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Gordon Kennedy

The Significance of Philosophical Scepticism

In answer to the question 'What can we know?' anyone who gives a pessimistic answer is labelled a sceptic. Scepticism is associated with incredulity. A sceptic is someone who questions things (particularly received opinions) and also practices suspension of judgement. This questioning outlook has been labelled by some as practical scepticism. However, philosophical scepticism involves more than this. Its essential element is a general view about human knowledge. In the broadest terms, philosophical scepticism holds, or at least finds irrefutable, the view that knowledge is impossible.

There are two features of philosophical scepticism which differentiate it from everyday 'sceptical' outlooks. The first has to do with its strength. The more challenging sceptical arguments do not depend on imposing high standards for knowledge or justification. Rather, the scepticism they imply is radical. It is not just the case that we can have all kinds of good reasons for what we believe, though those reasons do not quite measure up to the standards required by genuine knowledge. The radical sceptic questions whether we ever have the slightest reason for believing one thing rather than another, so we can never even get to the point of justified belief, never mind whether our justifications are sufficient for knowledge, in some more restricted sense.

The second crucial feature of philosophical scepticism concerns its scope. The philosophical sceptic's negative verdict on human knowledge is highly general. This generality explains why philosophical scepticism formulates its challenge in terms of the possibility of knowledge. it is not merely the case that we in fact know a good deal less than we like to think but rather that aspiring to knowledge is inherently problematic. The concern is not just that we don't know all that much but that we can't. The strength and scope of philosophical scepticism are connected with the simplicity and intuitiveness of sceptical arguments, which are radical and general because they exploit only 'lowest common denominator' features of knowledge.

Another characteristic of philosophical scepticism is that it offers initially plausible arguments for its sceptical conclusion. They are plausible in that not only do they display no obvious logical flaws, they seem to involve only the simplest and most mundane considerations. They appear to be highly intuitive. This apparent intuitiveness is crucial to scepticism being such an intractable problem. If sceptical arguments were obviously dependent on controversial or implausible theoretical ideas, scepticism would not be a surprising verdict on our aspirations to knowledge but simply a consequence of some regrettable, theoretical missteps. This is in fact what makes sceptical arguments philosophically interesting. They present us with a line of reasoning that we ourselves find intuitively plausible, but which leads to a conclusion that we find absolutely implausible. The task then, for those epistemologists who think that scepticism is based on a mistake, is to identify and explain the mistake.

The implication of philosophical scepticism is that, rationally speaking, we can believe anything or nothing. This highlights the huge gulf between philosophical scepticism and ordinary 'everyday' scepticism. The 'everyday' sceptic does not necessarily believe that the quest for knowledge is impossible, but rather thinks that most people's standards of credibility are too low or laxly applied. He will suspect that what are advanced in terms of knowledge are really just opinions held for no good reason at all. In consequence, his scepticism will be demanding and selective. But philosophical scepticism, as radical and general, undermines the very epistemological distinctions on which everyday scepticism depends. Accordingly, it is not simply different from but precludes scepticism of the 'everyday' kind. A common approach by many philosophers is to assume that scepticism of this kind is wrong, and to concentrate on the question of where the sceptic goes wrong, or more exactly, where certain sceptical arguments go wrong. In this way, the motivation for engaging sceptical arguments is methodological. The point of this approach is that it is simply not possible to doubt everything since this would lead to epistemological nihilism and solipsism, therefore the strategy centres on what rational arguments can be raised for the negation of total nihilism and the use of practical scepticism.

Moving to a more specific look at how an individual philosopher assesses philosophical scepticism, A.J. Ayer, in 'The Central Questions of Philosophy', states that the aim of the sceptic is to demonstrate the existence of an unbridgeable gap between the conclusions which we desire to reach and the premisses from which we set out. For example, in the case of our belief in the existence of physical objects , the sceptic will claim that the only premisses which are supplied to us are propositions which relate exclusively to our sense impressions. But then, he argues, since the conclusion of a valid deduction can contain no reference to entities which do not already figure in its premisses, there is no deductive passage from propositions of this sort to propositions which relate to physical objects. It must, therefore, be an inductive inference, one in which the conclusion goes beyond the premisses, as when we advance to an empirical generalization on the basis of observing that it holds good in a number of particular instances.

But the argument continues, to the extent that this form of reasoning is legitimate at all, it can carry us forward only at the same level. As a generalization from past experience, it can enable us to predict the occurrence of future sense impressions on the basis of those that we have already had, but it cannot lead us to a conclusion which we could not conceivably verify: it cannot justify a passage from the occurrence of sense impressions to the existence of anything which is not an object of experience. But then, the sceptic concludes, if our belief in the existence of physical objects cannot be justified either by a deductive or by an inductive argument, it does not have any rational warrant. It is clear that the same form of argument can be applied to other cases in which our access to the objects or events of which we claim to have knowledge can plausibly be represented as being only indirect.

A.J. Ayer shows that it is possible to characterize different philosophical standpoints by their acceptance or denial of different steps in the sceptic's characteristic form of argument. For example, those who are known as Naive Realists deny the first step of all. They maintain that we perceive physical objects not through a screen of sense impressions but directly, that we can under favourable circumstances have direct access to the experiences of others, that memory can yield direct knowledge of the past. In short, they deny that there is any gap to be bridged. In the case of the problem of induction the gap is abolished by the claim that we are capable of apprehending necessary connections between events.

Reductionists accept the sceptic's starting point, but deny the second step in his argument. They represent the transition from evidence to conclusion as proceeding at the same level by bringing the conclusion down to the level of the evidence. Thus, they follow Berkeley and Mill in holding that statements about physical objects are translatable into statements about sense impressions.

What Ayer describes as the 'Scientific' approach consists in accepting the first two steps of the sceptic's argument but denying the third. For example, the existence of physical objects is represented as a probable hypothesis which one is justified in accepting because of the way in which it accounts for one's experience. In the same spirit philosophers of this way of thinking may try to make a case for the acceptance of certain principles which will underwrite the attribution of at least a high degree of probability to some of our judgements about the future.

Yet another stance is taken by those who accept all three steps in the sceptic's argument but deny that they entail a sceptical conclusion. The position most commonly taken here is, that in insisting that our beliefs be justified either deductively or inductively, the sceptic is presenting us with a false dilemma. He overlooks the fact that these are not the only ways in which a proposition can be related to what we call its evidence.

The question which we have to answer in each instance is which, if any, of these approaches is correct. And in order to do this we have to give an account of the propositions which the sceptic puts in jeopardy.

Another quite different approach to the problem of philosophical scepticism is that adopted by Ludwig Wittgenstein, considered by many to be one of the most influential philosophers of the twentieth century. One of his main philosophical outlooks was that insight is gained by attempting to neutralise sources of philosophical confusion rather than by attempting to construct quasi-scientific theories of philosophical conundrums.

A passage in his work Tractatus Logico-Philosophicus which states his position on scepticism is given as follows : (section 6.51)

From the above quotation we can see that Wittgenstein attempts to dissolve the problem of scepticism by showing it to be senseless or meaningless. An example of this might be shown by the well known problem of a person who believes himself to be always dreaming. According to Kober, Wittgenstein's solution in this case it would be to regard such an all-encompassing doubt as senseless, since in the case of permanent illusions alleged perceptions can neither be unmasked as illusory,(in other words there is no question), nor definitely established as veridical.(i.e. there would not be an answer.)

In sum philosophical scepticism has been a central concern of the theory of knowledge. Some philosophers think that, without the problem of scepticism, we would not know what to make of the idea of distinctively philosophical theories of knowledge.


Audi, Robert. (Ed.). The Cambridge Dictionary of Philosophy. Cambridge University Press.(1995). pp. 237-238.

Ibid. pp. 738-742.

Ayer, A.J. The Central Questions of Philosophy. Penguin.(1973). Chapter 3. pp. 58-67.

Ibid. Chapter 7. pp. 137-140.

Bostrom, Nick. What we should say to the Skeptic. http://www.hedweb.com/nickb/skepticism.htm

Greco, John. The Blackwell Guide to Epistemology. (Eds. Greco, J. and Sosa, E.). Blackwell.(1999). Introduction. pp. 1-31.

Kober, M. in The Cambridge Guide to Wittgenstein. (Eds. Sluga, H. and Stern, D.G.). Cambridge University Press. (1996). Chapter 13, pp 411-441.

Mautner, Thomas. (Ed). Penguin Dictionary of Philosophy. Penguin Reference.(1996). pp. 502-503.

Morton, Adam. Philosophy in Practice %#151; An Introduction to the Main Questions. Blackwell.(1996). Chapter 1. pp. 3-35.

Moser, Paul. The Blackwell Guide to Epistemology. (Eds. Greco, J. and Sosa, E.). Blackwell.(1999). Chapter 2. pp. 70-91.

Scruton, Roger.Modern Philosophy — An Introduction and Survey. Mandarin.(1994). Chapter 2. pp. 16-22.

Shermer, Michael. A Skeptical Manifesto. The Skeptic, vol. 11, Spring 1992. pp. 15-21.http://www.skeptic.com

Warburton, Nigel. Philosophy — The Basics. Routledge.(1992). Chapter 4. pp. 93-111.

Williams, Michael. The Blackwell Guide to Epistemology. (Eds. Greco, J. and Sosa, E.). Blackwell.(1999). Chapter 1. pp. 35-69.

Wittgenstein, Ludwig. Tractatus Logico-Philosophicus. (Translated by Pears, D.F. and McGuinness, B.F.). Routledge. (1961). Section 6.51, p73.