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A Brief History of Christian Conceptions of the 'Soul'

It is sometimes said that Christianity presupposes the existence of a soul, that, due to the progress of science, this view is no longer credible, and that, therefore, Christianity can no longer be taken seriously. It is very probable that there are some combinations of views, widely held among self-identified 'Christians', which can be effectively criticized along these lines. However, there are several puzzling features about this line of thought. The first is that it is not clear what the relevant 'progress of science' is supposed to be. Neuroscience is indeed advancing, but it can hardly be considered so advanced already, today as to have shown that all mental phenomena are explicable in purely physical terms. Maybe we have some reason for believing that mental phenomena will one day be explained in purely physical terms, on the basis of the 'track record' of science or something, but this sort of argument is surely not strong enough to be a reason not to take the contrary view seriously.

More interesting, in my view, are the problems physics makes for the proponent of non-physical souls. These include issues about conservation laws and Maxwell's Demon, among others.

In the end, however, I do not think the 'progress of science' has made any problems for non-physical souls more serious than the original problem: mind-body interaction. Of course, that problem is hard to beat: it's a pretty devastating objection. The theory simply doesn't answer one of the most important questions it's supposed to answer. I don't think the progress of science is likely to find problems more serious than that one.

So that's the first issue: the line about the 'progress of science' is more or less irrelevant, and could be cut out. But that doesn't de-fang the line of argument at all (in fact it might make the argument stronger). It doesn't particularly matter why belief in non-physical souls is not credible. If it's really true that that belief is not credible, and it's really true that Christianity requires that belief, then Christianity itself is not credible as a belief system.

Let's get more specific. The view I've been calling 'belief in a soul' should be called, more precisely, Cartesian dualism. This is the view that, for every human being there are two distinct 'things' (substances) - a physical thing (substance), called the body, and a non-physical thing (substance) called the soul. The person (you or me) is a composite, a unity, of the body and the soul, but body and soul are fundamentally separate, independent things (which is what is meant by calling them 'substances'). According to many Cartesian dualists (including, I imagine, all or nearly all of the Christian ones), your body and soul will in fact exist separately, after your death. I once heard a Christian philosopher (I don't remember who) who supported this view compare death to amputation. Dying, on this view, is like having your arm amputated, only it's even worse: your whole body is amputated! (The philosopher in question called it a 'corpusectomy'.) As long as your body and soul are united, both are parts of you, but if they become separated (as they do in death), you will continue to exist, having your soul as your only part.

Now, this is not the only thing that 'belief in a soul' could mean, but it's what non-philosophers (and sometimes philosophers as well) nowadays ordinarily mean by that phrase. Not all of the views that could possibly be described as 'belief in a soul' face the problems I've mentioned, but Cartesian dualism does face them, so that, combined with how widespread the view is, is a reason for thinking that that is what is meant in the line of argument we started with.

So, is Cartesian dualism really the Christian position on the nature of human persons? If Cartesian dualism is really not a tenable theory, is Christianity thereby rendered untenable?

Well, for starters, I have no doubt that the vast majority of Christians today are Cartesian dualists. If you ask them why, they will probably tell you that they believe in souls because the Bible talks about souls all the time. It is true, of course, that the word 'soul' appears with great frequency in every English translation of the New Testament I know of. It is further true that, in contemporary 'plain English,' talk about 'souls' basically implies belief in Cartesian dualism (not only that: it basically implies belief in an afterlife with reward and punishment for souls!). However, it is a well-known (to scholars) fact that the Greek word psuche which is traditionally translated 'soul' has no such implication. The Epicurean philosophers of ancient Greece and Rome, who notoriously believed in nothing - absolutely nothing at all - besides 'atoms in the void,' did not go around saying they didn't believe in souls (psuchai). Rather, they went around saying that souls were made out of atoms! This was a lively, ongoing debate at the time the New Testament was written. So the mere use of the word psuche means basically nothing here. The word could perhaps be better translated 'self.' (Note that in the Gospel of John, psuche is usually translated 'life.')

"Ok," you say, "but Christians all agree in interpreting this talk in Cartesian dualist fashion." No, they don't. For instance, Christian philosopher Peter van Inwagen and theologian John Polkinghorne both believe that the human mind or self is purely physical. Other Christians, like philosophers Nancy Murphy and Trenton Merricks, believe in a view called property dualism, which says that a human person is just one substance, with two kinds of properties (features), mental and physical. According to this view, although the mental and the physical are fundamentally different, you can't separate out a 'mental part' and a 'physical part' of a human person. Of course, insofar as property dualism is still a dualism - it takes the mental and the physical to be fundamentally different from one another - it faces many of the same difficulties as Cartesian dualism. The point, however, is that Cartesian dualism is not universal among Christian thinkers.

"Ok," you say, "but surely Cartesian dualism is the orthodox, or conservative, or traditional Christian view. I mean, after all, if you pick just about any view you want, you can find some person somewhere who is supposed to be a Christian who believes it. There are people out there [I (Kenny) have personally met some] who identify as Christians who don't believe there was ever such a historical person as Jesus of Nazareth. But the Christian view of things is that there was such a person, that he was the Son of God, and that he rose from the dead. Just because some people who are call themselves 'Christians' don't believe something doesn't mean it's not the Christian view."

Now, this is where things get interesting for me. You see, I'm a specialist in the history of early modern philosophy, and 'Cartesian dualism' is, of course, named for the early modern philosopher Rene Descartes. It is quite interesting to me that nowadays Cartesian dualism is widely thought to be the orthodox, conservative, or traditional view, because, when Descartes and his followers advocated it in the 17th century, it was widely regarded as radical, revisionary, and heterodox. That is, in the seventeenth century, many Christian leaders, both Catholic and Protestant, regarded Cartesian dualism as borderline heretical, and perhaps as having consequences that were actually heretical. So now that I've already written this large quantity of text, I'm going to actually do what I said in the title of this post, and give a brief history of Christian conceptions of the soul (brief for a history of this topic; not very brief for a blog post!), aiming to explain why Descartes's theory was originally regarded as of questionable orthodoxy and is now widely regarded as the standard of orthodoxy.

This story begins the same way as most stories about the western intellectual tradition: in the beginning, there was Plato. The fundamental distinction in Plato's philosophy is the distinction between 'sensible' things (i.e. those that can be detected by the five senses) and 'insensible' or 'intelligible' things (those that can only by understood with the intellect). For Plato, the sensible realm is a realm of illusion from which we struggle to break free. The sensibles are corruptible and corrupting; they are impure; they are unreliable, and in a constant state of flux. Intelligible things are stable, pure, and good. You and I, according to Plato, are intelligible things. We are non-physical souls trapped in physical bodies, and we need to get out.

Now, in many ways early Christianity was closely aligned with Platonism. The talk about the 'Word' (logos) at the beginning of John's Gospel has Platonic overtones, and Paul's spirit, soul, flesh trichotomy looks like Plato's distinction between what he calls the wisdom-loving, glory-loving, and money-loving parts of the soul. There's also a little bit of interesting Platonic jargon in the Epistle to the Hebrews. It has been a matter of dispute for basically the entire history of Christianity whether, and to what degree, the New Testament writers were influenced by Greek philosophy, but for anyone familiar with Greek philosophy - then or now - the parallels seem obvious. That's not to say it couldn't possibly be coincidence; it's just that if you've been reading Plato, it's pretty natural for you to then see his views in the New Testament. Thus many early Christians, most notably St. Augustine, adopted broadly Platonist views, including belief in a purely non-physical soul.

There was, however, a problem. For Plato, the physical world is inherently deceptive and impure, and many of his followers regarded everything physical as downright evil. This is the essence of the Gnostic heresy against which the leaders of the early Church, beginning with the apostles themselves, fought. According to Genesis, the physical world was created by God and declared to be good. According to Revelation, there will someday be a 'new heavens and a new earth.' That is, the ultimate paradise which God intends for the elect is a physical paradise, and St. Paul assures us that, in it, we will have bodies (1 Cor. 15:35-44). St. Paul also says that "we [Christians] ... groan within ourselves, eagerly waiting for adoption, the redemption of our bodies" (Romans 8:23). The Apostles' Creed likewise affirms "the resurrection of the body."

The Gnostic heresy, in its most extreme form, actually asserted that the physical world was created by an evil lesser god, known as the 'demiurge', and not by the true God, the Father of Jesus. The Christian Church emphatically rejected this view, insisting that the physical world was originally good, though corrupted by sin, and insisting that the afterlife would be physical. This implies a rejection of Plato's view that having a body is a bad thing for a human being.

Although some Christians (again, including Augustine) tried to develop basically Platonist views which didn't have the objectionable anti-physical tendency, the association of Platonism with the Gnostic heresy made it natural for Christians to turn to the main competitor of Plato's view, which was, naturally enough, Aristotle's. Aristotle's view united body and soul in a much stronger way than Plato's, and made it clear that a human person was a single, unified, substance made up of body and soul. (Plato, recall, says that the person just is the soul, and this is what makes possible his view that we are trapped in our bodies, and that this is bad.) Aristotle's view is a little complicated, and is much farther removed from views we are familiar with nowadays, so you'll have to bear with me on a digression about some general principles of Aristotelian philosophy.

According to Aristotle, everything in the world has two components, which he calls matter and form. The matter is the stuff of which the thing is made, and the form is the organizing principle responsible for the shape and behavior of the thing. Forms arrange matter toward goals. The forms of living things arrange their matter in order to accomplish growth and reproduction.

Because the form is responsible for organizing the matter towards ends, the form is an active principle. That is, it's in virtue of the form that an object can act (push other things around, and what not). The matter is a passive principle. It is in virtue of the matter than an object can be acted upon (get pushed around, etc.).

I said that, for Aristotle, everything is made of both form and matter, but there is an exception: God. God, according to Aristotle, only acts and is never acted upon. That is, it's impossible for anyone or anything to do something to God (he can't be pushed around or bashed on the head or anything). So God, and God alone, is a form without matter. With this one exception, Aristotle holds that it is impossible for there to be matter without form or form without matter. Matter has to be in some arrangement and behave some way or other, and a form has to have some matter to organize.

Now, according to Aristotle, the soul is the form of the human being, and the body is the matter. The soul is the thing that organizes the body into a living being that eats and grows and reproduces, and also walks and talks and pursues its goals. That, for Aristotle is what the soul is: it's an organizing principle, and it can't exist without having something to organize.

There are some similarities between the Aristotelian view and contemporary functionalism, currently the most popular view among those philosophers who think that human persons are purely physical. This view is often summarized by the slogan, 'the mind is the software of the brain.' So this view also links the mind to a particular functional organization of the body (specifically the brain). However, we should not exaggerate the similarities: for the functionalists, the mind is a particular functional organization of the body, whereas for Aristotle the soul is an organizing principle, that is, the soul is a real thing distinct from the body which makes the body have the functional organization it has.

Now back to our history. As I said, Aristotelianism was the main competitor to Platonism in the ancient Greco-Roman world. Since Platonism was associated with Gnosticism, it was natural for Christians to begin to turn toward Aristotelianism, and that's exactly what happened. Aristotelianism makes the person a unity of mind and body, and shows why it is that human persons ought to have - indeed need to have - bodies. It makes the body a good thing for the soul, by making the soul depend on the body (and the body on the soul). By the fall of the Western Roman Empire, and throughout the Byzantine/Medieval period, Aristotelianism was probably the majority view among orthodox Christian theologians (though, again, Augustine is an important exception).

But there were a few special problems facing Christian Aristotelians. First, angels were thought to be disembodied souls. Second, it was thought that human souls existed in a disembodied state in between their death and the end of the world.

One solution, given by St. John of Damascus in his Concise Exposition of the Orthodoxy Faith (8th century AD), is to deny that angels and disembodied humans are really purely non-physical. St. John argues, essentially, that if they truly had no bodies at all - no matter - they would be pure actuality, that is, they would be God. So he holds that angels and disembodied humans have bodies, but their bodies are too 'subtle' and 'rarefied' to be detected by our senses. We thus call them 'immaterial' or 'incorporeal' or 'disembodied' in a relative sense.

The contrary line is taken by St. Thomas Aquinas (13th century AD). Aquinas argues that angels are really truly non-physical, having no matter at all, but says that their nature is beyond our ability to understand. Now, Aquinas thinks that, somehow or other, the angelic souls can be acted upon without matter, and can act, although it is not by organizing matter that they act. And so he says essentially the same thing about human souls when separated from their bodies. Fundamentally, for Aquinas, the soul is a form; its nature is to organize a body. Aquinas thinks that forms in general continue to exist when the bodies they organize are destroyed, and they can come to organize another body later. But how a soul could function - act or be acted upon - in any way when it is not organizing a body is a deep puzzle for Aquinas, because the soul's function just is to organize the body. Furthermore, forms in general cannot be acted upon; the substance that has the form can be acted upon in virtue of its matter. Yet Aquinas needs to hold that disembodied souls are acted upon.

Now we get to Descartes. The fundamental opposition in Cartesian philosophy, analogous to Plato's opposition between the sensible and the insensible, is between body and mind. The nature of body is to be extended (take up space) and the nature of mind is to think. In the Sixth Meditation Descartes is careful to avoid falling into Gnosticism. He insists that the mind is intimately united to the body, and that the person is a unity of mind and body. (The view that Platonic and Cartesian dualism are fundamentally the same is a popular misconception: from the perspective of Christian theology it is critically important that, for Descartes, the human person is a unity of mind and body, whereas for Plato the human person is a mind trapped in a body.) However, Descartes is completely unable to give any account of this union. For Descartes, the nature of mind and the nature of body are radically different and in no way related. This contrasts with the Aristotelian view in which the nature of matter is to be able to be organized in a variety of ways, and the nature of mind (form) is to organize some matter.

Where did Descartes's view come from? Well, we know from his letters to Mersenne, his publisher, that Descartes started writing the Meditations after he heard about the condemnation of Galileo, in an effort to sell Galilean science to the Catholic Church. In Galilean science (as in today's science) there is no role for real organizing principles (Aristotle's 'forms'). 'Organization' is no more than some bits of matter being located here and others being located there, and what functions an organization does or doesn't perform depends on how the bits of matter bump into each other. This sounded an awful lot like Epicureanism, and some philosophers, like Hobbes and Gassendi, were indeed bringing back the Epicurean picture according to which everything, even the soul (perhaps even God?), was just 'atoms in the void.' The Catholic Church wasn't going to accept this, so Descartes tried to get the soul, which had so many religious ideas tied up with it, safely away from physics, so that physics could proceed unmolested by theology. (Read that again. Descartes' goal was to prevent theology from impinging on physics. Today a lot of people endorse dualism to keep natural science from impinging on their theology, or their views about human freedom, or whatever, just the reverse of Descartes.) The trouble is, if you get the soul too far away from physics then it's hard to see how the soul and the body could interact at all, let alone how the two of them could form a unity of any sort. This objection was effectively pressed against Descartes by Princess Elizabeth of Bohemia, and Descartes was eventually forced to admit that he had no answer.

Of course, he tried all sorts of things. Descartes believed that conservation of momentum was a fundamental law of physics, but he didn't have vectors, so he thought that changes in direction wouldn't violate the law. So for a while Descartes thought the soul acted on the body by changing the direction of particles in the brain. (No word on how the body acts on the soul.) This is similar to the view of the ancient Epicureans that free will comes about because atoms sometimes randomly swerve out of their path. It's also similar to the later view of those who think free will works by the mind controlling wavefunction collapses in the brain. I hope it doesn't need saying that none of these views is even a little bit plausible.

Descartes's followers gave up. The largest contingent of them, including most famously Nicolas Malebranche, held a view called occasionalism according to which (I kid you not) God notices that I am will my arm to move, so he moves it for me, and God notices that my arm is being pricked by a pin so he makes my soul feel pain.

Leibniz took another approach. According to Leibniz, there is no interaction between soul and body at all. God simply designed the soul to behave according to certain laws, and the body according to others, and made sure that the laws were such that the body and the soul were always synchronized. The intimate union, according to Leibniz, consists, basically, in the fact that the soul is much more aware of the condition of its body than of anything else in the universe. (This is a simplification.)

All of these 'modern' views were attacked by theological conservatives, especially among the Jesuits, as basically leading back into Gnosticism. The human person becomes a soul who just happens, accidentally, to be joined to a body at present. There is no unity of soul and body. Leibniz (who, as a Lutheran, didn't have to worry too much about making the Jesuits happy) corresponded with several Jesuits and spent a good deal of time trying to develop a theory that would involve an adequate degree of unity between soul and body. His mature theory, while still involving 'pre-established harmony,' as he called it, brings in some Aristotelian machinery to try to do the job.

In the 17th century, these 'modern' philosophers, who accepted Cartesian dualism or similar views, were considered revisionists, and dangerous to traditional religion. What happened between then and now to reverse the verdict?

What happened is we got some different heretics. Recall that the Aristotelian view did such a good job making the soul and body into a unity that it had trouble explaining how a soul could exist and function in a disembodied state, which was supposed to be the case for angels and also for humans between death and resurrection. Well, in the 17th century there started to be a louder voice coming from some Anabaptists and Socinians in favor of what is sometimes called the 'soul sleep' hypothesis, according to which the soul cannot function without the body. In some versions, the soul doesn't exist until God reconstitutes the body at the resurrection; in other versions, the soul exists but is unconscious. Now I myself am not convinced that this contradicts anything essential to Christianity. Indeed, I think this view is held by all four of the present-day Christian thinkers I mentioned as non-Cartesians about souls. But this view is contrary to Roman Catholic, Lutheran, and Calvinist doctrine, and it seemed to be supported by the Aristotelian view of the soul. More extreme than this, throughout the 18th and 19th centuries, it became more and more common for people to deny that there was any afterlife at all. Now Cartesian dualism nicely answers these objections for, on Cartesian dualism, the existence and functioning of the soul is totally independent of the body, so there is no reason at all why the dissolution of the body should destroy the soul or even stop it from functioning. Of course, this is also precisely the source of Cartesian dualism's biggest problems.

Ok, back to the present. Suppose a Christian denies that there is a non-physical component to a person, perhaps endorsing a form of functionalism. We noted that this has some similarities to the Aristotelian view. It also seems to be in the same position as the Aristotelian view with respect to Christian doctrine: against the Gnostics, the functionalist holds that a human person is genuinely physical, and that this is not a bad thing for humans, since humans can't exist without their mental functions being instantiated by a system of some sort or other. But the functionalist has trouble figuring out what to say about the afterlife. Note, however, that the functionalist might not have that much trouble with this, since one of the points of functionalism is to hold that if the same functional organization was implemented in some other system you'd have the same mental states. (Note that this is another place where functionalism is similar to Aristotelianism: the same form could organize different matter.) Many functionalists further hold that it is possible for a person to be transferred from one system to another (uploaded to a computer, for instance). (Others hold that the person in the computer would be a copy of the original person, rather than actually being the same person.) So if your functional organization was re-implemented in some other system somewhere in this or another universe, then you would survive, although the physical system here on earth which implemented you was destroyed.

Cartesian dualism, on the other hand, gets the after-life almost 'for free,' but it's utterly baffling how the soul could be in any way united to the body. This is, of course, a serious problem for the inherent plausibility of Cartesianism, but it is also a theological problem; it's a tendency toward Gnosticism. I would go so far as to say that the theological problem for Cartesianism is more serious than the theological problem for functionalism, and I think I have the majority of the first 17 centuries of the Christian Church behind me on that. Of course, the inherent seriousness of the problem is less important than whether the problem is solvable. That's a question I won't enter into here.

My concern here has been to examine, from a historical perspective, the question of what Christianity, qua Christianity, commits one to regarding human persons and their 'souls'. My conclusion is that Christianity commits one to the claims (1) that the human person is a unity of mind and body, and (2) that the human person continues to exist after physical death. Insofar as there is an objection to Christianity (rather than to some theory of the mind held by some particular Christian) here, the objection is that it's hard to hold these two things together. But it's far from clear that it's impossible to hold them together. It's also simply not true that trying to hold these two claims together commits one to Cartesian dualism: after all, Cartesian dualism appears superficially to be inconsistent with claim (1).

As far as the history goes, it seems that which view of mind is regarded as the 'safe,' 'conservative,' 'traditional' Christian view depends on which of the two principles is most under attack at the moment. That makes psychological sense. But of course the truth of the matter can't possibly depend on that sort of thing, so we should resist the urge to run to Cartesian dualism just because the doctrine of an afterlife is under attack. Cartesian dualism's got serious problems, and some of them are theological. (Others, as I noted at the beginning, are scientific.) In the end, we have to say: philosophy of mind is hard, and Christianity might put some constraints on our theorizing about the mind, but it certainly doesn't give us the answers. In the present context, that's good news, because it means that whatever problems there are for Cartesian dualism are not, as such, problems for Christianity.