---
title: "Philosophical skepticism"
chunk: 4/9
source: "https://en.wikipedia.org/wiki/Philosophical_skepticism"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:37:00.045187+00:00"
instance: "kb-cron"
---

===== Sextus Empiricus =====

The works of Sextus Empiricus (c. 200 CE) are the main surviving account of ancient Pyrrhonism. Long before Sextus's time, the Academy had abandoned skepticism and had been destroyed as a formal institution. Sextus compiled and further developed the Pyrrhonists' skeptical arguments, most of which were directed against the Stoics but included arguments against all of the schools of Hellenistic philosophy, including the Academic skeptics.
Sextus, as the most systematic author of the works by Hellenistic skeptics which have survived,  noted that there are at least ten modes of skepticism. These modes may be broken down into three categories: one may be skeptical of the subjective perceiver, of the objective world, and the relation between perceiver and the world. His arguments are as follows.
Subjectively, the powers of the senses and reasoning may vary among different people. And since knowledge is a product of one or the other, and since neither are reliable, knowledge would seem to be in trouble. For instance, a color-blind person sees the world quite differently from everyone else. Moreover, one cannot even give preference based on the power of reason, i.e., by treating the rational animal as a carrier of greater knowledge than the irrational animal, since the irrational animal is still adept at navigating their environment, which suggests the ability to "know" about some aspects of the environment.
Secondly, the personality of the individual might also influence what they observe, since (it is argued) preferences are based on sense-impressions, differences in preferences can be attributed to differences in the way that people are affected by the object. (Empiricus: 56)
Third, the perceptions of each individual sense seemingly have nothing in common with the other senses: i.e., the color "red" has little to do with the feeling of touching a red object. This is manifest when our senses "disagree" with each other: for example, a mirage presents certain visible features, but is not responsive to any other kind of sense. In that case, our other senses defeat the impressions of sight. But one may also be lacking enough powers of sense to understand the world in its entirety: if one had an extra sense, then one might know of things in a way that the present five senses are unable to advise us of. Given that our senses can be shown to be unreliable by appealing to other senses, and so our senses may be incomplete (relative to some more perfect sense that one lacks), then it follows that all of our senses may be unreliable. (Empiricus: 58)
Fourth, our circumstances when one perceives anything may be either natural or unnatural, i.e., one may be either in a state of wakefulness or sleep. But it is entirely possible that things in the world really are exactly as they appear to be to those in unnatural states (i.e., if everything were an elaborate dream). (Empiricus: 59)
One can have reasons for doubt that are based on the relationship between objective "facts" and subjective experience. The positions, distances, and places of objects would seem to affect how they are perceived by the person: for instance, the portico may appear tapered when viewed from one end, but symmetrical when viewed at the other; and these features are different. Because they are different features, to believe the object has both properties at the same time is to believe it has two contradictory properties. Since this is absurd, one must suspend judgment about what properties it possesses due to the contradictory experiences. (Empiricus: 63)
One may also observe that the things one perceives are, in a sense, polluted by experience. Any given perception—say, of a chair—will always be perceived within some context or other (i.e., next to a table, on a mat, etc.) Since this is the case, one often only speaks of ideas as they occur in the context of the other things that are paired with it, and therefore, one can never know of the true nature of the thing, but only how it appears to us in context. (Empiricus: 64)
Along the same lines, the skeptic may insist that all things are relative, by arguing that:

Absolute appearances either differ from relative appearances, or they do not.
If absolutes do not differ from relatives, then they are themselves relative.
But if absolutes do differ from relatives, then they are relative, because all things that differ must differ from something; and to "differ" from something is to be relative to something. (Empiricus: 67)
Finally, one has reason to disbelieve that one knows anything by looking at problems in understanding objects by themselves. Things, when taken individually, may appear to be very different from when they are in mass quantities: for instance, the shavings of a goat's horn are white when taken alone, yet the horn intact is black. 

===== Skeptical arguments =====
The ancient Greek Pyrrhonists developed sets of arguments to demonstrate that claims about reality cannot be adequately justified. Two sets of these arguments are well known. The oldest set is known as the ten tropes of Aenesidemus—although whether he invented the tropes or just systematized them from prior Pyrrhonist works is unknown. The tropes represent reasons for epoché (suspension of judgment). These are as follows:

Different animals manifest different modes of perception;
Similar differences are seen among individual men;
For the same man, information perceived with the senses is self-contradictory
Furthermore, it varies from time to time with physical changes
In addition, this data differs according to local relations
Objects are known only indirectly through the medium of air, moisture, etc.
These objects are in a condition of perpetual change in color, temperature, size and motion
All perceptions are relative and interact one upon another
Our impressions become less critical through repetition and custom
All men are brought up with different beliefs, under different laws and social conditions
Another set are known as the five tropes of Agrippa: