Not all skeptics are atheists, but skepticism is a life stance so common to secular thinkers that a glance at skeptic philosophy will be of interest to people in the secular community.  Skepticism in the Western world began with the ancient Greeks.  There were two forms at that time: assertive and non-assertive.  Plato’s Academy (387 B.C.E. – 83 B.C.E.) originated assertive skepticism. Socrates (5th Century B.C.E.) claimed that the only thing he knew was that he knew nothing.  Arcesilaus also asserted that nothing was known.  After him came Carneades who maintained the stance that no knowledge was possible.  These Academy philosophers took an assertive, argumentative approach to skepticism.

Non-assertive skepticism began in the 4th century B.C.E. and is called pyrrhonism.  Pyrrho of Elis is considered the founder of skepticism by many scholars.  His works have been lost and all we know of his philosophy is from the texts of Sextus Empiricus (2nd century C.E.) Ancient pyrrhonism was not an epistemology because it had no theory of knowledge and worked to undermine more dogmatic epistemologies.[1] This total suspension of judgment was called “epoche.” It was a step on the way to mental tranquility, “ataxaria.”  Non-assertive skepticism entertains no judgments and accepts the world as it is, a type of life philosophy, a means to attain the “good life.”

Sextus Empiricus was a Roman physician in the 2nd century C.E.  His books, in several volumes, are classic works of doubt.  Skeptics such as Sextus Empiricus would set up a proposition into two different positions, and then argue a dependent notion for each side, until they found a contradiction. At that point they would dismiss the original idea.  Empiricus is well known for beginning arguments with propositions that would not deny the gods.  He would then render the entire gods concept so absurd by his reasoning that he effectively cancelled it out.  His interesting arguments on god can be found in Book Three of the outline of pyrrhonism, “On God,” and in “Against the Dogmatists” in a section titled “Concerning the Gods.”[2]

Ascendant Christianity took philosophy over and skeptic philosophy went into decline until Descartes, (1596-1650 A.C.E.) the originator of modern philosophy.  In his Meditations (1641), he ponders if there is any certainty with regard to any knowledge.  He decided there was none.  Descartes used radical skeptical doubt to destroy belief in any theory.  He used the device of the invisible demon, who might be tricking him into perceiving himself performing mathematical calculations in the world; and yet none of those things might be true, neither the calculations nor the world.  He decided only his thought existed.  From this concept came the famous statement: “I think, therefore I am.” Descartes’ “Cogito, ergo sum” was not the final answer.  Critics pointed out that the demon could deceive us about our thoughts.


The British empiricists of the 17th and 18th Centuries depreciated reason and stressed empiricism.  Empiricism prevails today but the two philosophical methods remain in conflict.  Locke, Berkeley and Hume addressed the issue that our ideas are all we can positively know.  Each of them queried the question of how can we know the external world corresponds to our ideas? Locke’s theories led to a form of skepticism, though he was not a skeptic.  Berkeley set out to defeat atheism and ended up eliminating the external world entirely from his theory.[3]

David Hume (1711-1776) is considered one of the greatest British philosophers.  He was what he called a “mitigated skeptic,” but his views on knowledge are extreme and brilliant at the same time. Hume believed that our knowledge of the existence of anything outside ourselves could ultimately derive from experience alone. We can never know with certainty whether a material world exists or not.[4]

Causality was also a matter of doubt for Hume.  You see a ball fall and you assume gravity caused it to fall. But Hume denies that is the case.  The two are causally connected in our mind.  A happened, then B happened.  We have no real proof even if the sequence happens over and over.

Hume also began questioning the idea of a self (which the Postmodern philosophers would take up in the 20th Century.)  He found when he introspected, that he could only contemplate his thoughts and emotions, not a continuous self.  He decided that there is no observational evidence of a self, or of a god. He stated that “a miracle is a violation of the laws of nature and since firm and unalterable experience has established these laws, the proof against a miracle, from the very nature of fact is as entire as any argument from experience can possibly be imagined.”

Hume’s much quoted phrase, that “Reason is the slave of the passions,” is another of his important concepts.  He thought that people can only live by custom.  We do not know the sun will rise again the next morning, but habit allows us to expect it.  That is why he called himself a mitigated skeptic.  Even though Hume believed there were virtually no moral “truths” that could be proved to be certain, he thought that men’s empathetic feelings of sympathy for other humans and respect for the social customs of their lands would serve to keep people orderly and content.

Immanuel Kant (1724-1804) posited that we can’t know the thing-in-itself and we cannot apprehend the real world correctly through our limited sense apparatus.  Charles Sanders Pierce, the American pragmatist, was an empiricist as was John Dewey. (See Naturalism – Pragmatism.) Karl Popper’s falsifability is the concept that scientific theories must always be provisional and that scientists should think of ways that their theories could be falsified. Popper was a very influential 20th Century philosopher who would not call himself a skeptic, but some thinkers find his general approach similar to Pyrrho.  Bertrand Russell, the 20th Century British philosopher, was a renowned thinker and social critic.  Russell’s skepticism is a version of mitigated skepticism, namely, that some information is more reliable than other information, but that none of it (except for primitive data) can be absolutely certain.[5]

Jacques Derrida, the 20th Century French philosopher, was an anti-Cartesian, who followed the German philosophers, such as Martin Heidegger.  He was greatly influenced by Saussure, a 20th Century Swiss linguist, who was a holist about semantics.  Saussure maintained meaning did not lie in single words or sentences but language as a whole, as did W.V. Quine.  Popkin states that Derrida was a radical skeptic.  Derrida found that any text can be interpreted in more than one way.  He maintained there is no such thing as an objective or true interpretation of any text.  Popkin maintains that Derrida believed man was the measure of all things.[6] That stance would make his thinking similar to Pyrrho.

Modern Skepticism

Skepticism in recent years has taken two distinct paths.  Skepticism in academe is involved with abstract thinking about knowledge and its related enquiries of knowledge origins and similar concerns. This pursuit is often viewed as arcane and irrelevant by non-professionals.

The second direction of skepticism is a populist one, which has had some popularity and interest.  Contemporary skepticism applies critical thinking to fads, follies, and frauds that take people in. These frauds and present-day myths might be scientific, medical, psychological, social and so on.  The contemporary skeptical movement has now spread all over the world.  There are several important organizations in the United States for the promotion of skepticism.  They are the Committee for Skeptical Inquiry (CSI), The Skeptics Society and the James Randi Educational Foundation.  Michael Shermer is the co-founder of the Skeptics Society and a well-known author and lecturer.  The Skeptics Society publishes Skeptic Magazine.  Shermer is a force for applying scientific methods and naturalistic explanations for what are described as supernatural events. 

The Committee for the Scientific Investigation of Claims of the Paranormal (CISCOP) and its Skeptical Inquirer Journal have attempted to apply scientific methods to uncover the truth claims of paranormal events.  The Committee for the Scientific Examination of Religion, founded by the Council for Secular Humanism and its Journal, Free Inquiry, now operates under the auspices of The Center for Inquiry.  This organization investigates such areas as religious claims and biblical inaccuracies and applies scientific and other enquiries into claims of prayer, faith healing and so on.[7]

Carl Sagan, the 20th Century astronomer and author, spent many years promoting science and skepticism.  The term “scientific skepticism” may have originated with him.[8]

Our brief glance at the history of skepticism and its present-day strength and growth is very encouraging.  The media pick up the absurd claims of faith healers, of miracles, and fads that bilk people of their money and time. They encourage sloppy thinking and irrational belief systems in the credulous. The work of contemporary skeptics is very valuable.  They have taken doubt out of the academy and put it in the world of everyday, where the voices of hucksters, charlatans and cranks threaten to drown out the light of reason.

Video of Lecture: Skepticism

Lecture: Skepticism

Video of Discussion: Skepticism

Discussion: Skepticism


1 Martinich, A.P. “Epistemology,” in Encyclopedia Britannica, Vol. 18 (1990.) 476.

2 Hecht, Jennifer Michael. Doubt: A History.  New York: Harper Collins, 2004. 162-164.

3 Popkin, Richard H. and Avrum Stroll.  Skeptical Philosophy for Everyone.  Amherst, New York: Prometheus Books, 2002.

4 Magee, Bryan.  The Story of Philosophy. New York: DK Publishing, 2001. 114.

5 Popkin, 112.

6 Popkin, 140.

7 Kurtz,Paul. “Skepticism.” In Tom Flynn, ed. The New Encyclopedia of Disbelief. Amherst, New York: Prometheus Books, 2007. 717.

8 “The History of Skepticism.” The Skeptic’s Dictionary. (Web)

Recomended Books

Part I lists books that deal with Classical Skepticism.  Part 2 lists books that deal with Contemporary Skepticism.

Part 1 Classical Skepticism

Empiricus, Sextus.  Sextus Empiricus: Outlines of Skepticism. Second ed. Ed & Tras. Julia Annas and Jonathan Barnes. Cambridge, UK; Cambridge University Press, 2000.

Empiricus’ volume, divided into three parts, is virtually the only surviving record of the teachings of the 4th Century B.C.E. Pyrrho of Elis.  This particular translation is considered the best, but there are also fine ones by Bury; the Oxford Edition of Sextus, as well as the 4 Volume Loeb Library are both excellent. Sextus Empiricus’ work was discovered in the 16th Century Italian Renaissance.  This text argues the skeptics’ case against the Dogmatists.

Many readers and critics mention the doubt of the Postmoderns, comparing their thinking to the tenets in this text, but Sextus Empiricus was more radical then they.  By the time he has finished, Empiricus has maintained that one can never know anything for certain, that there are only probabilities.  He states that the Dogmatists are sick and need the “cure” of skepticism.  His writing style is clear and concise, and relatively easy to understand.  His ideas are very bracing in a contemporary time when credulity concerning politics, culture, science, medicine and its alternatives seem to reign supreme.  Whether the book achieves the goal Sartre also (See Existentialism) attempted: “to work out a coherent atheism,” is still in play.  Certainly Empiricus teaches the reader to be more critical of truth claims.

This is a highly recommended work for readers with some acquaintance with philosophy.  Beginning readers will likely find it dry and repetitious.

Hume, David. (1748) Hume: An Enquiry concerning Human Understanding. Stephen Buckle, ed. Cambridge: Cambridge University Press, 2007.

This volume was written in defense of an earlier work of Hume’s on the same topic.  While often described as a moderate or mitigated skeptic, Hume is also associated with radical skepticism.  Certainly his claim that there is no causation that we can be sure of is an arresting idea.  If we see something fall, we cannot simply assume gravity has been responsible.  All we see is “constant conjunction” and what appears to be caused. We cannot know (Hume is much taken with epistemology) that we know natural law.  His concept is very bold and this particular proposition remains difficult to deal with up to the present day.  Bertrand Russell said that Hume makes a claim that cannot be refuted and that no one can accept.  Hume questions causation and most received opinion.  As with Sextus Empiricus, Hume helps us to think and perhaps frees us from unquestioning faith in religion, science, and more.

Hume is an elegant writer and not too difficult to understand.  The atheist reader may not always agree, but will appreciate his arguments.  Highly recommended.

Montaigne, de Michael.  (1580) The Complete Essays. Ed.&Tras.M.A.Screech. New York: Penguin Classics, 1993.

Montaigne is fortunate to have two translators who have done justice to his work.  The Screech edition is listed here, but the Donald Frame translation is equally fine.

Montaigne retired from an active life in politics to his estate at 33 years old and spent his time writing these essays.  He is a skeptic through and through.  There are different opinions as to whether he was a believer in god, an agnostic or atheist.  Suffice to say, the Inquisition looked at his writings closely and held them for a time. He seems to have gotten around the threat by scrutinizing everything on earth skeptically and leaving metaphysical questions concerning god unwritten. 

Montaigne is erudite, witty, deep and charming.  The book, over 1000 pages, is to be dipped into here and there, at will.  This is not a scholarly volume in the sense that it details the propositions of skepticism.  It is a wise look at the limits of reason, man’s opinion that he “knows” something, and that only a fool is bound to his body by fear of death.  He believed that custom and law defined religion and not reason.  A caveat: readers who come across references that Montaigne believed in god should take the statement with a grain of salt. 

Popkin, Richard. (1960.) The History of Skepticism: From Savonarola to Bayle. Expanded Ed.  U.S.A.: Oxford University Press, 2003. 

Popkin’s book is very elucidating for the reader interested in skepticism.  This is the second edition after the first publication some fifty years ago.  During that time research on the history and role of skepticism grew all over the world.  Popkin’s work was translated into Spanish, Italian and Portugese.  His book has been published in the United States, England, Canada, Spain, Argentina, Italy, Brazil and France.  Popkin’s new edition of The History of Skepticism covers all the primary philosophies of the 17th Century and a large number of secondary philosophers.  His book certainly corroborates the thesis that most early modern philosophers were preoccupied at some point with establishing or refuting skepticism.

History is well researched and well written.  It is considered the definitive word on the history of skepticism.  Popkin’s Skeptical Philosophy for Everyone (2002) brings the history of skepticism into the modern world and is also an excellent text.

Part 2   Contemporary Skepticism

Gardner, Martin.  Fads and Fallacies in the Name of Science. 2nd Ed. New York: Dover, 1957.

The late Gardner’s volume is now somewhat dated but is worth reading.  It was one of the sparks to the beginning modern skeptical movement.  Some of the chapters are: “Dowsing Rods and Doodlebugs,” “Geology versus Genesis,” “Flying Saucers and Down with Einstein,” (about people who think they are smarter than Einstein.)

Fads is credited by some readers with helping them to attain critical thinking skills.  Certainly in a culture filled with hostility to reason, with one of the prevailing mottoes of “just believe,” books like Gardner’s are a tonic. His style is dry, non-malicious and witty.  Some readers dislike the fact that Gardner never discusses the why of the cranks he writes about.  Surely that would fill several more volumes.

Park, Robert. Voodoo Science: The Road From Foolishness to Fraud. New York: Oxford University Press, 2001.

Dr. Park is a professor of physics.  He has written for the New York Times and the Washington Post.  In this volume, Park is attempting to educate readers that the universe we live in is governed by certain laws and that those laws cannot be broken, gone around, or dodged by magic, miracles, or delusions.  Park is quite good at explaining the laws of physics and chemistry to non-professional readers.

Park takes a few easy shots at astrology and Deepak Chopra, but the book has a more serious project.  Many readers will be aghast at the billions spent on projects the initiators should have known would fail.  Tax dollars squandered on ridiculous projects, as Park describes, are a sobering wake-up.  Park is very informative about the subtle claims where the “official” rules of science are used, such as experimentation and demonstration, but an important piece is missing which no one perceives until the project has failed and the money has been wasted.  This pattern has occurred in such projects as Patterson’s clean energy cells, power lines “causing child cancer,” cold fusion and other frauds.  Our law makers are often lacking in scientific knowledge and are also victims of their own delusions.  Sometimes scientists are fooled.  Park is a splendid writer and Voodoo Science is still an important book.

Park writes a weekly column entitled What’s New for the University of Maryland Website.

Sagan, Carl.  The Demon-Haunted World: Science as a Candle in the Dark. New York: Ballantine Books, 1997.

Sagan’s book remains relevant to readers today.  In a society filled with scientific misinformation and lack of scientific knowledge, Sagan is a breath of fresh air.  He is able to explain, without being condescending, what science does, and why it’s important to our daily lives.  He does a wonderful send-up of UFO’s, crop circles, the Atlantis myth, and other canards.

The late Sagan also debunks fairies, angels, and religious apparitions.  He believes most of the stories of alien abduction and other such fantasies are products of hallucinations, gullibility, and misinformation.  Demon-Haunted World is still read with much pleasure by contemporary secular thinkers.  It has helped people to think critically and to leave the mythology of religion behind.  Sagan even offers his “Baloney Detection Kit” to help readers detect frauds.

Shermer, Michael. Why People Believe Weird Things: Pseudoscience, Superstition, and Other Confusions of our Time. Rev. and Expanded Ed. New York: Henry Holt and Co., 2002.

Michael Shermer is the founding publisher of Skeptic Magazine, Director of the Skeptics Society and monthly columnist for Scientific American.

Weird Things is an extremely popular volume that provides readers with well-written, well thought-out discussions of frauds and foolishness.  But Shermer’s book is much more than an expose.  It is a tribute to science and the scientific method as well.  The first sixty-one pages discuss science and skepticism, explain the scientific method, and discourse on critical thinking. The text provides the reader with the ability to look for problems in statements that purport to be “truth statements” and how to correct one’s problem solving difficulties.

The rest of the volume discusses and dismisses such frauds as near death experiences, alien abductions, witch crazes, the Ayn Rand cult, creationism, Holocaust deniers and more.  He accompanies his work with a few graphs and pictures to punctuate his ideas.  Why do people believe weird things?  Shermer has a few answers: for consolation, for gratification, simplicity, moral meaning and hope. 

Shermer’s style is interesting, clear, plain spoken and witty.  The volume is well-indexed and is accompanied by a fine bibliography.  Weird Things is an excellent guide to thinking clearly and scientifically.

Stephen Greenblatt. The Swerve: How The World Became Modern. Norton, 2011, 356 Pages. $26.95 

The latest issue of the NY Review of Books (Dec. 8, 2011) has a splendid, scholarly article about an equally scholarly book by Stephen Greenblatt about the discovery of a copy of Lucretius’ Nature of Things, the great epicurean masterpiece of the classical world. The book is titled The Swerve: How The World Became Modern. The reviewer is the excellent historian, Anthony Grafton.

Nature of Things was discovered by Poggio, out of a papal job momentarily, because his employer, Pope John XXIII, was arrested and deposed. Poggio began hunting for books in old, dusty monastic libraries. He did not like the monks, suspecting them of corruption and hypocrisy, and they were suspicious of him, too. In 1417, he found the text of Lucretius and from there, this astonishing poem/philosophical treatise helped to further skepticism in the Renaissance scholars who read it.

Greenblatt has performed a wonderful feat of scholarship and also has exposed many readers to the naturalism of the Epicureans. This book is on the best seller list. A great new translation by A.E. Stalling of Lucretius in a new Penguin edition is actually on Amazon’s Best Seller List under Poetry.

This book, The Swerve, is highly recommended in the New York Review of Books, as well as the Stalling translation of Nature of Things.

Books for readers who wish to further their study of Skepticism:

Charles Mackay’s Extraordinary Popular Delusions and Madness of Crowds. (1841); Paul Kurtz. Exuberant Skepticism (2010); Robin M. Dawes. Everyday Irrationality: How Pseudo –Scientists, Lunatics, and the Rest of Us Systematically Fail To Think Rationally. (2003); Kai Nielsen. Skepticism. (1973); Richard Popkin. Skeptical Philosophy for Everyone. (2001.); Leonard Zusne. Anomalistic Psychology: A Study of Magical Thinking, 1990; Benson Mates. The Skeptic’s Way. (1996).

See the Bibliography for all the lectures on Philosophy. There are over 76 works listed.