Against the Logicians (Adversus Mathematicos VII–VIII)

The central argument is that no criterion of truth can be established. Sextus examines the three main candidates—the human being as criterion, the senses as criterion, and reason as criterion—and shows that each generates equipollent arguments for and against, producing suspension. The criterion is the pivot of dogmatic epistemology: if we had a reliable criterion, we could distinguish true from false impressions and ground knowledge. Sextus's strategy is to show that any proposed criterion must itself be judged by a criterion, leading to infinite regress; or it must be assumed without justification, which is arbitrary; or it must be validated by itself, which is circular. These are the Agrippan modes, and Against the Logicians is their most extensive application to the theory of knowledge.

Against the Logicians is the fuller, more detailed treatment of the same material that appears in compressed form in Outlines Book II. Sextus refers to his own works in ways that indicate Against the Logicians is the more extensive version . The Outlines is the systematic overview, designed to present the whole of skepticism; Against the Logicians is a sustained polemic against a specific dogmatic tradition. Readers new to Sextus should begin with the Outlines, which provides the framework and vocabulary. Those who want to see the skeptical method applied in exhaustive detail to the Stoic theory of knowledge should turn to Against the Logicians. The two works are complementary, not redundant.

The Stoics held that some impressions are 'apprehensive' (kataleptic)—so clear and distinct that they compel assent and guarantee truth. Sextus attacks this doctrine by arguing that no impression carries a mark that infallibly distinguishes it from a false one. The Academic skeptic Carneades had already argued that no impression is infallible, but he allowed that some are persuasive. Sextus goes further: even the persuasive character of an impression cannot be known to correspond to reality, because we have no independent access to reality to check it. The distinction is central because it shows that the Stoic criterion presupposes what it claims to establish—a reliable mark of truth that is itself reliable.

Bury's Loeb edition (1935) was the standard English translation for decades, with facing Greek text . Bett's Cambridge edition (2005) is the first new English translation since Bury and is more philosophically precise. Bett translates technical terms literally to preserve their connections to ordinary Greek usage, and his introduction and notes engage with contemporary epistemological debates. For scholarly work, Bett's edition is now the standard; Bury's remains useful for its Greek text and its historical importance. Readers should be aware that the two translations differ in significant ways, particularly in the rendering of technical vocabulary, and that Bett's edition includes a glossary and extensive explanatory notes that Bury's lacks.

The Agrippan modes that Sextus deploys are the ancestor of the regress problem that continues to structure contemporary epistemology. The problem of the criterion—how do we know which criterion of truth is correct?—remains unresolved, and Sextus's formulation of it is still cited in debates between foundationalists, coherentists, and infinitists. Richard Bett notes that the Pyrrhonian argumentative arsenal poses a serious epistemological challenge for present-day analytic philosophers, as it did for early modern thinkers . Sextus's critique of the Stoic theory of knowledge anticipates modern discussions of epistemic justification, and his distinction between appearance and reality remains central to skeptical arguments. Reading Against the Logicians is thus not merely historical; it is an encounter with a live philosophical challenge.

Its influence in antiquity is difficult to trace directly, but the skeptical tradition it represents was a major force in Hellenistic philosophy. The work was known to later skeptics and was part of the corpus that informed the revival of Pyrrhonism in the sixteenth century. When Sextus's works were rediscovered and translated in the 1560s, Against the Logicians contributed to the 'Pyrrhonian crisis' that shaped early modern philosophy. Its arguments were absorbed into the skeptical currents that fed Descartes, Hume, and others. The work is thus a crucial link in the transmission of ancient skepticism to the modern world, even if its direct influence is often mediated by the Outlines.