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Pyrrhonism is a school of philosophical skepticism founded by Pyrrho in the fourth century BCE. It is best known through the surviving works of Sextus Empiricus, writing in the late second century or early third century CE.
Pyrrho of Elis (c. 360 – c. 270 BCE) and his teacher Anaxarchus, both Democritean philosophers, traveled to India with Alexander the Great's army where Pyrrho was said to have studied with the magi and the gymnosophists, and where he was influenced by Buddhist teachings, most particularly the three marks of existence. After returning to Greece, Pyrrho started a new line of philosophy now known as "Pyrrhonism." His teachings were recorded by his student Timon of Phlius, most of whose works have been lost.
Pyrrhonism as a school was either revitalized or re-founded by Aenesidemus in the first century BCE. This phase of Pyrrhonism, starting with Aenesidemus and going through the last known Pyrrhonist of antiquity, Saturninus, is sometimes referred to as "neo-Pyrrhonism." Others use the term "neo-Pyrrhonism" to refer to modern Pyrrhonists such as Robert Fogelin.
Although Cicero, Seneca the Younger, and Julian the Apostate each mention that Pyrrhonism had died out at the time of their writings, other writers mention the existence of Pyrrhonists. Aenesidemus was a contemporary of Cicero. Diogenes Laertius mentions Pyrrhonists who were roughly contemporary with Seneca. Pseudo-Clement (c. 300-320 CE) mentions Pyrrhonists in his Homilies. Agathias reports a Pyrrhonist named Uranius in the middle of the 6th century CE.
The recovery and publishing of the works of Sextus Empiricus in the sixteenth century ignited a revival of interest in Pyrrhonism.
Pyrrhonism is the earliest Western form of philosophical skepticism. As with other Hellenistic philosophies such as Stoicism, Peripateticism and Epicureanism, eudaimonia is the Pyrrhonist goal of life. According to the Pyrrhonists, it is one's opinions about non-evident matters (i.e., dogma) that prevent one from attaining eudaimonia. As with Epicureanism, Pyrrhonism places the attainment of ataraxia (a state of equanimity) as the way to achieve eudaimonia. To bring the mind to ataraxia Pyrrhonism uses epoché (suspension of judgment) regarding all non-evident propositions. Pyrrhonists dispute that the dogmatists – which includes all of Pyrrhonism's rival philosophies – have found truth regarding non-evident matters. For any non-evident matter, a Pyrrhonist makes arguments for and against such that the matter cannot be concluded, thus suspending belief and thereby inducing ataraxia.
Although Pyrrhonism's objective is eudaimonia, it is best known for its epistemological arguments, particularly the problem of the criterion, and for being the first Western school of philosophy to identify the problem of induction and the Münchhausen trilemma.
Pyrrhonist practice is for the purpose of achieving epoché, i.e., suspension of judgment. The core practice is through setting argument against argument. To aid in this, the Pyrrhonist philosophers Aenesidemus and Agrippa developed sets of stock arguments known as "modes" or "tropes."
The ten modes of Aenesidemus
Aenesidemus is considered the creator of the ten tropes of Aenesidemus (also known as the ten modes of Aenesidemus)—although whether he invented the tropes or just systematized them from prior Pyrrhonist works is unknown. Sextus Empiricus attributed them simply to the earlier Pyrrhonists. Diogenes Laeritius attributed them to Aenesidemus. The title of a lost work of Plutarch's (On Pyrrho's Ten Modes) appears to attribute the modes to Pyrrho. The tropes represent reasons for epoché (suspension of judgment). These are as follows:
- "The same impressions are not produced by the same objects owing to the differences in animals."
- The same impressions are not produced by the same objects owing to the differences among human beings.
- The same impressions are not produced by the same objects owing to the differences among the senses.
- Owing to the "circumstances, conditions or dispositions," the same objects appear different. The same temperature, as established by instrument, feels very different after an extended period of cold winter weather (it feels warm) than after mild weather in the autumn (it feels cold). Time appears slow when young and fast as aging proceeds. Honey tastes sweet to most but bitter to someone with jaundice. A person with influenza will feel cold and shiver even though she is hot with a fever.
- Based on positions, distances, and locations; for owing to each of these the same objects appear different; for example, the same porch when viewed from one of its corners appears curtailed, but viewed from the middle symmetrical on all sides; and the same ship seems at a distance to be small and stationary, but from close at hand large and in motion ; and the same tower from a distance appears round but from a near point quadrangular.
- “We deduce that since no object strikes us entirely by itself, but along with something else, it may perhaps be possible to say what the mixture compounded out of the external object and the thing perceived with it is like, but we would not be able to say what the external object is like by itself."
- "Based, as we said, on the quantity and constitution of the underlying objects, meaning generally by "constitution" the manner of composition." So, for example, goat horn appears black when intact and appears white when ground up. Snow appears white when frozen and translucent as a liquid.
- "Since all things appear relative, we will suspend judgement about what things exist absolutely and really existent. Do things which exist "differentially" as opposed to those things that have a distinct existence of their own, differ from relative things or not? If they do not differ, then they too are relative; but if they differ, then, since everything which differs is relative to something..., things which exist absolutely are relative."
- "Based on constancy or rarity of occurrence." The sun is more amazing than a comet, but because we see and feel the warmth of the sun daily and the comet rarely, the latter commands our attention.
- "There is a Tenth Mode, which is mainly concerned with Ethics, being based on rules of conduct, habits, laws, legendary beliefs, and dogmatic conceptions."
Superordinate to these ten modes stand three other modes:
- that based on the subject who judges (modes 1, 2, 3 & 4).
- that based on the object judged (modes 7 & 10).
- that based on both subject who judges and object judged (modes 5, 6, 8 & 9)
Superordinate to these three modes is the mode of relation.
The five modes of Agrippa
These "tropes" or "modes" are given by Sextus Empiricus in his Outlines of Pyrrhonism. According to Sextus, they are attributed only "to the more recent skeptics" and it is by Diogenes Laërtius that we attribute them to Agrippa. The five tropes of Agrippa are:
- Dissent – The uncertainty demonstrated by the differences of opinions among philosophers and people in general.
- Progress ad infinitum – All proof rests on matters themselves in need of proof, and so on to infinity, i.e., the regress argument.
- Relation – All things are changed as their relations become changed, or, as we look upon them from different points of view.
- Assumption – The truth asserted is based on an unsupported assumption.
- Circularity – The truth asserted involves a circularity of proofs.
According to the mode deriving from dispute, we find that undecidable dissension about the matter proposed has come about both in ordinary life and among philosophers. Because of this we are not able to choose or to rule out anything, and we end up with suspension of judgement. In the mode deriving from infinite regress, we say that what is brought forward as a source of conviction for the matter proposed itself needs another such source, which itself needs another, and so ad infinitum, so that we have no point from which to begin to establish anything, and suspension of judgement follows. In the mode deriving from relativity, as we said above, the existing object appears to be such-and-such relative to the subject judging and to the things observed together with it, but we suspend judgement on what it is like in its nature. We have the mode from hypothesis when the Dogmatists, being thrown back ad infinitum, begin from something which they do not establish but claim to assume simply and without proof in virtue of a concession. The reciprocal mode occurs when what ought to be confirmatory of the object under investigation needs to be made convincing by the object under investigation; then, being unable to take either in order to establish the other, we suspend judgement about both.
With reference to these five tropes, that the first and third are a short summary of the earlier Ten Modes of Aenesidemus. The three additional ones show a progress in the Pyrrhonist system, building upon the objections derived from the fallibility of sense and opinion to more abstract and metaphysical grounds.
According to Victor Brochard “the five tropes can be regarded as the most radical and most precise formulation of skepticism that has ever been given. In a sense, they are still irresistible today.”
Criteria of action
Pyrrhonist decision making is made according to what the Pyrrhonists describe as the criteria of action holding to the appearances, without beliefs in accord with the ordinary regimen of life based on:
- the guidance of nature, by which we are naturally capable of sensation and thought
- the compulsion of the pathé by which hunger drives us to food and thirst makes us drink
- the handing down of customs and laws by which we accept that piety in the conduct of life is good and impiety bad
- instruction in crafts and the arts
- Not more, nothing more (a saying attributed to Democritus)
- Perhaps, it is possible, maybe
- I withhold assent
- I determine nothing (Montaigne created a variant of this as his own personal motto, "Que sçay-je?" – "what do I know?")
- Everything is indeterminate
- Everything is non-apprehensible
- I do not apprehend
- To every argument an equal argument is opposed
Connections with other philosophies
Pyrrhonism is often contrasted with Academic Skepticism, a similar but distinct form of Hellenistic philosophical skepticism. Dogmatists claim to have knowledge, Academic Skeptics claim that knowledge is impossible, while Pyrrhonists assent to neither proposition, suspending judgment on both. The second century Roman historian Aulus Gellius describes the distinction as follows:
"...the Academics apprehend (in some sense) the very fact that nothing can be apprehended, and they determine (in some sense) that nothing can be determined, whereas the Pyrrhonists assert that not even that seems to be true, since nothing seems to be true."
Following the death of Timon, the Platonic Academy became the primary advocate of skepticism until the mid-first century BCE. While early Academic Skepticism was influenced in part by Pyrrho, it grew more and more dogmatic until Aenesidemus broke with the Academics to revive Pyrrhonism in the first century BCE, denouncing the Academy as "Stoics fighting against Stoics." Some later Pyrrhonists, such as Sextus Empiricus, go so far as to claim that Pyrrhonists are the only real skeptics, dividing all philosophy into the dogmatists, the Academics, and the skeptics.
The summary of Pyrrho's teaching preserved in the "Aristocles passage" shows signs of Buddhist philosophical influence. This text is:
Whoever wants eudaimonia (to live well) must consider these three questions: First, how are pragmata (ethical matters, affairs, topics) by nature? Secondly, what attitude should we adopt towards them? Thirdly, what will be the outcome for those who have this attitude?" Pyrrho's answer is that "As for pragmata they are all adiaphora (undifferentiated by a logical differentia), astathmēta (unstable, unbalanced, not measurable), and anepikrita (unjudged, unfixed, undecidable). Therefore, neither our sense-perceptions nor our doxai (views, theories, beliefs) tell us the truth or lie; so we certainly should not rely on them. Rather, we should be adoxastous (without views), aklineis (uninclined toward this side or that), and akradantous (unwavering in our refusal to choose), saying about every single one that it no more is than it is not or it both is and is not or it neither is nor is not. The outcome for those who actually adopt this attitude, says Timon, will be first aphasia (speechlessness, non-assertion) and then ataraxia (freedom from disturbance), and Aenesidemus says pleasure.
According to Christopher I. Beckwith's analysis of the Aristocles Passage, adiaphora (anatta), astathmēta (dukkha), and anepikrita (anicca) are strikingly similar to the Buddhist three marks of existence, indicating that Pyrrho's teaching is based on Buddhism. Beckwith contends that the 18 months Pyrrho spent in India were long enough to learn a foreign language, and that the key innovative tenets of Pyrrho's skepticism were only found in Indian philosophy at the time and not in Greece. Other scholars, such as Stephen Batchelor and Charles Goodman question Beckwith's conclusions about the degree of Buddhist influence on Pyrrho.
Other similarities between Pyrrhonism and Buddhism include a version of the tetralemma among the Pyrrhonist maxims and a parallel with the Buddhist Two Truths Doctrine. In Pyrrhonism the Buddhist concept of "ultimate" (paramārtha) truth corresponds with truth as defined via the criterion of truth, which in Pyrrhonism is seen as undemonstrated, and therefore nothing can be called "true" with respect of it being an account of reality. The Buddhist concept of "conventional" or "provisional" (saṁvṛti) truth corresponds in Pyrrhonism to truth defined via the Pyrrhonist criterion of action, which is used for making decisions about what to do.
Nagarjuna's Madhyamaka philosophy is particularly similar to Pyrrhonism. According to Thomas McEvilley this is because Nagarjuna was likely influenced by Greek Pyrrhonist texts imported into India.
Except for the works of Sextus Empiricus and Diogenes Laërtius, the texts about ancient Pyrrhonism have been lost, except for a summary of Pyrrhonian Discourses by Aenesidemus, preserved by Photius, and a summary of Pyrrho's teaching preserved by Eusebius, quoting Aristocles, quoting Pyrrho's student Timon, in what is known as the "Aristocles passage."
Pyrrhonism so influenced Arcesilaus, the sixth scholarch of the Platonic Academy that Arcesilaus reformed the teaching of the Academy to be nearly identical to Pyrrhonism thus initiating the Academic Skepticism of the Middle Academy.
The Pyrrhonist school influenced and had substantial overlap with the Empiric school of medicine. Many of the well-known Pyrrhonist teachers were also Empirics, including: Sextus Empiricus, Herodotus of Tarsus, Heraclides, Theodas, and Menodotus. However, Sextus Empiricus said that Pyrrhonism had more in common with the Methodic school in that it “follow[s] the appearances and take[s] from these whatever seems expedient.”
Because of the high degree of similarity between the Buddhist philosopher Nagarjuna's Madhyamaka philosophy and Pyrrhonism, particularly as detailed in the surviving works of Sextus Empiricus, Thomas McEvilley suspects that Nagarjuna was influenced by Greek Pyrrhonist texts imported into India.
Pyrrhonism began to regain prominence starting in the late fifteenth century and the sixteenth century. The publication of the works of Sextus Empiricus, particularly a widely influential translation by Henri Estienne published in 1562, played a major role in Renaissance and Reformation thought. Philosophers of the time used his works to source their arguments on how to deal with the religious issues of their day. Major philosophers such as Michel de Montaigne, Marin Mersenne, and Pierre Gassendi later drew on the model of Pyrrhonism outlined in Sextus Empiricus’ works for their own arguments. This resurgence of Pyrrhonism has sometimes been called the beginning of modern philosophy.
It has also been suggested that Pyrrhonism provided the skeptical underpinnings that René Descartes drew from in developing his influential method of Cartesian doubt and the associated turn of early modern philosophy towards epistemology. The Pyrrhonian formulation of skepticism would also go on to have a considerable influence on David Hume.
Pyrrhonism also affected the development of historiography. Historical Pyrrhonism emerged during the early modern period and played a significant role in shaping modern historiography. Historical Pyrrhonism questioned the possibility of any absolute knowledge from the past and transformed later historians' selection of and standard for reliable sources.
A revival of the use of "Pyrrhonism" as a synonym for "skepticism" occurred during the seventeenth century.
Fallibilism is a modern, fundamental perspective of the scientific method, as put forth by Karl Popper and Charles Sanders Peirce, that all knowledge is, at best, an approximation, and that any scientist always must stipulate this in her or his research and findings. It is, in effect, a modernized extension of Pyrrhonism. Indeed, historic Pyrrhonists sometimes are described by modern authors as fallibilists and modern fallibilists sometimes are described as Pyrrhonists.
326-270 BCE Pyrrho
270-235 Timon of Phlius
???-??? Euphranor of Seleucia
???-??? Eubulus of Alexandria
???-??? Ptolemy of Cyrene
c. 100 Heraclides of Tarentum
c. 50 Aenesidemus
???-??? Antiochus of Laodicea on the Lycus
c 100 CE Menodotus of Nicomedia
c. 120 Herodotus of Tarsus
c. 160 Sextus Empiricus
c. 200 Saturninus
List of Pyrrhonist philosophers
- Agrippa the Skeptic
- Hecataeus of Abdera
- Heraclides of Tarentum
- Herodotus of Tarsus
- Menodotus of Nicomedia
- Sextus Empiricus
- Theodas of Laodicea
- Academic Skepticism
- Apophatic theology
- Cognitive closure (philosophy)
- De Docta Ignorantia
- Nassim Nicholas Taleb
- The Hedgehog and the Fox
- List of unsolved problems in philosophy
- Popkin, Richard Henry (2003). The history of scepticism : from Savonarola to Bayle. Popkin, Richard Henry, 1923- (Rev. and expanded ed.). Oxford: Oxford University Press. ISBN 0198026714. OCLC 65192690.
- "Diogenes Laërtius, Lives of Eminent Philosophers Book IX - Chapter 11. PYRRHO (c. 360-270 b.c.)". www.perseus.tufts.edu.
- Beckwith, Christopher I. (2015). Greek Buddha: Pyrrho's Encounter with Early Buddhism in Central Asia (PDF). Princeton University Press. p. 28. ISBN 9781400866328.
- Stéphane Marchand, "Sextus Empiricus’ Style Of Writing", in New Essays on Ancient Pyrrhonism, p 113
- Michael Williams, "Fogelin's Neo-Pyrrhonism", International Journal of Philosophical Studies Volume 7, Issue 2, 1999, p141
- Smith, Plínio Junqueira; Bueno, Otávio (7 May 2016). Zalta, Edward N. (ed.). Skepticism in Latin America. Metaphysics Research Lab, Stanford University – via Stanford Encyclopedia of Philosophy.
- Seneca the Younger, Nat Quaest VII xxxii 2
- Epistles lxxxix 301C
- Pseudo-Clement, Homilies, 13.7
- Agathias II 29-32, cited in Jonathan Barnes, Mantissa 2015 p. 652
- Thorsrud, Harald (2009). Ancient scepticism. Stocksfield [U.K.]: Acumen. p. 17. ISBN 978-1-84465-409-3. OCLC 715184861.
The History of ancient scepticism officially begins with the enigmatic character, Pyrrho of Elis
- Pulleyn, William (1830). The Etymological Compendium, Or, Portfolio of Origins and Inventions. T. Tegg. pp. 353.
- Mauro Bonazzi, "Plutarch on the Differences Between the Pyrrhonists and Academics", Oxford Studies in Ancient Philosophy, 2012 
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 27
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 47
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 55
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p.61
- Sextus Empiricus, Outlines of Pyrrhonism, Book I Section 118 Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p.69-71
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p.73
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p.77
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 79
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 81
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 83
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 85
- Sextus Empiricus, Outlines of Pyrrhonism, Trans. R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, pp. 25–27
- Diogenes Laërtius, ix.
- Sextus Empiricus, Pyrrhōneioi hypotypōseis i., from Annas, J., Outlines of Scepticism Cambridge University Press. (2000).
- Brochard, V., The Greek Skeptics.
- Sextus Empiricus, Outlines of Pyrrhonism Book I Chapter 11 Section 23
- Sextus Empiricus Outlines of Pyrrhonism Book I Chapter 18
- Sextus Empiricus Outlines of Pyrrhonism Book II Chapter 30
- Klein, Peter (2015). "Skepticism". Stanford Encyclopedia of Philosophy. Archived from the original on 25 July 2018. Retrieved 19 March 2021.
The Pyrrhonians withheld assent to every non-evident proposition. That is, they withheld assent to all propositions about which genuine dispute was possible, and they took that class of propositions to include both the (meta) proposition that we can have knowledge of EI-type propositions and the (meta) proposition that we cannot have knowledge. Indeed, they sometimes classified the Epistemists and the Academic Skeptics together as dogmatists because the Epistemists assented to the proposition that we can have knowledge, while the Academic Skeptics assented to the denial of that claim.
- Sextus, Empiricus (1990). Outlines of pyrrhonism. Robert Gregg Bury. Buffalo, N.Y.: Prometheus Books. ISBN 0-87975-597-0. OCLC 23367477.
Those who believe they have discovered it are the "dogmatists," specially so called - Aristotle, for example, and Epicurus and the Stoics and certain others; Cleitomachus and Carneades and other Academics treat it as inapprehensible:the skeptics keep on searching. Hence it seems reasonable to hold the main types of philosophy are three- the dogmatic, the Academic, and the skeptic.
- Thorsrud, Harald (2009). Ancient scepticism. Stocksfield [U.K.]: Acumen. ISBN 978-1-84465-409-3. OCLC 715184861.
Both Academic and Pyrrhonian Scepticism develop in complicated ways in response to each other and in response to their common dogmatic opponents.
- Popkin, Richard (1995). The Cambridge dictionary of philosophy. Robert Audi. Cambridge. p. 741. ISBN 0-521-40224-7. OCLC 32272442.
Skepticism: Those Academic thinkers who developed sets of arguments to show either that no knowledge is possible (Academic Skepticism) or that there is not sufficient or adequate evidence to tell if any knowledge is possible. If the latter is the case then these thinkers advocated suspending judgment on all questions concerning knowledge (Pyrrhonian Skepticism).
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- Thorsrud, Harald (2009). Ancient scepticism. Stocksfield [U.K.]: Acumen. ISBN 978-1-84465-409-3. OCLC 715184861.
- Thorsrud, Harald (2009). Ancient scepticism. Stocksfield [U.K.]: Acumen. pp. 120–121. ISBN 978-1-84465-409-3. OCLC 715184861.
Pyrrhonism, in whatever form it might have taken after Timon's death in 230 BCE, was utterly neglected until Aenesidemus brought it back to public attention
- Thorsrud, Harald (2009). Ancient scepticism. Stocksfield [U.K.]: Acumen. p. 45. ISBN 978-1-84465-409-3. OCLC 715184861.
So while Pyrrho's influence is significant, it does not shape the contours of Arcesilaus' scepticism nearly as much as the influence of Plato and Socrates.
- Thorsrud, Harald (2009). Ancient scepticism. Stocksfield [U.K.]: Acumen. pp. 102–103. ISBN 978-1-84465-409-3. OCLC 715184861.
Aenesidemus criticized his fellow Academics for being dogmatic...Aenesidemus committed his scepticism to writing probably some time in the early-to-mid first century BCE...leading Aenesidemus to dismiss them as "Stoics fighting against Stoics."
- Beckwith, Christopher I. (2015). Greek Buddha: Pyrrho's Encounter with Early Buddhism in Central Asia (PDF). Princeton University Press. pp. 22–23. ISBN 9781400866328.
- Beckwith, Christopher I. (2015). Greek Buddha: Pyrrho's Encounter with Early Buddhism in Central Asia. Princeton University Press. p. 221. ISBN 9781400866328.
- Stephen Batchelor "Greek Buddha: Pyrrho's encounter with early Buddhism in central Asia", Contemporary Buddhism, 2016, pp 195-215
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- Sextus Empricus, Outlines of Pyrrhonism Book 1, Section 19
- McEvilley, Thomas (2002). The Shape of Ancient Thought. Allworth Communications. ISBN 1-58115-203-5., p. 474
- Adrian Kuzminski, Pyrrhonism: How the Ancient Greeks Reinvented Buddhism 2008
- Thomas McEvilley, The Shape of Ancient Thought 2002 pp499-505
- Sarah Bakewell, How to Live: Or A Life of Montaigne in One Question and Twenty Attempts at an Answer 2011 p 127 ISBN 1590514831
- Sextus Empiricus, Outlines of Pyrrhonism Book I Chapter 33
- Sextus Empiricus, Outlines of Pyrrhonism I.237, trans. Etheridge (Scepticism, Man, and God, Wesleyan University Press, 1964, p. 98).
- Popkin, Richard Henry (2003). The History of Scepticism : from Savonarola to Bayle (Revised ed.). Oxford: Oxford University Press. ISBN 9780198026716. OCLC 65192690.
- Matytsin, Anton M. (6 November 2016). The specter of skepticism in the age of Enlightenment. Baltimore. ISBN 9781421420530. OCLC 960048885.
- Dialogues Concerning Natural Religion, page 7, section 23.
- Powell, Thomas C. "Fallibilism and Organizational Research: The Third Epistemology", Journal of Management Research 4, 2001, pp. 201–219.
- "Ancient Greek Skepticism" at the Internet Encyclopedia of Philosophy.
- Diogenes Laërtius, "Lives of the Eminent Philosophers", Book 9, Chapter 12, Section 116
- Pyrrhonism discussion group on Facebook
- Website for the Modern Pyrrhonism Movement
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