Catholic Medical Quarterly Volume 70(3) August 2020

Descartes’ error on the nature of the Human Soul

Dr Adrian Treloar, MRCPsych, FRCP, MRCGP



Lessons from and implications for the care of people with dementia, learning disability, and care of the unborn. Plus a reflection on Transgender issues.



 The Cartesian view of “I think, therefore I am”.

The fame of Descartes is summarised in a single sentence. “I think, therefore I am”. In one sense that statement is self-evidently true. We can know we exist only because we are aware that we exist and being aware of our existence requires us to think about that existence. It follows that we can prove that we exist because we are thinking beings who seek to understand our existence. It may well be that Descartes’ popularity is, in part at least, predicated upon the simple truth and logic of that sentence.

But not many people realise the impact Descartes has had on our ideas of the human soul. ‘Cartesian dualism’ is the view that the human soul is, in essence, our mind and the way we think. Descartes saw the body as being separate from the mind or intellect which leaves the body behind when we die. Radically separating mind and body leads, as I shall seek to show, to some serious (and genuinely tyrannical) conclusions in our society today, even if perhaps not many hold the exact position Descartes himself did.

Unlike Descartes, Aristotle thought that the human intellect was one among various powers of the soul. Humans could demonstrate that power when we think for ourselves. Aristotle clearly saw intellect as a part of the human soul. But he also thought that the intellect was not the whole of our soul [1].

St Thomas Aquinas, like Aristotle before him, held that the human soul was naturally related to the body as its life-principle. He also held that it was immaterial in character and that it survived the body so that it could be reunited with the body by the Resurrection. In life, the body and soul are intimately connected. A simple practical demonstration of this is given by Eckhart Tolle [2]. He noted that if we stop physically, we become more aware of thinking. While our mind is distinct from our body, it is still, in life, intimately connected. Thus, as St Thomas concluded, the soul incorporates the mind or intellect but is also greater than the mind.

It was in that context that Descartes produced a dramatically different view of the human being. Descartes - at least as most people understand him [1]- rejected the Aristotelian view that human beings, like other living things, possess a ‘life principle’. He thought that living things are complex pieces of machinery designed and created by God. Mechanical processes accounted for growth and some behaviours, but those mechanics could not (he believed) account for human thought. As Jones[1] puts it, “thus he combined a mechanical view of the universe with a radically subjective view of the self ”. Cartesian dualism therefore sets out a view that the body and soul are separate. Although some experiences may arise from the mind-plus-body combination, Descartes suggests that the mind exists in the body but is separate from the body. After death the body is left behind (and indeed buried 2 metres underground in a box) while it is the mind that goes forth towards the Gates of St Peter.

Descartes’ heritage

It does, nowadays, seem to be the prevailing view that our mind is the bit of us that we can imagine getting to Heaven while our body is a machine which eventually will break and stop working altogether - at which point it is permanently discarded. In the Twentieth Century Ryle summed it up when he said that Descartes had portrayed the mind as ‘a ghost inside a machine’ [3].

Degrees of personhood

From “I think, therefore I am” springs rapidly a conclusion that “I am what I think”. Or even, as a good priest friend commented to me while I was developing these thoughts, “I am what I produce”. If my existence relies upon the fact that I think, then it is easy to conclude that the more I think, the more of a ‘person’ I am. Or to put it another way, those who are more intelligent, high achiev­ing etc. are more of a ‘person’ than others. For example, a Nobel prize-winner may well be more of a ‘person’ than a young child or an adult of low IQ. Put even more crudely the President of the United states may well, (in a logical continuation of Descartes dualistic view that the mind is the soul) be more human than unskilled workers (upon whom we rely every day). While such a view is clearly deeply objectionable, anathema and very dangerous, some version of it is, if we are honest, a strong current in modern thinking.

It might be argued that it is not fair to blame Descartes for the successors whom he unwittingly influenced and who have drawn such conclusions. But perhaps, it is fair to suggest that Descartes radical separation of mind from body, did indeed make the path clear for such conclusions.

Misuse of the concept of personhood

Modern concepts of 'personhood' have been used to claim that the embryo is not a person with the rights of a person because it does not yet think. The claim that embryos are not yet properly human because they cannot yet feel or think as we do appears to be widespread. That view of the humanity (or lack thereof) of the unborn is in turn used to underpin arguments that it is not wrong to abort babies with disabilities.

There is a common view that people’s humanity is steadily and then totally removed by a progressive dementia. Descriptions of dementia as a living death [4] predicate themselves on the observation that dementia “Savagely and pitilessly, ... strips away memory, language and personality, leaving only the shell of its victims behind”. Many people accept that, as well as diminishing intellect and ability, the illness does indeed erode our humanity and personhood.

People with a learning disability too, may be perceived to have less personhood as they cannot express themselves as easily or as well as others. Although we must state that view is desperately untrue.
And yet we often see the most acute and beautiful humanity in in people with severe disability. The book ‘The Diving Bell and the Butterfly” stands out as an exemplar of that [5].

In the last century, such views of humanity and the supposed lack of full moral rights of people with learning disability and those of certain races etc led to some of the greatest atrocities ever seen. Modern concepts of personhood are very much focused on the ethics of abortion and euthanasia. Many ethicists would now deny the rights of personhood to those who cannot understand, cannot feel pain or who have profound intellec­tual disability. And the absence of personhood is used as a justification for abortion, euthanasia and experimenting on human embryos.

In connecting the soul so closely with the intellect, Descartes (unwittingly I suspect) gave strong support to the modern view that person-hood requires the ability to think. From that it follows that human embryos can be experimented upon and then discarded, while people with severe dementia or people who are in a persistent vegetative state are not truly people (and may in any case be better off dead).

Lessons from real life

My younger brother died at the age of 20 and was profoundly intellectually disabled. Despite that, or perhaps even because of that, he had a humanity that is so often clearly seen among people with Down’s Syndrome. His humanity fully transcended his inability to speak, or his inability to understand blindness when it happened at the age of 19. He was a loveable, delightful (and somewhat cheeky) chap. Fully human but profoundly disabled. And he had about 300 people at his funeral. People wept when he died. His humanity shone brightly through his disability and was a dimension of him that incorporated his whole being and certainly not just his intellect. And I have seen that demonstra­tion of humanity so many times in other learning-disabled people. My brother is but one example.

In my work as a consultant psychiatrist for the elderly, people with profound dementia have con­tinued to express a deep and true humanity which is, again, not prevented by their loss of intellect. Perhaps even, in their vulnerability and depend­ence upon others, their dignity and their humanity is even more tenderly expressed and highlighted. With good care, our humanity is acknowledged as transcending our intellectual loss.

While I was writing this paper I found that many people agreed with the view that, in our vulnerability and our dependence upon others, our humanity is emphasised, and perhaps even enhanced. For a person to be severely unwell and to have a severe dementia may even (in some cases) increase our ability to see that person’s humanity. So often, while caring for people with very advanced dementia, I have seen that human­ity brightly displayed. The view that the loss of intellect in people with dementia equates to a loss of humanity is clearly at variance with so many people’s experience of dementia. Descartes' descendants, if they use the word soul at all, connect the soul very much with the intellect. But seen through the lens of dementia care, that view is, simply, wrong.

In the unborn and newborn too, attempts to circumscribe the right not to be killed have been based upon a requirement that the child have the ability to think or at very least, to feel pain, or to respond to other stimuli. Such requirements (which in essence deny the personhood of some children, born or unborn) stem ultimately from the Cartesian stress on the primacy of rational thought.

“I think, therefore I am”, however true, has led some to deny the personhood of the embryo and the foetus. “I am, therefore I am” would set out the right of the unborn far better. St Theresa of Calcutta famously picked up destitute and dying babies from the gutters of Calcutta and simply held them aloft and showed their dignity and worth. She loved them because they were, not for what intellect they had or what they might one day produce.

My experience with the disabled, the learning disabled, and people with dementia and my experience of the unborn has forced me to reject Cartesian dualism. “I think, therefore I am” does not describe what I see. Thinking may be a sign of our humanity, our moral personhood, but it is not the only sign. “I am, therefore I am” would seem a more adequate description of what I see.

The descendants of Descartes are denying the humanity of those who are disabled, frail and dying. We need to challenge this view. The human soul is far greater than the human intellect.

The tyranny of “I am what I think”.

The world concludes that if your intellect is reduced or not yet developed, then morally you are less human, or you are not human. The unborn and the disabled may be killed, including for eugenic reasons to improve the human gene pool. All that is required is that these people be unable to pass the thinking test.

Tony Bland was described having no best interests[1]. Alfie Evans' best interests were described as being dead[2]. Therefore, he was barred from treatment abroad as survival could not be in his best interests[3]. The ability to deny the humanity of a person simply because he cannot feel pain or has no obvious intellectual functioning becomes tyrannical. The disabled and unwell (as well as their families) come to fear the authorities who may conclude “you do not think, therefore you are not” or worse still, “you do not think, therefore you should not be”. As a result the authorities then conclude that fundamental human rights do not apply. As Baroness Warnock once concluded “people with dementia have a duty to die” [4]. Cartesian dualism can lead to (and be used to) support arguments for such tyranny.

The Church’s view: I am, therefore I am. In the Catechism of the Catholic Church (CCC, see excerpts below) we are taught that God made man in his own image, with a unity between body and soul. Man’s unique gift is his ability to “know and love his Creator”. “Man, whole and entire, is willed by God.” The CCC specifically points out that “the term "soul" often refers to human life or the entire human person” and that “The unity of soul and body is so profound that one has to consider the soul to be the "form" of the body.” The Church “teaches that every spiritual soul is created immediately by God - it is not "produced" by the parents - and also that it is immortal: it does not perish when it separates from the body at death, and it will be reunited with the body at the final Resurrection.”

Holy Mother Church clearly takes the view that all humans are human and therefore demand respect, the right to life and full dignity from con­ception right through to death. The soul is beautiful in all stages of human existence, from conception to death. And the disabled are no more nor less human than the most able and intelligent of us. The Church proclaims simply and beautifully that all human life is human and “every spiritual soul is created immediately by God”. That, I think, could be neatly summarised as “we are because we are”.

To be alive and human is enough. With that, we require full respect for our dignity and worth. We must not be expected to “qualify” for our humanity to be recognised. To require that we can feel, that we can experience pain, that we understand, or to require that we somehow qualify in another way for the accolade of being “human” or a “person” simply tyrannises the disadvantaged and disabled.

The ability to think and understand is without doubt a priceless gift of God, but it is not the qual­ifying requirement for anyone to be considered and respected as a human. To be human cannot depend upon a requirement that we think. The human soul is far greater than that.

Within healthcare, as I have attempted to show above, the requirement that people demonstrate abilities before they can be accepted as having “personhood” can deeply corrupt the care of the disadvantaged and disabled, exposing them to poor care, neglect and being killed.

I am, therefore I am” was the Thomistic view and remains the view of Holy Mother Church. We are living beings animated by a rational soul which is our life-principle, not just our intellect and will.


  1. Jones DA . The Soul of the Embryo. Continuum Press 2004. ISBN 987-0-8264-6296
  2. Eckhart Tolle. The Power of Now Hodder and Stoughton. ISBN-13:9780340733509
  3. Ryle (1949) The concept of mind. (London: Hutchinson)
  4. Hill Amelia (2008), Dementia is a living death for 700,000 Britons. That figure is rising sharply. Can we cope? The Guardian Feb 17th
  5. The Diving Bell and the Butterfly. Bauby Jean-Dominique. ISBN-13:9780007790159
  6. “Male and Female He created them” Towards a path of dialogue on the question of gender. Vatican city 2019


I am not a philosopher. I have struggled to work out Cartesian dualism but have been forced to do so by working in a memory clinic with people with all stages of dementia. I am deeply grateful to my severely disabled brother who, taking me by the hand, showed me by his own life, love and sense of humour that his soul was so much greater than his intellect. And I am very grateful to Professor David Jones whose book “the Soul of the Embryo” I have hugely relied upon in writing this article.p>

The Catechism of the Catholic Church and the Human Soul.

These excepts summaries Church teaching on the Human Soul.

  • 355 "God created man in his own image, in the image of God he created him, male and female he created them."
  • 356 Of all visible creatures only man is "able to know and love his creator". He is "the only creature on earth that God has willed for its own sake", and he alone is called to share, by knowledge and love, in God's own life. It was for this end that he was created, and this is the fundamental reason for his dignity:
  • 362 The human person, created in the image of God, is a being at once corporeal and spiritual..... Man, whole and entire, is therefore willed by God.
  • 363 In Sacred Scripture the term "soul" often refers to human life or the entire human person. But "soul" also refers to the innermost aspect of man, that which is of greatest value in him, that by which he is most especially in God's image: "soul" signifies the spiritual principle in man.
  • 364 The human body shares in the dignity of "the image of God": it is a human body precisely because it is animated by a spiritual soul, and it is the whole human person that is intended to become, in the body of Christ, a temple of the Spirit:
    Man, though made of body and soul, is a unity.
  • 365 The unity of soul and body is so profound that one has to consider the soul to be the "form" of the body: i.e., it is because of its spiritual soul that the body made of matter becomes a living, human body; spirit and matter, in man, are not two natures united, but rather their union forms a single nature.
  • 366 The Church teaches that every spiritual soul is created immediately by God - it is not "produced" by the parents - and also that it is immortal: it does not perish when it separates from the body at death, and it will be reunited with the body at the final Resurrection