What Is a Soul and What Does It Do?

Soul this and soul that. The idea of a soul permeates popular culture, from soul music, to feeling things in your soul, to having soul, to this and, indeed, that. Theologically, souls are a really important part of many theists’ theological frameworks.

But what is a soul? And what do they do?

The answers to these questions are harder to nail down than you might think for something so commonly invoked.

Catholic doctrine states it is:

…the innermost aspect of humans, that which is of greatest value in them, that by which they are in God’s image described as ‘soul’ signifies the spiritual principle in man.

That seems a bit nebulous. Let’s go to a fairly well respected (by Catholics, at any rate) theological source: The Catholic Encyclopedia. And in all honesty, the opening section really says it all:

The question of the reality of the soul and its distinction from the body is among the most important problems of philosophy, for with it is bound up the doctrine of a future life. Various theories as to the nature of the soul have claimed to be reconcilable with the tenet of immortality, but it is a sure instinct that leads us to suspect every attack on the substantiality or spirituality of the soul as an assault on the belief in existence after death.

That is to say, we’re not really sure what it is, but we really need it to believe in immortality, and thus heaven and hell. Therefore, the soul is pretty darned important, but also pretty darned mysterious or incoherent.

Building on previous thought, St Thomas Aquinas thought as follows:

  • the rational soul, which is one with the sensitive and vegetative principle, is the form of the body. This was defined as of faith by the Council of Vienne of 1311;
  • the soul is a substance, but an incomplete substance, i.e. it has a natural aptitude and exigency for existence in the body, in conjunction with which it makes up the substantial unity of human nature;
  • though connaturally related to the body, it is itself absolutely simple, i.e. of an unextended and spiritualnature. It is not wholly immersed in matter, its higher operations being intrinsically independent of the organism;
  • the rational soul is produced by special creation at the moment when the organism is sufficiently developed to receive it. In the first stage of embryonic development, the vital principle has merely vegetative powers; then a sensitive soul comes into being, educed from the evolving potencies of the organism — later yet, this is replaced by the perfect rational soul, which is essentially immaterial and so postulates a special creative act. Many modern theologians have abandoned this last point of St. Thomas’s teaching, and maintain that a fully rational soul is infused into the embryo at the first moment of its existence.

What are important takeaways here are that it is rational and that it is substantially separated from the body, though related and deriving properties from it. These ideas aren’t made easy by various authors within the Bible using the term, or a given term to mean the soul, rather ambiguously (at times meaning the whole body or person, e.g Ezekiel).

Descartes famously concluded that the soul was connected to the pineal gland:

Descartes conceived the soul as essentially thinking (i.e. conscious) substance, and body as essentially extended substance. The two are thus simply disparate realities, with no vital connection between them. This is significantly marked by his theory of the soul’s location in the body. Unlike the Scholastics he confines it to a single point — the pineal gland — from which it is supposed to control the various organs and muscles through the medium of the “animal spirits”, a kind of fluid circulating through the body. Thus, to say the least, the soul’s biologicalfunctions are made very remote and indirect, and were in fact later on reduced almost to a nullity: the lower lifewas violently severed from the higher, and regarded as a simple mechanism. In the Cartesian theory animals are mere automata. It is only by the Divine assistance that action between soul and body is possible.

The Catholic Encyclopedia confusingly concludes, however:

As regards monistic systems generally, it belongs rather to cosmology to discuss them. We take our stand on the consciousness of individual personality, which consciousness is a distinct deliverance of our very highest faculties, growing more and more explicit with the strengthening of our moral and intellectual being. This consciousness is emphatic, as against the figments of a fallaciously abstract reason, in asserting the self-subsistence (and at the same time the finitude) of our being, i.e. it declares that we are independent inasmuch as we are truly persons or selves, not mere attributes or adjectives, while at the same time, by exhibiting our manifold limitations, it directs us to a higher Cause on which our being depends.

Such is the Catholic doctrine on the nature, unity, substantiality, spirituality, and origin of the soul. It is the only system consistent with Christianfaith, and, we may add, morals, for both Materialism and Monism logically cut away the foundations of these. The foregoing historical sketch will have served also to show another advantage it possesses — namely, that it is by far the most comprehensive, and at the same time discriminating, synthesis of whatever is best in rival systems. It recognizes the physical conditions of the soul’s activity with the Materialist, and its spiritual aspect with the Idealist, while with the Monist it insists on the vital unity of humanlife. It enshrines the principles of ancient speculation, and is ready to receive and assimilate the fruits of modern research.

This is wholly unsatisfying. Indeed, reading the entry, one comes away thinking it is just a ruse to confuse the reader so much that they forget why they were coming to read the piece in the first place. There is no real, easily discernible definition of what a soul is or does, merely lots of discussion of the idea of it over history.

Perhaps Richard Swinburne can help (The Evolution of the Soul):

It is a frequent criticism of substance dualism that dualists cannot say what souls are. Souls are immaterial subjects of mental properties. They have sensations and thoughts, desires and beliefs, and perform intentional actions. Souls are essential parts of human beings.

The problem with any claims about the soul is that they end up being theological assertions: mere assertions. Because, if we could evidence what souls were, we would know what souls were. It is pretty obvious. So a soul ends up becoming something that is unevidenced, and this is why there is disagreement (amongst Christians, for example) over what they really are.


Souls as Rational

If souls are to be rational, what really differentiates them from consciousness? Though we don’t fully understand consciousness, we know it supervenes on the brain. Without the brain, we are not conscious. Moreover, if you take drugs or stick a fork into your eye socket and into your brain, are tired, hungry or any number of physical and easily evidenced things, your consciousness will be affected.

In order to be rational, and yet be separate to the brain and consciousness, I am not sure what the soul can be. If it is consciousness, then it is…consciousness, and it will die with your brain death.

If it is rational, then what part does it play in your life throughout your living years, if separate from your consciousness? What does it do that your consciousness does not? If we are judged either at death or contemporaneously for the decisions our conscious brain takes, then what is the soul in this context? What responsibility or part in those actions does it have or play? Is it just a carbon copy or reflection of the consciousness that can continue after brain death? It would have to be invisibly connected to the body, then, in some mysterious way.

We understand the parts of the brain involved in rational processes, and so making such claims about the soul is to special plead this can happen without the physical matter of the brain.


A real problem for the soul is the very thing it is supposed to function for: death. When we die, it is generally assumed by theists that the soul is the immortal (or annihilated) entity that continues our existence into whatever realm we are deemed justified in inhabiting. If we go to heaven, however, if the soul looks like consciousness, then what part of our life is the soul supposed to represent?

Imagine I am an eighty-year-old person who has severe dementia and I go to heaven. Do I take that dementia with me as that was “me” at death? Or do we get some kind of cherry picking of representation throughout my life? Is it “me” five years before death, ten, or at what point?

Is the soul, then, so far connected to my conscious self (and thus my memories and sense of self), in order to get around this problem, that it ends up being essentially unrelated to “me” – the entity being judged in the first place?

These are fundamental and rather terminal problems for the soul (I set many of these out in my book The Little Book of Unholy Questions).


If the soul is rational, but not connected to or reflective of lived consciousness, then in what state is the soul representing me in heaven? How is it, therefore, rational in any way reflective of my everyday conscious rationality?

Either the soul is our consciousness at death (a copy or reflection), and therefore, I live out eternity in that state (in dementia or whatever mental state at death I have), or it has no connection to our consciousness (at death), in which case it has no substantive connection to me, who I feel I am, and how I operate in the mental realm!

Perhaps God just chooses the best version of me, and that’s the “me” that gets into heaven to live out for eternity. But that is riddled with issues.

Ensoulment and IVF

The other end of the human timeline is equally fraught with problems. When do humans become ensouled? If it is at conception, then there are some pretty big hurdles for the soul thesis. For example, certain twin embryos don’t develop until some time after conception, so this model can’t work, or must be radically altered ad hoc.

Another hurdle is IVF. Fertilised embryos, arguably ensouled with supposedly rational properties and identity, are frozen, in theory infinitely. What happens to this rational entity as the embryo – that early human physical form – is frozen indefinitely? Is there some soul bar in the netherworld where they hang out until they are summoned back?

It’s interesting to wonder how a one day-old embryo can have any rational properties (or the soul). If the soul has rational properties at this stage, then that rationalism has nothing to do with the developed rationalism (dependent on the brain and life of the later individual) that is created over time by that (what eventually becomes a) person.


The soul is incoherent as an idea, and yet pervades in theological thought. It is an assertion, and one that doesn’t work. Go figure.

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