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A common skeptical argument aims to show that since I can't know that some strange hypothesis (e.g. that I am dreaming right now or that I am a bodiless brain in a vat being stimulated by diabolical super scientists to believe that I have a body and live in Southern California or...) is false, I don't really know anything at all. René Descartes is of course the most notorious presenter of this argument (and also perhaps the one most duly noted for his failure to answer it). The trouble with this kind of argument is that it very easily induces a kind of intellectual trance. It invites the unsuspecting undergraduate into its cozy little Tumnusian den, and, after what seem like a few brief moments, she awakens to find herself locked in a world of confusion and doubt with seemingly no way to get back home before the queen of that twisted world comes and claims her mind forever.
But, thanks be to God, ninety minutes pass, and she is back in her world (which may not be real but is at least familiar) of text messages and status updates. The spell is broken. But how was it broken? David Hume would say that "custom (or habit)", nature herself, has asserted itself and forced the formerly bamboozled youth to ignore the flawless demonstration of her ignorance and to go on living the life of a presumptuous commoner. But I say Hume is wrong about that. Not because I think that I can prove I am not dreaming or that I am not a brain in a vat or [name your favorite skeptical hypothesis], but because I believe that there are more ways to know than only by reason. In fact, we only know things by reason in a roundabout way, through inferential processes which are ultimately based on knowledge that is known by heart. Everyone, even the skeptic, assumes an entire battery of basic principles in forming their arguments for this or that conclusion - truths of logic, mathematics, the external world, other minds, the past, ethics.
Skeptical arguments will never be answered by rigorous argument because the skeptics are right! Reason, as they understand it at least, is unable to account for our knowledge that we are not massively deceived. Since reason is thus impotent, they conclude we do not know anything, but they are wrong about that! "We know," as Michael Polanyi says, "more than we can tell" (The Tacit Dimension [1967], 4). Or Pascal:
We know the truth, not only through reason, but also through the heart. It is through the latter that we know first principles, and reason, which has no part in it, tries in vain to challenge them. The skeptics, who have only this for their object, labor uselessly. We know we are not dreaming, however powerless we are to prove it by reason. This inability demonstrates only the weakness of our reason, and not, as they claim, the uncertainty of all our knowledge.
For knowledge of first principles, such as space, time, motion, number, is as firm as any we derive from reasoning. Reason must use this knowledge from the heart and instinct, and base all its arguments on it...Principles are felt, propositions are proved; all with certainty, though in different ways. And it is as useless and absurd for reason to demand from the heart proofs of its first principles before accepting them, as it would be for the heart to demand from reason an intuition of all demonstrated propositions before receiving them.
This inability must serve, then, only to humble reason, which would want to be judge of everything, but not to attack our certainty. As if reason alone were capable of teaching us! Would to God, on the contrary, that we never had need of it, and that we knew everything by instinct and intuition. But nature has refused us this good. (Pensées, S142/L110, Roger Ariew translation, Hackett, [2005], 31)
