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Discourse on Descartes’ discourse.

In this book Rene Descartes is attempting to create a method of understanding and investigation guided by pure reason, that is, by intuitive, deductive logic to investigate the world, that is separate from the less definite sense experience.

One of the most striking parts of Descartes method, is his notion of absolute certainty – Descartes tells us:

we reject all knowledge that is merely probable, and we decide to believe only in what is known perfectly and cannot be doubted. (Descartes, Discourse on Method and Related Writings, p. 119, 1637)

Descartes does not accept probabilistic arguments, they merely “increase the number of their doubts” (p. 120) and do not lead to “scientific knowledge” (p. 20). It is the intellect alone, via clear intuition and deduction (p. 163)  that leads to certain knowledge, and that sensation, imagination and the memory can aid or hinder this process (p. 143).

To Descartes all we are left with, which we can hold to absolute certainty, is “arithmetic and geometry” (p. 120), which are alone free from “every taint, falsehood or uncertainty” (p. 120). To Descartes, a robust epistemology contained reliable knowledge by 2 routes – experience and deduction, although he rejected experience as it is often deceived, whereas deduction, which he described as “pure inference of one thing from another” (p. 120) can never be performed badly by a minimally rational intellect. (Descartes, Discourse on Method and Related Writings, p. 120, 1637)

Of course most people would agree that mathematics is one thing of which our answers we can be certain, that much I would not contend with Descartes, but I would ask, that if Descartes is only interested in the kind of certainty with which we can achieve with mathematical knowledge, how is it possible that we could come to the same kind of certainty about anything else, using this epistemology?

One should conclude from all this, not that arithmetic and geometry alone should be studied, but only that, in seeking the right path to the truth, one should not be concerned with any object about which one cannot have as much certainty as in the demonstrations of arithmetic and geometry. (Descartes, Discourse on Method and Related Writings, p. 121, 1637)

A startling admission really, after all, what other piece of knowledge can we attain that has such certainty? Logic? Moreover, Descartes, when coming to his initial breakthrough of “I think, therefore I am” on p. 24-6 admits the road that took him to this place was that his senses and reason could be deceived:

Thus because our senses sometimes deceive us, I decided to assume nothing was the way senses made us imagine it. And since there are some people who make mistakes in reasoning and commit fallacies, even in the simplest geometrical proofs, and since I thought I was as subject to mistakes as anyone else, I rejected all false arguments that I previously accepted as demonstrations. (Descartes, Discourse on Method and Related Writings, p. 24, 1637)

Whatever led Descartes to initially question reason, even the certainty of mathematical proofs, seemed reasonable to me. I  agree with Descartes when he says that reason can be deceived – he believes it can lead us to absolute and certain truth, the problem of course being, that some of the reasoning Descartes made, was wrong viz. his claims of animals to be like that of ‘automata’. Descartes claimed that animals posses only the imitation of life, that their expressions of pain, fear etc were like subroutines in a computer, nothing more. This (incredibly dangerous, wrong-minded and harmful) idea came from his conception of God – to Descartes the animals represent simple machinery, as we would create, but they are infinitely more adept at imitating life, as they were created by the ultimate creator – God. This seems to me, to be a clear case of reason, being deceived, by faulty assumptions. Yes, he might have had a certain conclusion to his mind, but in reality?  (Descartes, Discourse on Method and Related Writings, p. 72, 1637)

Descartes method was supposed to lead him to absolute truth, but the truth of his assertions regarding animals are by no means clear or certain  (see here, hereherehere for some empirical examples). One could argue that this does not prove Descartes wrong, to which I think, this would be a fair rebuttal. I would also add, “proving” that animals do not suffer (especially to absolute certainty) is a non-falsifiable hypothesis (thankyou Dillahunty – see comments section), which depending on what type of epistemological strata you hold to – it makes Descartes hypothesis meaningless, useless, or vapid. Descartes also reasoned, erroneously, that the body runs on heat provided from the soul via God (p. 33-9), which is also seemingly non-falsifiable.

Descartes critique of sense experience – that our experience of light “which is informed in our imagination by our eyes” (p. 85) or words which “do not in any way resemble the things they signify” (p .85) asks us to review the very way we perceive the world:

Now if words – which have meaning only as a result of a human convention – are enough to make us think about things that do not resemble them in any way, why is it not possible that nature may also have established a particular sign which would make us have the sensation of light, even though such a sign contains nothing in itself that resembles the sensation? (Descartes, Discourse on Method and Related Writings, p. 85, 1637)

What is possible is not necessarily what is probable, do we have any reason to think that light doesn’t exist based on our perception of it, or that nature is represented as Descartes begs us consider? Even if it is, this solipsistic idea does not mean we also exclude sense experience, moreover, it adds nothing to our way of life to assume solipsism as true – yes it is logically possible that I am a brain in a vat, but pain feels real, hunger feels real – the effects of this life are perceived as real. Until we have any evidence to suggest reality is not the way we perceive (and by ‘perceive’ I also mean by what we can corroborate using science) this kind of abstract musing is only taking us to absurdity. Hume disagrees with Descartes in A Treatise of Human Nature:

… whereever by any accident the faculties, which give rise to any impressions, are obstructed in their operations, as when one is born blind or deaf; not only are impressions lost, but also their correspondent ideas; so that there never appear in the mind the least traces of either of them. Nor is this only true, where organs of sensation have never been put into action to produce a particular impression. We cannot form ourselves a just idea of the taste of pineapple, without actually having tasted it. (Hume, A Treatise of Human Nature, p. 53, 1739)

There is no reason without sense experience, after all, how would we imagine or reason about anything when we have no sense experience to give us the tools to reason about  it (‘it’ being colour, shape etc)?  This does not necessarily mean we value sense experience over reason, why? As we’ve seen, we can still reason ineffectively, and come to wrong conclusions, as Descartes did with his investigations of animals (and he was of “minimally rational intellect”). How are we supposed to operate in a world, which feels real, despite whatever may be really going on, if we have no epistemological tools to work in it? We want a worldview that views the world accurately, includes all the evidence, not simply a selective portion of it.

This philosophy seems largely solipsistic or rather, the results of such lead to solipsism, for those who don’t know what that is:

The belief that only ones self and one’s experience exists. solipsism is the extreme consequence of believing that knowledge must be founded on inner, personal states of experience, and then failing to find a bridge whereby they can inform us of anything beyond themselves. (Blackburn, The Oxford Dictionary of Philosophy, p. 343, 2008)

In this conclusion Descartes has built from deduction, and reason, absolute, inviolable truths. That for me is where the problem lies, a worldview, and epistemology, includes all methods of reason, investigation and routes to knowledge, that produce reliable, results. I have no problems with the use of reason, I think it’s valid, but I also think that we should use empiricism too, and that’s its truths, where backed by reason, evidence etc, give us a more appropriate and full sense of reality.


Blackburn S. (2008).  The Oxford Dictionary of Philosophy (2nd Edition).  New York. Oxford University Press. P. 343.

Descartes R. (1637). Discourse on Method and Related Writings (This translation first published by Penguin Books 1999). London. The Penguin Group. Pp. 72, 85, 119, 120.

Hume D. (1739). A Treatise of Human Nature (This translation first published by Penguin Books). London. The Penguin Group. P. 53 .

Categories: Philosophy, Skepticism, Theism
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