Debate the Skeptic

The Skeptic is a chatbot that plays an ancient skeptic. Tell it what you believe, and it argues until neither side is weightier. Then you suspend judgment, and tranquility follows. Allegedly.

You state a belief, and The Skeptic helps you map out why you believe it, one reason at a time, drawing your argument map as you go. Follow any line of reasoning far enough and it rests on a fundamental assumption, goes in a circle, or goes on forever. Once every line has run out, the suspension of judgment is yours, absolutely free.

Reaching the suspension of judgment is winning.

Debating the Skeptic teaches you about the structure of arguments, epistemology, and Pyrrhonian skepticism, all while bringing you to a state of tranquility.

I first built The Skeptic in 2007, as a philosophy grad student at Princeton: hundreds of hand-coded rules that mostly said "Yeah, but I believe that not-P. Justify yourself!" until you gave up. There was no vibe coding back then, so it was intense, grueling labor and the results were mixed.

In 2026, I revived it with AI, and now I am finally tranquil.

The Skeptic is Sextus Empiricus, brought back to life by AI (Claude, by Anthropic). Its studies, surveys, conferences, and Rutgers philosophers are made up.

These are the house rules, not a limitation of skepticism. No medical advice, nothing dangerous, no hate, no atrocity denial. The aim is to attain tranquility.

Yes, and real people might read them for quality assurance and entertainment. Feel free to use a fake name and don’t share anything private. If you request an invitation, the email you enter is kept so the Skeptic’s handler can get back to you.

It doesn't. Support it by reading my work, and then debating it. Or let me know if you want to help support The Skeptic so that it can be made more widely available.

You’ve probably hit an hourly or daily limit, or the Skeptic is resting after a busy day. Come back when advised, or request an invitation for your own tranquility allowance.

You probably hit a usage limit. The Skeptic costs real life money to run and is currently unfunded, so, following the customs of our culture, there are limits on how much it can be used. If you're interested in supporting or hosting The Skeptic so that we can remove these limits and make it more widely available, please let me know.

The practice of setting opposing considerations against each other until neither is more convincing (PH I.8–10), resulting in the suspension of judgment, from which tranquility follows “as a shadow follows a body” (PH I.29).

No. When the Skeptic tells you that honey tastes bitter to someone with a fever or that a paper in the Journal of Applied Astrology holds the opposite view, it isn't arguing that you're wrong. It's setting a consideration against your belief to show that the question of whether your belief is true is open, and hence that your belief can't simply be taken for granted—it needs justification.

Because showing that the other side is wrong doesn't show that yours is right. The Skeptic wants to help you examine your reasons for holding your beliefs, not your reasons for rejecting others. Once you see that your justification cannot be sustained, you suspend judgment and become tranquil at last.

That's a claim too. Skeptics suspend judgment about it.

Honey appears sweet to them, too; they just suspend judgment on whether it is sweet (PH I.19–20). They live by appearances, nature, feelings, customs, and know-how (PH I.23–24).

The Skeptic does not dispute claims about appearances or definitions, but such claims do not support claims about how things are beyond appearances. Definitions are empty and only constrain how certain states of affairs are described, and appearances don't suggest anything about how things are beyond the appearances without the help of further premises, which the Skeptic does dispute.

Sometimes a reason rests on what a word means. A definition, for Sextus, settles how we’re using our words, not how things are. So, the Skeptic treats claims that are true by definition as empty.

For example, one might claim that faith is, by definition, arational. The Skeptic doesn’t quarrel over the meanings of words. Instead, the Skeptic asks what is meant by the word and then uses the supplied definition to interpret any affected claims. For example, if we define faith as arational belief, then the belief that faith does not require rationality amounts to the claim that arational belief does not require rationality. This, the Skeptic does not dispute; it is trivial. But the Skeptic points out that this empty claim tells us nothing about the world. A substantive question remains, that of whether the thing people ordinarily call faith, whatever that thing is, requires rationality. The definition has not made progress on settling that question.

Sextus Empiricus devotes a chapter of Outlines of Pyrrhonism to definitions (II.205–212). The dogmatists took them to be tools of knowledge, but Sextus argues that if you don’t already know what’s being defined, the definition can’t teach it to you, and if you do, the definition adds nothing. And if every term had to be defined before it could be used, the definitions would go on forever.

Skeptical claims work like laxatives, flushing themselves out along with everything else (PH I.206).

Ready-made arguments for suspending judgment. Some favorites to try on your friends:

• Disagreement: You say P; others say not-P. Who decides?
• Relativity: Honey tastes sweet to you, bitter to someone with a fever.
• Distance: The square tower looks round from far away.
• Regress: What supports that? And that? And that?
• Hypothesis: If you can just assume P, I can just assume not-P.
• Circularity: If P rests on Q and Q rests on P, nothing holds either one up.

Sextus collects them in sets: the Ten Modes of Aenesidemus, the Five Modes of Agrippa, and a few more (PH I.36–186).

• Pyrrho (c. 360–270 BCE): the founder. Wrote nothing. Friends kept him from walking off cliffs.
• Timon: his student, who mocked other philosophers in verse.
• Aenesidemus and Agrippa: traditionally credited with the Ten Modes and the Five Modes, respectively.
• Sextus Empiricus (c. 200 CE): a doctor, and our main source.

• Sextus Empiricus, Outlines of Scepticism, trans. Annas and Barnes. Start here.
• Mates, The Skeptic Way. Another translation, with commentary.
• Sextus Empiricus, How to Keep an Open Mind: An Ancient Guide to Thinking Like a Skeptic, trans. Bett. A short selection for general readers, with the Greek facing.
• Annas and Barnes, The Modes of Scepticism.
• Barnes, The Toils of Scepticism.
• Hankinson, The Sceptics.
• Bett (ed.), The Cambridge Companion to Ancient Scepticism.
• The Stanford Encyclopedia of Philosophy on Ancient Skepticism and Sextus Empiricus. Free and accurate (or maybe it isn't—who knows?).

• Joe Lau and Jonathan Chan, Critical Thinking Web: Argument Analysis. Free online tutorials, including argument mapping and hidden assumptions, the skills the Skeptic puts to work.
• Twardy, Argument Maps Improve Critical Thinking, Teaching Philosophy (2004).
• Harrell, Argument Diagramming and Critical Thinking in Introductory Philosophy, Higher Education Research & Development (2011).
• van Gelder, Using Argument Mapping to Improve Critical Thinking Skills, in The Palgrave Handbook of Critical Thinking in Higher Education (2015).