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Article abstract: Promoting Pyrrhonian radical Skepticism, Sextus compiled arguments against dogmatic philosophers of Stoicism, Epicureanism, and Academic Skepticism, and in doing so he laid the foundation for modern philosophy.

Early Life

Little is known about Sextus Empiricus. He was an obscure Hellenistic writer but the only Greek Pyrrhonian Skeptic whose works survived and eventually made a great impact on Western intellectual history. He is said to be the last of the Alexandrian radical Pyrrhonist leaders.

Life’s Work

Experts speculate that Sextus was a physician by profession. He refers to Asclepias as the founder of “our science” (medicine), and Diogenes Laërtius and Galen, personal physician to several Roman emperors in the first and second centuries c.e., mention that he belonged to the Empirical school of medicine. Sextus was also a philosophy teacher and a kind of therapist advocating mental tranquillity through suspension of judgment.

Sextus was not an original philosopher but an excellent and methodical expounder and compiler of Pyrrhonist arguments handed down to him by his teacher Herodotus and other Skeptics. Being a physician and, in the modern sense, a scientist perhaps gave him a natural talent for meticulous compilation and classification of arguments.

Sextus was part of a radical movement, the Alexandrian Pyrrhonists, which believed in returning to traditional Pyrrhonian principles and engaging in relentless struggle against certain dogmatic philosophical ideas. One of the major goals of the group was to construct arguments against any kind of dogmatism, particularly Stoicism, Epicureanism, and the Academic Skepticism prevalent in Plato’s Academy. Sextus argued against Academic Skepticism and its famous teachers, Arcesilaus and Carneades. Pyrrhonian Skeptics considered the Academic Skeptics dogmatic philosophers for taking the position that nothing is knowable. Sextus argued that we are not allowed even this much knowledge; the best course is to suspend judgment.

Sextus was an ardent follower of Pyrrho of Elis, sometimes called the founder of Skepticism. It is said that Pyrrho, through strict observance of Skeptical practices, achieved an extraordinary tranquillity and indifference. Like Socrates, Pyrrho did not write down his thoughts and lectures. What is known about Pyrrho comes from surviving fragments written in poems by one of his devoted pupils, Timon of Philius, in the third century b.c.e. Sextus attempted to capture Pyrrho’s basic teachings and compiled a massive collection of varied arguments against philosophers and professionals of all sorts, much as Plato did for Socrates.

Pyrrho and later Sextus did not establish a school of thought and were not interested in institutionalizing their philosophy, as Plato and Aristotle had been. Pyrrho’s, and indeed Sextus’s, philosophical method was to attack other philosophers and dogmatists. Pyrrho’s basic Skeptical attitude, according to Sextus, was that objects in the world are indifferent and unfathomable, and we cannot determine them because our senses and judgments are indifferent—they are neither true nor false. We should suspend judgment on everything. If we do so, we will achieve tranquillity in life.

Skepticism began to change from Academic to Pyrrhonist with the teachings of Aenesidemus in Alexandria as early as the first century. Aenesidemus had been a student at the Academy and was disenchanted with its radical Skeptics. Sextus contends that Aenesidemus’s policy of “determining nothing” resulted in happiness and Pyrrhonian tranquillity.

Pyrrhonism developed mainly among medical doctors in Alexandria, with Sextus as one of the movement’s leaders. Two of Sextus’s works survive in nearly complete form: Outlines of Pyrrhonism and Against the Mathematicians. In these books, Sextus describes Skepticism as the mental attitude that opposes the sources of certainty: appearances, objects of sense experience, and judgments people make about them. Through detailed and varied arguments, he shows that any dogmatic construction of knowledge only results in philosophical paradox and the illusion of knowledge. His books are rich sources of information about the ancient Greek philosophies.

The Outlines of Pyrrhonism is a methodical summary of Pyrrhonist Skeptical philosophy. It also compares the Skepticism of Pyrrho with that of the Academic Skeptics and attempts to show the weaknesses of the latter and the superiority of the former. The work is divided into three books. The first gives a general description of Pyrrhonist Skepticism and its terminology. The second and third present arguments against the basic premises of each of the divisions of philosophy: ethics, logic, and natural philosophy. Sextus’s arguments in this work and Against the Mathematicians are targeted mainly against three schools of “dogmatist” philosophers—Epicureans, Stoics, and Academic Skeptics—who believed they have knowledge of something.

Against the Mathematicians is divided into two major parts, “Against Professors of Liberal Studies” and “Against Dogmatists,” with eleven books in all. Sextus complies a detailed and meticulous taxonomy of arguments against many “dogmatist” philosophers, including the latter-day Aristoteleans and professionals and technicians such as medical doctors, military tacticians, musicians, astrologers, arithmeticians, geometricians, rhetoricians, and grammarians.

Like his Pyrrhonian predecessors, Sextus does not have an explicit set of beliefs or views of how the world is or ought to be. Instead, his objectives are to deconstruct the arguments of others within the system from which they have arisen. This is a more radical and controversial form of Skepticism than the Academics offered. At the end of Outlines of Pyrrhonism, Sextus claims that his arguments are mere pragmatic devices; they have no inherent value or superiority over any other arguments.

Sextus criticized Academic Skeptics as too dogmatic. Even the statement made by the Academics that nothing is knowable is itself a dogmatic claim of knowledge. This leads the Academic Skeptic into an irresolvable paradox—making an absolutist argument to support a relativist claim.

One of the most paradoxical claims, according to Sextus in his Outlines of Pyrrhonism, is the Academic Skeptics’ claim about truth. According to the Academic Skeptics, to decide any dispute about truth, the accepted criterion must be spelled out. However, discovery of the criterion becomes “impracticable” because a criterion cannot be adopted without adopting a criterion for that criterion, creating a hopeless regression ad infinitum. Sextus claims that this kind of circular reasoning afflicts any claim of truth, be it mathematical, empirical, religious, aesthetic, or ethical. In opposition to dogmatists, he announces that humanity is not the measure of truth.

What is important to recognize about Sextus’s version of Skepticism is that he does not state that there is or is not such a thing as truth. He merely suggests that we do not know. All we can do is to forgo making judgment one way or the other. He takes pains to explain this point and separates himself from the Academic Skeptics who claim they know with certainty that there is no truth. Sextus considered their view paradoxically dogmatic and against the spirit of Pyrrhonian Skepticism.

Sextus describes ten arguments, or “tropes,” developed by Aenesidemus for suspending judgment. All deal with the paradoxical nature of ascertaining whether our sense experiences belong to real objects existing in the external world or to our perceptions alone. He distinguishes between what modern philosophers of mind such as Daniel Dennett call “qualia,” the perceptions of sensory experiences, such as the redness of a tomato, and the external or physical attributions, such as light waves and chemical nature. Sextus claims that neither phenomenon is trustworthy. The same object may affect different people in different ways in different contexts.

Sextus believed that if Pyrrhonian Skepticism were adopted as a way of life, it would cure people of dogmatism, give them humility, and prepare them for a life of tranquillity. He says in Outlines of Pyrrhonism that Pyrrhonists like himself love humanity and want to save people from suffering and self-destruction caused by humankind’s “rashness” and “self-deception,” maladies of dogmatic living. People who need the Pyrrhonist cure, according to Sextus, are of two kinds: those who believe they have found the truth, such as Aristotelians and Epicureans, and those, such as Academic Skeptics, who believe they will never find it.

Sextus contends that various dogmatic schools of Hellenistic philosophy—the Stoic, Epicurean, and Academic—are all looking for “peace of mind” and that their theories of knowledge and truth are intended to lead to such “quietude.” Dogmatists, however, never achieve peace because they worry about whether their theories are true. The Skeptics have no such worries because they suspend judgment about knowledge and truth. The suspension of judgment, according to Sextus, produces calm indifference. In turn, this state of mind produces the tranquillity that the dogmatist seeks in vain.


It has been said that modern philosophy began with the historical accident of rediscovery of Sextus’s books in the fifteenth and sixteenth centuries. It changed Western intellectual development forever. However, Sextus’s writings had minimal influence on his contemporaries, and he was almost completely unknown in the Middle Ages. Only a handful of scholars had read his works before the first publication of his books in 1562 in France.

The first serious attempt to use Sextus’s books as major philosophical texts was made by Michel Eyquem de Montaigne, who established his own unique genre of skepticism inspired by Sextus.

Montaigne had much to do with the popularization of Sextus’s works, which resulted in new translations in Italian, French, and English appearing in the sixteenth and seventeenth centuries. The new Pyrrhonism of Montaigne and his disciples, addressing the intellectual, scientific, and theological crises of their time, led to nouveaux Pyrrhoniens as the intellectual avant-garde of Europe. By the seventeenth century, Sextus had been metamorphosed into the “divine Sextus” and was regarded as the father of modern philosophy. The effect of his thoughts about the problem of the criterion of truth stimulated a quest for certainty that gave rise to the new rationalism of René Descartes and the “constructive skepticism” of Pierre Gassendi and Marin Mersenne.

The first detailed explication of Sextus’s views was written in 1520 by Giovanni Pico della Mirandola, who used the philosopher’s books to demolish rational philosophy. His argument, however, was not that one should hold a radical doubt in everything, but rather that one would turn to humanity’s only guide in this “vale of tears,” the Christian Revelation. Thus, Pico della Mirandola, using Sextus’s arguments, established a kind of Christian Pyrrhonism that led to its later, more popular transformation propagated by Montaigne and his followers.

Theologians used Sextus’s arguments to combat skepticism’s corrosive influence on Christianity. Sextus’s works provided material for varied interests in the Renaissance and Reformation eras. Thinkers such as Montaigne, Mersenne, Gassendi, and Francisco Sanches turned to Sextus for inspiration in dealing with various intellectual crises.

The rediscovery of Sextus stimulated great works for and against Skepticism. For example, Descartes in his meditations used skeptical devices to reach his certainty of cogito, ergo sum (“I think, therefore I am”). On that foundation, he climbed back to the claims of the existence of the external world, God, and even Christianity. On the other hand, Scottish philosopher David Hume’s ingenious radical skepticism attempted to abolish any and all foundations for religion, morality, and the notion of physical causation. George Berkeley’s solipsism denied all external or physical existence in favor of an entirely mental world of existence. Sextus’s influence is felt even in 1970’s and 1980’s postmodern philosophies such as Jacques Derrida’s deconstructionism.

Sextus has been both admired and reviled. During his lifetime, he was accused of implicit dogmatism himself. In response, Sextus said that what he advocates has only the appearance of truth to him and that no one should take that as a dogmatic assertion of truth. However, there are still many unresolved problems and paradoxes in Sextus’s varied arguments. For example, the claim that one has to suspend judgment about everything turns out to be circular, for the statement itself becomes subject to suspension of judgment. On close examination, Sextus’s answers to this paradox are not satisfactory. Neither are rationalists’ responses to Sextus’s ingenious skeptical arguments, which will continue to capture people’s intellectual imagination for the foreseeable future.

Additional Reading

Barnes, Johnathan. The Toils of Scepticism. Cambridge, London: Cambridge University Press, 1990. This is a technical but clear and engaging exposition of Pyrrhonian Skepticism by one of the foremost Oxford philosophers. Includes bibliographical references.

Hookway, Christopher. Scepticism. London: Routledge, 1990. Chapters 1 and 2 give a general account of Pyrrhonian Skepticism through the view of Sextus Empiricus. The rest of this book contains a detailed account of the influence of skepticism in various areas of modern philosophy.

Popkin, Richard H. The History of Scepticism: From Erasmus to Spinoza. Los Angeles: University of California Press, 1979. This is an excellent, readable, and informed historical treatment of Sextus and Pyrrhonian influences on the foundation of modern Western philosophy. In chapter 2, Popkin presents a clear and accessible account of the revival of skepticism in Europe in the sixteenth century.

Schmitt, C. B. “The Rediscovery of Ancient Skepticism in Modern Times.” In The Skeptical Tradition, edited by Myles Burnyeat. Berkeley: University of California Press, 1983. This article gives a thorough account of the accidental rediscovery of Sextus’s two books and their effect on the modern philosophy of the West. Chapters 2-9 of this book are basically devoted to discussions of ancient and Pyrrhonian Skepticism, and chapters 10 to 17 are excellent expositions of modern skepticism as a byproduct of its ancient Hellenistic prototype.

Sharples, Robert W. Stoics, Epicureans, and Sceptics: An Introduction to Hellenistic Philosophy. London: Routledge, 1996. Accessible reading on history and the principles of Sextus’s Pyrrhonism. The chapters on stoicism and Epicureanism are quite helpful in understanding Sextus’s arguments, for they are directed partially against these Hellenistic philosophies.

Zeller, Eduard. The Stoics, Epicureans, and Sceptics. Translated from the German by Oswald J. Reichel. New York: Russell and Russell, 1962. Chapters 22 and 23 describe in a clear and detailed manner the Pyrrhonian and the Academic versions of ancient Skepticism.