non-spatiotemporal soul connect to perishable spatiotemporal body? What is it "made of", what laws govern that stuff, etc.? One solution is to hold that the issues of personal identity, while important to us, are not metaphysically salient. We can trace souls/forms through transformations scientifically, but whether they are identifiable with persons depends on pragmatic considerations (obviously, this won't work for theologians). – Conifold Oct 25 '17 at 23:37

St. Thomas Aquinas shows "Quod anima sit tota in toto et tota in qualibet parte" ("that the whole soul is in the whole body and in each of its parts") in Summa contra Gentiles lib. 2 cap. 72. He shows that the soul is

  • in the whole body (ibid. ¶2),
  • "the form of the whole body in such fashion as to be also the form of each part" (ibid. ¶3), and
  • wholly in each part of the body (ibid. ¶4), despite the parts having such diverse characters (ibid. ¶5)
  • So why doesn't organ transplantation split the soul? – viuser Oct 23 '17 at 21:40
  • @wolf-revo-cats Because the soul is indivisible; it is not a body: – Geremia Oct 24 '17 at 23:09
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    @wolf-revo-cats «[4] Then, too, every body is divisible. Now, whatever is divisible requires something to keep together and unite its parts, so that, if the soul is a body, it will have something else to preserve its integrity, and this yet more will be the soul; for we observe that, when the soul departs, the body disintegrates. And if this integrating principle again be divisible, we must at last either arrive at something indivisible and incorruptible, which will be the soul, or go on to infinity; which is impossible. Therefore, the soul is not a body. » – Geremia Oct 24 '17 at 23:09

"How can this still be reconciled with the supposed existence of a cohering form of the body which can be identified with “soul”?"

This is the Aubrey de Grey question. For Aristotle the issue was that if you cut off an arm it stops moving like an arm. Or, if you kill a red pine, it doesn't move in the same way. Dead wood has a different nature. What it does, if not influenced externally, changes. The soul means about the same thing as being alive. The difficulty comes in when we want to say someone "isn't there", you know? Or, that one is not themselves. That could happen even without dying, a grand transformation of temperament.

On the other hand, obviously, you signal the problem of whether change in the flesh, like the ship of Theseus, amounts to essential change. The way Aristotle would approach that is empirically. One must look at such cases, and discuss them with serious-minded persons. And thereby come to a conclusion. Aristotle was not a dogmatist in the crude sense the word has taken on of late years.

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