What is scepticism?
Scepticism comes from a Greek word meaning "to look carefully". A sceptic does not just say "nothing can be known". A sceptic asks: how do we know that we know?
The ancient sceptics (the school of Pyrrho, later Sextus Empiricus) collected short arguments called tropes, which means "ways" or "modes". Each trope shows a way in which a claim to knowledge can be doubted. We study two groups: tropes about perception and tropes about justification (giving reasons).
Relativity of perception
The same thing can look, feel or taste different to different people, or to the same person at different times.
- Three-bowl test: hold one hand in hot water and the other in cold. Then put both in warm water. The same water feels cold to one hand and hot to the other.
- Looks: two lines of equal length can look unequal if one has arrow tips pointing in and the other out. A coin looks round from the front and oval from the side. A far mountain looks small.
- Different living beings: honey is sweet to us, but may taste different to other animals.
The sceptic says: if how a thing appears depends on the condition of the one who senses it, then I know how it appears to me now, but not how it really is.
A fair reply: we can check appearances with other tools (a ruler, a thermometer, other people). The sceptic would ask whether those checks are free from doubt too.
Regress: the never-ending "Why?"
To know something, we need a reason (a justification). But a reason is also a claim, and it needs a reason, too.
This is the regress: claim ← reason 1 ← reason 2 ← reason 3 ← … If it never ends, then no claim is ever finally supported. We would need to give infinitely many reasons, and nobody can.
Circularity and arbitrariness
We have two other options, but they look bad too.
- Circularity: the chain returns to where it started. "The book is true because the writer is honest. The writer is honest because the book says so." Here the claim ends up holding itself up, so it proves nothing new.
- Arbitrariness (assumption): we stop at a reason and say "this needs no reason". But why stop here and not somewhere else? A stop with no reason looks like a choice made at random. Another person can stop somewhere else.
Together these three are often called the Agrippan trilemma (the "tri-lemma" means three bad choices). Sceptics used it to show that justification is hard.
What did sceptics want from this?
The Pyrrhonian sceptics did not want to win arguments. They tried to reach suspension of judgement (epoché): saying "I will not decide yes or no" when the arguments on both sides are equally strong. They claimed this brought calm (ataraxia).
Later thinkers gave answers: some said some beliefs need no further reason (basic beliefs), some said beliefs support each other like a web (coherence), and science adds tests to check our senses. The sceptical tropes are still the standard way to start a conversation about knowledge.
Try it
Try the three-bowl test at home with safe, lukewarm and cool water (never hot enough to hurt). Write down what each hand feels.
Then play the "Why?" game with a friend for one minute. Count how many answers you give before you reach "just because" (assumption), repeat yourself (circle), or give up (regress).
Key formulas and definitions
- Scepticism: asking "how do we know that we know?"
- Trope = a short standard argument (a "way") for doubt
- Relativity of perception: how a thing appears depends on who senses it and in what condition
- Justification chain: claim ← reason ← reason ← …
- Three endings: regress (never ends), circularity (goes round), arbitrariness (stops at an assumption)
- Suspension of judgement (epoché) → calm (ataraxia)
Worked examples
1. You say "This soup is hot." Your friend, who just ate ice cream, says "It is warm." Which trope is this?
Relativity of perception. How the soup feels depends on the condition of the person (your mouth had no cold food, theirs did). Both are telling how it appears to them, not a final truth about the soup.
2. Ravi says "The news channel is reliable because it says it is reliable." Which trope fits?
Circularity. The claim (the channel is reliable) is used to support itself. We need an outside reason, such as a record of checked facts.
3. A student keeps asking "Why?" about a rule, and the teacher finally says "Because that is the rule." Which trope?
Arbitrariness (an assumption). The chain stops at a reason with no reason behind it. The student can ask why it stopped there.
Common mistakes
- Thinking a sceptic says "nothing is true". Ancient sceptics suspended judgement instead of denying.
- Mixing up the three endings. Regress never ends, circularity returns to the start, arbitrariness stops with no reason.
- Saying the three-bowl test proves the water has no temperature. It only shows our hands are not perfect meters.
- Treating doubt as the same as laziness. Scepticism is careful looking, which asks for good reasons.