By Daniel A. Kaufman
On tap this week is the (in)famous first Meditation, from Rene Descartes’ Meditations on First Philosophy. Specifically, I want to draw attention to the logic at the heart of what is – on its own merits – a critique of our claims to knowledge that is both simple and thought-provoking.
Descartes’ self-described aim in the Meditations is to engage in a systematic examination of his belief system, so as to be assured that it rests upon solid grounds. He begins by entertaining a series of skeptical considerations, each more far-reaching in its scope than the last, and by the end, he has managed to cast doubt on every possible variety of belief, whether grounded in sensory experience or in deductive reasoning.
Whichever of the skeptical scenarios we choose and whether we are talking about the justifications we offer, either for empirically grounded beliefs or for beliefs based in reason, there is a common underlying logic to the critique that they provide. So let’s examine each in turn.
- Belief: It’s raining outside.
- Justification: I am looking out of the window, and I can see that it is raining.
In his famous “Dreaming argument,” Descartes points out that one can have exactly the same experience in a dream that one has while awake and that from within the experience, there is no way to distinguish one from the other. Thus, I can dream that I am looking out a window and seeing rain and that experience can “feel” identical to the experience I have, when I am actually looking out the window and seeing rain.
Consequently, (2) is not sufficient as a justification for (1). Indeed, it only provides such a justification, if I can also justify the following:
- Belief: I am not currently dreaming, but really looking out of the window and seeing rain.
The trouble, of course, is that this belief cannot itself be justified by appeal to other sensory experiences – since it is the validity of my sensory experiences that is under question – but it also cannot be deduced or otherwise justified via reason: there is no way, after all, to prove that I am not currently dreaming.
1a. Belief: 2+2=4.
2a. Justification: Some deductive proof (involving the Peano axioms). (1)
In his (equally famous) “Malicious Demon” argument, Descartes maintains that it is possible that our minds are being manipulated by a powerful, malicious being, such that we sometimes – or always – reason incorrectly. Consequently, (2a) is not sufficient as a justification for (1a). It only provides such a justification, if I can also justify the following:
3a. Belief: I am not reasoning incorrectly.
The trouble, of course, is that this belief cannot itself be justified by appeal to reasoning – since it is the soundness of my reasoning that is under question – and it also cannot be justified empirically, insofar as mathematical statements are not known a posteriori.
Too many, when confronting these arguments, have focused unduly on Descartes’ somewhat exotic examples, but they really are entirely dispensable and serve what is essentially an illustrative function. What both arguments rest upon is recognition of the inherent fallibility of our faculties and of the problem of trying to verify the sound exercise of those faculties, by employing the very same faculties.
Notice something else. To the extent that our common belief in the external world and more generally, an objective reality – that is, in a world and reality that exists independently of our minds (and thus, our thoughts and experiences) – is grounded in beliefs that come from sensory experience and reason, we clearly are engaged in a massive exercise in circular reasoning. After all:
- Here is a hand. (Holding out my hand)
only provides evidence for
- The external world exists. (2)
if I already presuppose the external world’s existence.
If I am a disembodied consciousness, living in a perpetual dream, then having a hand-experience is no evidence at all that there is an external world.
Precisely the same argument can be made on the “reason” side of the ledger. And so what we are left with is this – precisely the things that we take as evidence that an objective reality exists, only count as evidence, if one already presupposes that reality’s existence. (3)
Descartes’ solution to these problems, in which he appeals to the divine and the perfection associated with it and its creation, is for obvious reasons unacceptable. My own view is that problems such as these have no solutions and that the value in engaging with them is rather to disabuse us of various notions we may hold about what we know, how well we know it, how good our reasons really are for the things we claim to know, and the like.
- This example of a “proof” for the external world, comes from G.E. Moore’s “Proof of an External World,” Proceedings of the British Academy, 1939.
- This is my paraphrase of Crispin Wright’s “I, II, III” argument, in his “Facts and Certainty,” Proceedings of the British Academy, LXXI.