Ancient and Cartesian Scepticism


In my last article I asserted that I believe in the possibility of knowledge. Against this very possibility, as is well-known, have been urged plenty arguments since antiquity. In the subsequent passages, I shall contemplate both ancient (1) and Cartesian scepticism (2), with a main focus on the latter. The reason for this procedure will only become clear in the course of my future articles wherein I shall continue the enterprise.

1. Ancient Scepticism and Agrippa’s Five Modes

So far as we are willing to maintain justification as a (necessary) criterion for something (a belief, a proposition) to qualify as knowledge, it seems, upon the face of it, the Agrippean Trilemma, comprising the three formal modes of the Five Modes1, applies:

(1) By justifying our beliefs we start an infinite regress because for each justification given, another justification can, in principle, be demanded.
(2) At a certain point, we refuse to continue to justify a certain belief by asserting that it justifiy itself, and thus become dogmatic.
(3) We argue in a circle.

From this, we can form a metadilemma:

(i) We drop justification as a (necessary) criterion for something to qualify as knowledge, so that, regrettably, we allow mere guessing to possibly result in knowledge.
(ii) The Aggripean Trilemma applies.

On this account, it appears as though there is—indeed, can be in principle—no (possibility of) knowledge. As if this were not enough, besides this scepticism dating back to (Greek) antiquity (AS, for short), there is another form of scepticism turning on the possibility of knowledge: Cartesian Scepticism (CS, for short).

2. Cartesian Scepticism

In his famous Meditationes de prima philosophia, René Descartes endeavours to find a steady foundation of belief upon which to build other beliefs, thus yielding knowledge. In order to achieve his aim, he applies methodical doubt to all of his everyday beliefs. Thus, for instance, he considers the difference between being awake and dreaming, concluding that it be, if not impossible in principle, doubtful whether he could be able to know the difference.2 He continues in this manner, doubting even the existence of his very own body, because, he argues, he can conceive of himself being without his body existing at all.3 With respect to the entire outer world’s existence, Descartes assumes, he cannot be certain, since there might, say, be an evil demon deceiving him. He finally reaches the belief that he exist. At this point, he judges that he cannot sensibly doubt his own existence, for his very doubt is a form of thought, and for there to be the possibility of him being thinking, it is a necessary condition that he exist. We can render this argument as follows (where ‘P’ stands for ‘Premise’, and ‘C’ stands for ‘Conclusion’):

P1 For me to be able to think, I must exist.
P2 If I think, I exist.
P3 I think.
C I exist.

It is mostly expressed in the notorious Latin phrase ‘cogito, ergo sum’ (‘I think, therefore I am’). Thus, even if the evil deceiver be misleading him (Descartes) about everything, he (the deceiver) cannot, per impossibile, deceive him (Descartes) about his very own existence, granted, of course, that he (Descartes) can entertain these thoughts. Thus he writes:

[…] Sed est deceptor nescio quis, summe potens, summe callidus, qui de industria me semper fallit; haud dubie igitur ego etiam sum, si me fallit, et fallat quantum potest, numquam tamen efficiet, ut nihil sim quamdiu me aliquid esse cogitabo. Adeo ut omnibus satis superque pensitatis denique statuendum sit hoc pronuntiatum: ego sum, ego existo, quoties a me profertur vel mente concipitur, necessario esse verum.4

[But there is an, I do not know which, almighty and most dishonest deceiver who always diligently misleads me; no doubt, if he mislead me, I (also) do exist, and he deceive me so much as he can, never will he bring it about that I be nothing, so long as I (shall) think that I am something. And so, having considered everything carefully, I come to the conclusion that the expression: I am, I exist, so oft as it be spoken by me, or uttered in mind, is necessarily true.]5

Regarding the outer world (as opposed to the inner, i.e. mental, world), Descartes appeals to his idea of a perfect being, which he identifies with God. Since he himself, so Descartes, is an imperfect being, his idea of a perfect being, God, could not possibly have originated in himself, but must have been instilled in him by God himself.6 If God exist, then, as a perfect being, omnibenevolence belongs to his properties. From this it follows that God would not deceive Descartes, which, in turn, justifies his belief in his senses through which the outer world becomes accessible in the first place. If his senses exist and do not deceive him, and if there, furthermore, be no evil deceiver, because God would neither allow for these scenarios nor would he deceive Descartes himself, then, the outer world must exist. With this reasoning, Descartes rests content, convinced of having established a steady foundation for beliefs upon which to build all other beliefs, thus yielding knowledge.
While many philosophers have endorsed Descartes’ methodical doubt, most have rejected his approach of rebuilding the justification for (true) belief in everything apart from one’s own existence. There are, indeed, many flaws in Descartes’s reasoning. First of all, Descartes presumes that he be one without argument. Even if there be of necessity something which thinks, it need not be only one thinking thing (res cogitans, instead of res cogitantes). Second, having an idea of something, whatsoever it be, does not guarantee the existence of anything apart from one’s own existence. Third, how does he know that his very existence, as a brute fact, be not intrinsically perfect, being thus able to conceive of whatsoever may be possible, perhaps even thereby bringing it about?7 Fourth, why should we acknowledge that being perfect entails being omnibenevolent? Would it not rather be more plausible to suppose that a perfect being would be disinterested, that is, neutral? Also, we might take it that a perfect being may be omnimalevolent instead of omnibenevolent. We can, by the way, define ‘being perfect’ also negatively, namely as ‘possessed of no flaws, never making mistakes, etc.’ This defnition, however, would not imply attributes usually ascribed to God (with a capital g), namely, omnipotence, omnipresence, omniscience, omnibenevolence. As is apparent from his Discours de la méthode, as well as from his ‘epistola’ [letter] to the ‘SAPIENTISSIMIS/Clarissimisque viris/SACRAE FACULTATIS/Theologia Pariensis Decano et Doctoribus’ [very wise and illustrious men, the dean and the teachers, of the sacred faculty of theology in Paris]3, Descartes presupposes both the existence of the Christian god and the attributes usually ascribed to him, thus presupposing what he sets out to prove in the second place; which in its turn he uses as the very foundation of justification for his belief in the external world, which cannot succeed if his foundation is flawed—which it is—, so that he, as to this part of his endeavour, fails to accomplish what he sets out to prove in the first place.

Interestingly, despite his intention of establishing a steady foundation for knowledge, which motivated the Meditationes in the first place, Descartes appears to have enforced scepticism of knowledge. The burden of proof always rests upon those who assert a proposition, not upon those who deny it. Recall, though, that thus far we have not concerned ourselves with the question of what, in fact, knowledge be, that is to say, we have not given an explicit definition. Both this aspect and my suggestion for a strategy against scepticism will be the concern of my next article.

1. Confer the entry in Stanford Encyclopedia of Philosophy:”.
2. Descartes, René: Meditationes de prima philosophia, Lateinisch-Deutsch; Hamburg: Felix Meiner Verlag, 1992; Meditatio I, 5, pp. 32-34 [All further citations and references are from/to this edition (Meditationes, for short).]
3. Meditationes, Meditatio II, 6, pp. 46-48.
4. Op. cit., Meditatio II, 3, pp. 42-44. (Emphases in the original.)
5. English translation by me; the translation follows the original Latin text so far as the different structures of both languages allow.
6. Meditationes, Meditatio III, 15-24, pp. 74-82.
7. To be fair, Descartes takes these possibilities into consideration in the process of Meditatio III, 15-24; yet, first, as the main text above says, he conspicuously presupposes the Christian god’s existence, and second, for the alleged inference, he appeals to the notion of causality (nothing can bring about something greater, in the sense of better or more accomplished, than itself) which is an empirical notion. For this reason, his argumentation concerning this part of the Meditationes is flawed.


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