The radical sceptical hypothesis cited in the question above has been a source of epistemic frustration since the time of Plato, and has gripped philosophical interest through Sextus Empiricus, Michel de Montaign, up to Descartes whose Method of Doubt employs the most famous formulation of the Dreaming Argument, which goes from an unexceptional premise to the extraordinary conclusion that we have no knowledge at all. The claim in question seems insuperable from a philosophical sceptical standpoint; notwithstanding, there have been serious attempts to refute the sceptic, each with varying degrees of success. However, it seems that almost every attempt at dodging the bogey of scepticism has, by the highest epistemic standards, failed. In this essay, I will consider the arguments that have been raised to meet the sceptic head on, and discuss their strengths and limitations.
The sceptic’s argument suggests that anything possible to experience in one’s waking life is also possible to experience as a dream, as we can have experiences that are indistinguishable from waking whilst fast asleep. The premise (D), “It is impossible to tell whether one is dreaming” in conjunction with the traditional tripartite analysis of knowledge would render any knowledge impossible. According to the sceptic, if you cannot be certain that (D) does not obtain, you cannot possess justification for any of your beliefs. For example, a proposition such as, “I am at my desk writing this essay”, is not justified, since the possibility that I am not in fact asleep and dreaming cannot be eliminated. The dreaming argument can be better analysed when it is broken down into its constituent premises and conclusions:
1.) I have had dreams which were experientially indistinguishable from waking experiences. 2.) So the qualitative character of my experience does not guarantee that I am now not dreaming, then I can’t know that I’m now not dreaming. 3.) If the qualitative character of my experience does not guarantee that I’m now not dreaming, then I can’t know that I’m now not dreaming. 4.) So, from 2 and 3, I can’t know that I’m now not dreaming. 5.) If I can’t know that I’m now not dreaming, then I can’t know that I’m not always dreaming. 6.) So, from 4 and 5, I can’t know that I’m not always dreaming. 7.) If I can’t know that I’m not always dreaming, then I can’t know to be true any belief about the external world which is based on my experience. 8.) So, from 6 and 7, I can’t know to be true any belief about the external world which is based on my experience.
The first and most obvious point of contention is the truth of premise 1: that dreams are experientially indistinguishable from waking experiences. J.L. Austin denies the truth of this premise, arguing that since we have the expression, “a dream-like quality” there must be a special quality that dreaming experiences possess which waking experiences lack, if the expression is to possess meaningfulness. The only explanation for this description and differentiation between waking and dreaming states is that the qualitative character of dreams is different from that of waking experiences. However, the sceptic can reply to this claim by establishing that there are two kinds of dreams, those which are hazy and obscure, possessing the so-called “dream-like quality” and those that are vivid and pellucid; it is this second kind of dream that is being adduced in the sceptic’s radical hypothesis, thus the sceptic deflects the knower’s refutation. However, G.E. Moore is also keen to deny the sceptic his first premise. Moore’s argument states that in the mere offering of the sceptical argument, the sceptic is implicitly committing himself to know that the premises are true. Henceforth, if the argument is valid, then by its own conclusion, the sceptic...