Podcast brief

Cicero, Carneades, and Skeptical Probability

Massimo Pigliucci joins Caleb Ontiveros to trace ancient skepticism from Pyrrho through Carneades to Cicero and its bearing on certainty and polarization today.

A Stoa brief of an episode from Stoa Conversations

Why You Should Be A Skeptic With Massimo Pigliucci (Episode 228)

With Massimo Pigliucci Published June 23, 2026 58 min

Listen to the original episode

The episode belongs to its makers. This page summarizes its arguments in Stoa's words and points to the moments where they are made. Brief updated September 27, 2026.

The brief

Massimo Pigliucci argues that ancient skepticism, especially the Academic tradition running through Carneades to Cicero, offers a workable alternative to both dogmatism and paralysis. Speaking with Caleb Ontiveros, he distinguishes this from Pyrrhonism, which counsels suspending judgment on any non-evident question to reach tranquility, letting custom and expert testimony guide everyday life. Pigliucci suggests this path forecloses too much: it risks passive acceptance of unjust customs and leaves little room for science, philosophy, or ethics to develop.

The Academic skeptics take a different route, one Pigliucci traces back to Socrates' admission of ignorance and his habit of testing others' false confidence. That practice matured into fallibilism, the view that both senses and reason can err. Carneades then added a further move: instead of just admitting fallibility, we can grade how convincing a belief is, from barely plausible to thoroughly tested against everything else we know. Cicero's Latin rendering of Carneades' term for this, probabilis, is the root of the modern word probability. The result is a framework for acting without certainty, weighing degrees of confidence against what is at stake.

This bears on the long Stoic-skeptic dispute over the cataleptic impression, the Stoic claim that certain impressions carry an unmistakable mark of truth. Pigliucci notes the schools converged over time: Stoics conceded such impressions are rare even for the sage, while skeptics granted some impressions deserve very high confidence. He extends the point to modern polarization, arguing that treating one's own view as certain rather than as a fallible best guess is what lets people write off opponents as evil or stupid rather than simply mistaken.

The conversation also surveys Cicero's own works, including On Divination as an early critique of pseudoscience and On Ends as a fair-minded tour of rival philosophies ending in open questions. Pigliucci presents Cicero's break with Stoic self-sufficiency on friendship, valuing it as a genuine good rather than merely preferred, and closes with Cicero's death at the hands of Mark Antony's soldiers as philosophy enacted in a life spent trying to be useful to others.

Strongest arguments

Pyrrhonism counsels universal suspension of judgment

2:48

Pigliucci explains that the Pyrrhonists held that on complex questions like the existence of God or the nature of the good life, we should suspend judgment because arguments on both sides seem equally strong, aiming at tranquility while relying on custom and expert testimony for everyday matters. He argues this forecloses science, philosophy, and ethics, and risks passive acceptance of unjust customs such as slavery.

Academic skeptics developed fallibilism from Socratic inquiry

6:38

Pigliucci traces the Academic skeptics back to Socrates' claim to know nothing and his method of exposing others' false confidence, often ending in open questions. Over time this developed into fallibilism, the view that both the senses and reason are unreliable sources of knowledge, so any belief should be held only tentatively.

Carneades introduced graded degrees of probability

10:20

Carneades proposed that instead of merely admitting fallibility, we can assess how likely a belief is to be true, ranging from barely convincing to thoroughly investigated and consistent with everything else known. Cicero translated the Greek term for this as probabilis, the root of the modern concept of probability. The upshot is that we do not need certainty to act, only an assessment of likelihood weighed against what is at stake.

Stoics and skeptics debated the cataleptic impression

18:00

The Stoics held that certain impressions carry an unmistakable mark of truth that the ideal sage could always recognize. The skeptics denied any such mark exists in raw sense data, arguing that interpretation always involves a mind that can err even in seemingly obvious cases. Pigliucci notes the two schools converged over time, since Stoics conceded the sage rarely encounters a genuine cataleptic impression, while skeptics granted some impressions warrant very high confidence.

Certainty fuels polarization; fallibilism offers a healthier attitude

22:20

Pigliucci argues that treating one's own view as certainly true, rather than as a fallible best guess, is what allows people to conclude that those who disagree are not just wrong but evil or stupid. Adopting fallibilism does not require changing one's conclusions, but it changes the attitude one holds them with, making a person open to correction rather than defensive.

Cicero combines Academic skepticism with sympathy for Stoic ethics

25:30

Cicero considered himself an Academic skeptic but wrote favorably on Stoic ethics, for instance in On Duties, while criticizing Stoic commitments he found wrong, such as divination in On Divination. Pigliucci presents this as the advantage of the skeptical approach: one can adopt what seems right from any school without dogmatic commitment to all of it.

Cicero departs from Stoic self-sufficiency on friendship

38:35

Pigliucci presents Cicero's view that friendship is a genuine good, not merely a preferred indifferent, arguing through a thought experiment that most people would rather have less with friends than have every material good alone on a deserted island. This is contrasted with the Stoic position that the sage is self-sufficient even without friends, and with the Epicurean view that friendship is valued mainly instrumentally for the pleasure it brings.

Disagreements

Whether virtue is the only good or one good among several

37:20

The Stoics hold virtue is the only good, with everything else classed as indifferent. Cicero, as presented by Pigliucci, leans strongly toward valuing virtue but is not convinced it is the sole good, giving friendship independent weight as a good in itself.

Whether any impression can bear an unmistakable mark of truth

18:00

The Stoics maintained that a cataleptic impression carries a mark of truth that, at least for the sage, cannot be mistaken. The skeptics denied that the world provides any such mark, holding that all data must be interpreted by a fallible mind and so no impression is immune from possible error.

Concepts discussed

Skepticism The philosophical position that we should suspend judgment because certainty about the external world, or about the correspondence of our ideas to it, cannot be established.

Philosophers and works discussed

Cicero
Carneades
On Divination By Cicero.
On Ends By Cicero.

Questions this episode answers

What is the difference between Pyrrhonism and Academic skepticism?
1:40

Pyrrhonism counsels suspending judgment on all non-evident questions to reach tranquility, following custom and experts for everyday matters. Academic skepticism traces back to Socratic inquiry and developed into fallibilism, the view that senses and reason can err, which permits graded confidence rather than total suspension.
How did Carneades develop the idea of probability in ancient skepticism?
10:20

Carneades argued that instead of only admitting fallibility, we can grade how convincing a belief is, from barely plausible up to thoroughly investigated, and act according to that degree of confidence weighed against what is at stake. Cicero translated his term for this as probabilis, the origin of the modern word probability.
What is the Stoic doctrine of the cataleptic impression and why did skeptics reject it?
18:00

The Stoics held that certain impressions grab the mind with an unmistakable mark of truth that the sage can always recognize. The skeptics rejected this, arguing the world provides raw data without any built-in mark of truth, so any impression can in principle be mistaken.
Why did Cicero write On Divination against the Stoics?
27:00

Cicero wrote On Divination to systematically debunk astrology and divination, practices the Stoics defended based on their view of a cosmic web of cause and effect. Pigliucci calls it an early book against pseudoscience, noting Cicero's example that Roman soldiers who died at Cannae did not share the same horoscope.
How does Cicero's view of friendship differ from the Stoic and Epicurean views?
38:35

Cicero argues friendship is a genuine good in itself, illustrated by his claim he would rather have less with friends than all material goods alone. This contrasts with the Stoic view that the sage is self-sufficient even without friends, and the Epicurean view that friendship is valued mainly as a source of pleasure.
Why does excessive certainty contribute to political polarization?
22:20

Pigliucci argues that concluding an opposing side is not just wrong but evil or stupid requires a very high degree of confidence in one's own correctness. A fallibilist attitude, admitting one might be wrong, keeps the same conclusions but changes the stance toward others to one open to correction.

Related primary passages

Some things are in our control and others not. Things in our control are opinion, pursuit, desire, aversion, and, in a word, whatever are our own actions. Things not in our control are body, property, reputation, command, and, in one word, whatever are not our own actions.

Epictetus, Handbook 1 Read in context

This is the founding statement of the dichotomy of control, the axis the rest of Epictetus's teaching turns on.

Sources

Epictetus, Handbook Primary text, Stoa library
Stoa Conversations, Why You Should Be A Skeptic With Massimo Pigliucci (Episode 228) Podcast episode, original episode