Global Scepticism Under Scrutiny


Someone might try to defend a coherence theory of truth without defending a coherence theory of knowledge, perhaps on the ground that the holder of a coherent set of beliefs might lack a reason to believe his beliefs coherent. This is not likely, but it may be that someone, though he has true beliefs, and good reasons for holding them, does not appreciate the relevance of reason to belief. Such a one may best be viewed as having knowledge he does not know he has: he thinks he is a skeptic. In a word, he is a philosopher.1

Parenthisizing the context of the coherence theory of truth and knowledge, with these words Donald Davidson neatly characterizes (all) philosophy as scepticism in a similar manner as I did in my ‘Philosophy and Scepticism’2. Thus, a philosopher is someone who will not believe something on mere purportion, but will instead investigate whatever may draw his attention to it.
There is, however, the question how far scepticism can sensibly reach. In other words, scepticism itself needs legitimate justification for its very own enterprise. As the title suggests, I shall concentrate on the legitimacy of global/universal scepticism (‘global scepticism’ hereafter) in this paper. For the purpose of eliciting the relations among the different aspects and standpoints, I decided not to subdivide the paper. Instead, I shall present one long discussion, and summarize its results in a short conclusion at the end of the paper.

The Legitimacy of Global (Universal) Scepticism

To be sure, nowadays most, especially radical, forms of scepticism, such as global scepticism, are usually only conceived theoretical positions whereto one tries to answer instead of holding such a standpoint oneself. Notice that trying to answer someone, and be he only an imagined adversary, entails admitting that he have a point deserving to be taken seriously, and therefore also deserving to be taken into consideration. To be doubtful is, in the first place, a virtue – given experience, of course, and this, quite obviously, may already pose a problem, for we, or our imagined sceptical adversary, may be unwilling to accept experience as a presupposable datum. Now, if we reject experience as a suitable origin of reliable information (in the broadest sense of the word), we are left with so-called a priori grounds. But to reject experience as good grounds for knowledge, requires an appropriate argument which actually refutes the assumption. It would be an illicit step to reject an assumption with prima facie plausibility in favour of another assumption lacking such plausibility. So how does the sceptic argue in order to justifiably reject (i.e. refute) experience as an appropriate source of knowledge?
A starting point is often made by querying sense perception. We already encountered this scepticism in Descartes’s reasoning whether one could ever distinguish dreaming from being awake. Descartes himself concluded that we never could, and thereby had to let go of experience relating to the external world (i.e. relative to the mind as the inner world) as an adequate source of knowledge.3 To me, this conclusion appears quite implausible, since people, including myself, are usually able to tell a dream, or an experience made in a dream, from experiences they make when they are awake. Dreams never have the same experiential quality as experiences made while being awake.
Notwithstanding this qualitative difference, the sceptic may argue, granted that we can tell such a difference, we nevertheless cannot justifiably say which is which, that is, we cannot find out whether what we call ‘being awake’ and ‘being asleep and dreaming’ really are what we presume them to be, or vice versa.
But wait, we are already engaging in a debate with the sceptic (regardless of whether it be the sceptic in ourselves, an imagined adversary, or a real person) as though we had accepted that he have a good point which deserves to be taken seriously. I am much in sympathy with George H. Smith, when he writes:

Universal skepticism is usually stated in one of two ways. In its positive form it consists of the doctrine that man can know nothing. This belief can be easily dismissed, because anyone who defends it finds himself immersed in hopeless absurdities. In asserting that there is no knowledge, the skeptic is asserting a knowledge claim—which according to his own theory is impossible. The universal skeptic wishes to claim truth for a theory that denies man’s ability to arrive at truth, and this puts the skeptic in the unenviable position of uttering nonsense. Indeed, he cannot even begin to argue for his position, because the “possibility of knowledge is presupposed in the very possibility of argument, in the very possibility of having recourse to reasons.”4

As I wrote elsewhere5, the sceptic cannot simply allow a proposition to be true, while not allowing other unjustified propositions to be true. Needless to say, if the proposition that man can know nothing except for his inability of gaining any knowledge above this one proposition were true, no further proposition could be true ex hypothesi. There is, however, no reason why we ought to accept this. If some proposition can be true, why should it exactly be the sceptic’s?
Smith, citing Francis Parker, points out that if there be any assertion in the first place, it be necessarily true that there be the possibility of knowledge.6
The second possibility, according to Smith, for the sceptic is to weaken his claim to demanding that man have to doubt every purported instance of knowledge. This claim, though, reduces to the purportion that man can never procure certainty, against which the immediate objection arises that if it were true, the sceptic’s claim itself would be necessarily open to doubt, with the result that there would be, again, no reason to accept it as true.7 To the question why we ought to doubt each knowledge claim the sceptic may well respond that man be capable of error. The very concept of error, however, presupposes the opposite concept of truth.8 Stated differently, in order to be able to determine that and when something be false, one needs to be able in advance, or at least at the same time, to determine that and when something be true, and vice versa. So merely stating that man be fallible – for this is whereto the sceptic’s claim reduces – does not suffice to infer that man can never gain certainty or truth. An infallible being, it goes without saying, would be in no need of any justifable grounds for its beliefs, and for this reason a science of knowledge, epistemology, would be useless to it. Yet since man is fallible, he needs a science of knowledge. ‘The skeptic’, writes Smith relating to the sceptic’s purportion, ‘thus turns epistemology on its head by using the foundation for a science of knowledge—human fallibility—as a weapon to argue, in effect, that a science of knowledge is impossible for man.’9 The fallacy the sceptic thus commits is to equate knowledge and certainty with infallibility.10 Therefore, both the strong and the weakened stance of global (universal) scepticism are untenable.
In the next section (‘III The Contextual Nature of Knowledge’), Smith further increases the pressure on the sceptic by quoting both Thomas Reid and J. L. Austin, each giving lively examples which render global scepticism irrational. The former compares the sceptic’s claim, which, in effect, assumes that reason can defeat itself, with a man who in terms of his own allegedly clear sight asserts that he himself and all other men be blind. The latter, then, calls to mind the inherent liability of machines to break down, which, all the same, does not preclude good machines from working reliably, that is to say, good machines seldom break down despite their inherent liability to do so.11
As I wrote myself in ‘Justification Under Scrutiny’12, and Smith, with reference to Reid, Austin, and D. W. Hamlyn, writes, too13, global doubt needs justification. Justification, in turn, however, is only obtainable within a contextual frame. The sceptic, then, wants to attack the possibility of knowledge from outside such a contextual frame, which is, unfortunately for him, an invalid move.
At this point, I skip some ensuing pages of Smith’s discussion because, first, it pertains, for its most part, to religion, which is not the current paper’s topic, and, second, because I want to return to our initial theme of scepticism as to sense perception. Smith dedicates an entire section to this issue in form of a dialogue between a sceptic and an antisceptic, again with much reference to religion, as the book’s main theme suggests. The details will not concern us here – this would be impossible in a short paper like the present one anyway –, so suffice it to summarize its results significant for the present investigation.
The main aspect of the section ‘V Skepticism and Sense Perception’14, then, is that the sceptic appeals to concrete instances of sense perception to refute the very same thing. The sceptic will, to illustrate, usually say something like ‘On occasion o1 something a1 will look F1 to you, whereas on occasions o2, o3, …on it may look quite differently to you, say, F7, F19, F53, …Fn. You may even, on some occasion on, mistake a1 for something completely different, say, a104. Therefore, you cannot rely upon your sense perceptions, and, as a corollary of this, your sense perceptions cannot yield knowledge.’ To put it more concretely, ‘Upon some occasion, an object may look red to you, whereas upon other occasions it may look quite differently to you, say, a darker shade of red, brown, black, and so on. You may even mistake it on some occasion for a totally different object, for example, you may mistake your friend Susanna for your cousin Nicole. Therefore, you cannot rely upon your sense perceptions, and, as a corollary of this, your sense perceptions cannot yield knowledge.’
So far so good. The reasoning in itself is logically consistent, as we can see from a somewhat simplified but not distorted formalization. For the sceptic’s argument is a simple modus ponens (where ‘P’ stands for ‘premise’, and ‘C’ stands for ‘conclusion’):

P1 ~p → ~q
P2 ~p
C ~q

Let ‘p’ represent the proposition ‘Sense perceptions are reliable’, and ‘q’ the proposition ‘Sense perceptions yield knowledge’, so that (Scmp) reads as follows. ‘If sense perceptions are not reliable, then, sense perceptions do not yield knowledge. Sense perceptions are not reliable. Therefore, sense perceptions do not yield knowledge.’
The sceptic’s argument is clearly formally valid. Given that if sense perceptions are not reliable, then, sense perceptions do not yield knowledge, and given that sense perceptions are indeed not reliable, it follows that sense perceptions do not yield knowledge. The flaw of this argument lies in the sceptic’s appeal to sense perception, of which he just asserted that it cannot yield knowledge, in order to justify a knowledge claim himself. But the sceptic must not employ sense perceptual experiences in order to refute sense perceptions, since sense perceptual experiences imply sense perceptions by definition. The scepctic’s claim is, once more, illicit.
The sceptic may, of course, try another, slightly different, move, as taken by the sceptic in Smith’s dialogue. Namely, he may purport that if one and the same object, a pencil in this case, when it is held in the air, for example, compared to when it is held under water, can look different to one, this gives rise to a contradiction. The same thing, says the sceptic, cannot be straight, as it looks when held in the air, and bent, as it looks when held under water.15
The antisceptic is, rightly, quick to point out that this does not violate the Law of Contradiction at all. He, the antisceptic, has acknowledged that the same pencil does look differently on different occasions but not that it actually be different. Furthermore, the Law of Contradiction says that one thing a cannot be F and not-F at the same time and in the same respect. The example of the pencil looking straight when held in the air, and looking bent when held under water, refers to different times and different respects, however, and thus does not prove sense perceptions to bring about contradictions.16 Smith’s antisceptic concisely formulates the point thus:

[…] In other words, it is through our senses that we gather the information with which to explain why the same object appears differently under different conditions. We solve the alleged instances of ‘sensory deception’ through a further appeal to sensory evidence—just as you [the scepctic] must presuppose the validity of the senses in the very attempt to disprove the validity of the senses.17

The debate continues for a while with further futile attempts by the sceptic to disprove the validity of sense perception. The conclusion is obvious: If the sceptic cannot disprove the validity of sense perceptions by a different approach than presuming the very same thing he sets out to disprove, then, he fails to show how global scepticism can be a legitimate, that is, valid, standpoint. Since it is impossible to prove sense perceptions principally invalid other than by implicit appeal to their validity, global scepticism of sense perceptions is untenable.


As we have seen, although global scepticism appears to have some plausibility on the face of it, it is in fact an untenable position. Neither such a scepticism concerning knowledge in general, be it in a strong or weakend form, nor a scepticism of this sort with regard to sense perception as a source of knowledge succeed in even getting off the ground, because they inadvertently must take as a precondition the very thing they set out to disprove. Thus, one mistake of global scepticism pertaining to knowledge in its strong form is that knowledge must be possible if a claim like the sceptic’s, namely, that knowledge be impossible for man, shall be able to be true, for then it is, as of necessity, a knowledge claim. The other mistake is the equation of knowledge and certainty with infallibility. The latter objection, of course, applies as well to the weaker claim that man can never be certain as to any proposition, and therefore must doubt each knowledge claim. For if man can never be certain with respect to any proposition whatsoever, then, the sceptic’s position must be open to doubt, too.
The mistake of global scepticism relating to sense perceptions, on the other hand, is, quite similarly, that it presupposes sense perceptions’ validity in order to disprove sense perceptions’ validity. Since there is no other possible approach, this kind of scepticism also fails.
Now, if neither global scepticism as to knowledge, be it in its strong or weaker form, nor as to sense perception, that is to say, at the very foundations of knowledge in the first place, succeed, global scepticism is untenable in principal. The refutation of global scepticism, of course, does not necessitate pure credulity. In fact, scepticism of a moderate sort can be – and indeed is – an important and effectual tool for attaining knowledge and distinguishing sense from nonsense. This remains a topic to pursue at another time and place.

1. Davidson, Donald: ‘A Coherence Theory of Truth and Knowledge’, p. 137 in Davidson, Donald: Subjective, Intersubjective, Objective; Oxford: Oxford University Press 2001, reprinted 2002.
2. Confer: ‘Philosophy and Scepticism’:
3. Confer: Descartes, René: Meditationes de prima philosophia, Lateinisch-Deutsch; Hamburg: Felix Meiner Verlag 1992; Meditatio I, 5, pp. 32–34 and my ‘Ancient and Cartesian Scepticism’:, 2. Cartesian Scepticism, first section.
4. Smith, George H.: Atheism: The Case Against God; Amherst, New York: Prometheus Books 1989, p. 131. [All following citations and references are from/to this edition, Atheism, for short.]
5. Confer my ‘Justification Under Scrutiny’:, 3. Endless Justification of Justification?.
6. Confer: Atheism, p. 131.
7. Confer: Op. cit.
8. Confer: Op. cit., p. 132.
9. Confer: Op. cit., p. 133.
10. Confer: Op. cit., p. 134.
11. Confer: Op. cit., p. 135.
12. Confer: ‘Justification Under Scrutiny’:, 3. Endless Justification of Justification?
13. Confer: Atheism, p. 136.
14. Confer: Op. cit., pp. 147-162.
15. Confer: Op. cit., pp.151-153.
16. Confer: Op. cit., pp. 152-153.
17. Op. cit., p. 153.


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