Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. It is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational argument. The word “philosophy” comes from the Greek ????????? (philosophia), which literally means “love of wisdom. Skepticism is a philosophical attitude that, in its most extreme form, questions the possibility of obtaining any sort of knowledge.
It was first articulated by Pyrrho, who believed that everything could be doubted except appearances. Sextus Empiricus (2nd century AD), skepticism’s most prominent advocate, describes it as an “ability to place in antithesis, in any manner whatever, appearances and judgments, and thus … to come first of all to a suspension of judgment and then to mental tranquility. ” Skepticism so conceived is not merely the use of doubt, but is the use of doubt for a particular end: a calmness of the soul, or ataraxia. Skepticism poses itself as a challenge to dogmatism, whose adherents think they have found the truth.
Sextus noted that the reliability of perception may always be questioned, because it is idiosyncratic to the perceiver. The appearance of individual things changes depending on whether they are in a group: for example, the shavings of a goat’s horn are white when taken alone, yet the intact horn is black. A pencil, when viewed lengthwise, looks like a stick; but when examined at the tip, it looks merely like a circle. Skepticism was revived in the early modern period by Michel de Montaigne and Blaise Pascal. Its most extreme exponent, however, was David Hume.
Hume argued that there are only two kinds of reasoning: what he called probable and demonstrative (cf. Hume’s fork). Neither of these two forms of reasoning can lead us to a reasonable belief in the continued existence of an external world. Demonstrative reasoning cannot do this, because demonstration (that is, deductive reasoning from well-founded premises) alone cannot establish the uniformity of nature (as captured by scientific laws and principles, for example). Such reason alone cannot establish that the future will resemble the past.
We have certain beliefs about the world (that the sun will rise tomorrow, for example), but these beliefs are the product of habit and custom, and do not depend on any sort of logical inferences from what is already given certain. But probable reasoning (inductive reasoning), which aims to take us from the observed to the unobserved, cannot do this either: it also depends on the uniformity of nature, and this supposed uniformity cannot be proved, without circularity, by any appeal to uniformity. The best that either sort of reasoning can accomplish is conditional truth: if certain assumptions are true, then certain conclusions follow.
So nothing about the world can be established with certainty. Hume concludes that there is no solution to the skeptical argument—except, in effect, to ignore it. Even if these matters were resolved in every case, we would have in turn to justify our standard of justification, leading to an infinite regress (hence the term regress skepticism). Many philosophers have questioned the value of such skeptical arguments. The question of whether we can achieve knowledge of the external world is based on how high a standard we set for the justification of such knowledge.
If our standard is absolute certainty, then we cannot progress beyond the existence of mental sensations. We cannot even deduce the existence of a coherent or continuing “I” that experiences these sensations, much less the existence of an external world. On the other hand, if our standard is too low, then we admit follies and illusions into our body of knowledge. This argument against absolute skepticism asserts that the practical philosopher must move beyond solipsism, and accept a standard for knowledge that is high but not absolute.