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Philosophy Then

Don’t Be So Sure

Peter Adamson on skepticism in the history of philosophy.

You may think you know what philosophical skepticism is. It’s commonly traced back to René Descartes, who in his Meditations (1642) asks whether there is anything of which he can be completely certain. Famously, he decides there is: he cannot doubt his own existence. But first he entertains radical skeptical scenarios, notably that he’s dreaming, or that an ‘evil demon’ may be inducing in him false beliefs that seem certain. Pop culture embraces this form of skepticism most famously in the Wachowskis’ film The Matrix (1999), which suggests that you may be a brain in a vat, or rather, Keanu Reeves in a vat. Cartesian skepticism sets a rigorous test for our beliefs, in the hope of finding at least some beliefs that can survive the challenge.

But don’t be so sure about this picture. For one thing, this kind of skepticism appears before Descartes. It is found for instance in the fourteenth century thinker Nicholas of Autrecourt, who wanted to challenge the Aristotelian scholasticism of his day. He proposed that absolute certainty is possible, but only about a very limited range of things. The paradigm case of certainty would be the principle of non-contradiction, which says that a proposition and its precise denial cannot both be true. Nicholas inferred that all genuine knowledge would have to meet this standard of certainty. Thus, the only things you can know for sure are those whose falsehood would entail a contradiction. For instance, you can know that squares have four sides and that a human is an animal, since these things are true by definition; but you cannot know for sure that any square or human you are seeing is real, since no contradiction ensues from supposing them to be illusions. Nicholas ultimately concluded that for the most part, the best we can do is to find beliefs that are probable, not certain.

For another thing, there were still earlier forms of skepticism that were very different. The greatest classical Greek skeptic, Sextus Empiricus, lived in the second century AD. He would have seen Nicholas’ admission of the ‘probable’ as a divergence from genuine skepticism, which for him involves ‘suspending judgment’ about all beliefs. His approach is to pile up arguments on both sides of every disputed question, showing that the arguments in favor are ‘in balance’ with those against. Yet Sextus never asserts that any issue is irresolvable or guaranteed to remain uncertain, because he wants to avoid falling into the contradiction of claiming to be certain that nothing is certain. Indeed he critiques other so-called ‘skeptics’ for claiming they know that nothing can be known. They come no closer to true skepticism than do the Stoics. Whereas the Stoics ‘dogmatically’ asserted positive teachings – for instance that virtue is good or that God exists and exercises providence – these other skeptics ‘dogmatically’ asserted a negative teaching, namely that knowledge is impossible.

In the same century, a third kind of skepticism was being pursued in India by the Buddhist Nagarjuna. He was out to deny the ‘intrinsic reality’ (‘svabhava’) of things, by showing that nothing has any independent nature. In a series of brilliant arguments, he shows that such phenomena as causation, motion, and perception involve internal contradictions. For instance, causation must involve either a thing causing itself; or it being caused by another thing; or it being caused both by itself and another thing; or it arising with no cause at all – but all these options, he argues, are absurd.

The purpose of Nagarjuna’s philosophical project is debated by scholars. Some think that he’s critiquing philosophical pretensions to expose the reality that underlies conventional experience and language, like an ancient Buddhist Wittgenstein. Others suppose that he goes so far as to deny the principle of non-contradiction and urges us to embrace mysticism. Whatever the case, it seems clear that Sextus would convict Nagarjuna of being a negative dogmatist.

This diversity means that no one response will be effective against all skeptics. Against Nicholas, Descartes, and the Wachowskis, one might urge that they are simply being too demanding: knowledge does not require that we rule out all possibility of falsehood, so that only self-certifying truths can be known. Your everyday experiences do give you knowledge, because in fact you are neither being deceived by an evil demon nor are plugged into a computer simulation – even if you cannot prove it beyond all shadow of doubt. But this would not work against Sextus or Nagarjuna, because neither of them try to induce skepticism using such radical skeptical scenarios. Sextus does so rather by showing you that all your beliefs are open to controversy and that the arguments on both sides of each controversy are in balance; Nagarjuna by offering a critique of the concepts you previously took for granted.

For all their diversity, these forms of skepticism do have one thing in common: all emerged as responses to what Sextus would call ‘dogmatic’ opponents. Skepticism is typically reactive, and often uses the tools of its opponents for its own purposes. The notion of ‘suspending judgment’ was at home in Stoicism, because the Stoics argued that a perfect sage could avoid falling into error by suspending judgment whenever sufficient evidence was lacking. (A famous story has a Stoic biting into a fake piece of fruit, and excusing himself on the grounds that he did not form the belief that it was fruit, but the belief that it looked like fruit.) Nicholas was likewise offering a critique of contemporary Aristotelians, granting their principle of non-contradiction but then pointing out that none of their other doctrines were on a par with this foundational idea. Nagarjuna was attacking thinkers in the Vedic tradition, but also fellow Buddhists, all of whom operated with the notion of svabhava that he sought to undermine. The skeptical game, it would seem, is best played against an opponent.

Peter Adamson is the author of A History of Philosophy Without Any Gaps, Vols 1, 2 & 3, available from OUP. They’re based on his popular History of Philosophy podcast.