I. Definition

Are you skeptical about holistic medicine? Climate change? The existence of extra-terrestrials? We’ve come to use the word “skepticism,” in our society, most often, to express doubt in new or “far out” ideas.  Originally, in ancient Greece, skepticism was the philosophy of questioning all claims, religious, ethical, scientific, or otherwise.  The point of skepticism was not so much to disbelieve claims, but to interrogate them; the word skepticism is derived from the Greek skepsis, meaning “inquiry.”

Philosophical skepticism can mean either:

  • questioning all claims, perhaps in order to better ascertain the truth, or . . .
  • the belief that there are no certain truths (including that statement itself) — no knowledge, only beliefs.

In practice, skeptics don’t always distinguish between these two attitudes, simply questioning claims, without worrying about whether absolute truth is possible.

More specific kinds of skepticism include religious skepticism, moral skepticism, legal skepticism, and scientific skepticism (see section five for details).

Skepticism is not the same as agnosticism, atheism, or faith in the current scientific model of nature, although it overlaps with all these attitudes.  The true skeptic questions all beliefs including current scientific theories.  However, skepticism is inherently associated with science because questioning and demanding proof is part of the scientific method.


II. The History of Skepticism

In the western tradition, skepticism is generally credited to the Greek philosopher Pyrrhus, from around 350 B.C.E–although the Sophists before him also promoted skeptical attitudes.  It’s known that Pyrrhus traveled to India and communicated with “gymnosophists” a Greek term meaning “naked lovers of knowledge”; these were probably Hindu ascetics of some kind, many of whom lived literally naked and homeless, devoting their time to the development of mystical knowledge through meditation.  Hinduism is not, in general, a highly skeptical belief system, with its faith in gods and transcendental reality, but it developed philosophical schools of thought that questioned the possibility of truth; and, Pyrrhus was particularly convinced by the Indians not to trust the evidence of the five senses.

It may not be inconsistent with Pyrrhus’s skepticism that his Hindu colleagues had spiritual beliefs; Pyrrhus and his students focused on the value of questioning rather than on disbelief.  They argued most, in ancient Greece, with the Stoics, who had dogmatic beliefs about morality and the purpose of life.  Otherwise, skepticism seems to be assumed by most other Greek philosophies (except Stoicism); Socrates, Plato, Aristotle, and many others practiced skepticism, whether they considered themselves Pyrrhonists or not.

The medieval domination of Europe by dogmatic Catholicism put a relative end to public expressions of skepticism in the west for about 1,000 years; the Church was supposed to be an authoritative source of truth and to question its dictates could be heresy.

Skepticism flowered again with the Enlightenment and the Age of Reason, and has remained a central—perhaps the most central–aspect of philosophy and science ever since then. So much so that the word skepticism has come to mean “believing in science” to many people, causing some confusion.  Now, many people who call themselves “skeptics” not only question, but simply deny, the truth of any idea not already supported by their current beliefs, scientific or otherwise.  But that contradicts the real philosophy of skepticism, which implies questioning all your beliefs, not just the ones you don’t like, and remaining open to new ideas.

III. Controversies

Can anything be known? Nearly everyone agrees that inquiry is valuable in the quest for knowledge.  But more radical forms of skepticism claim that there can be no certainty.  Since figuring out truths is the central task of philosophy, many philosophers have struggled to determine what can and cannot be known, or to create a method for arriving at undoubtable truths. There are quite a few famous arguments and thought experiments with these goals:

  • Renee Descarte’s cogito ergo sum “I think therefore I am” was intended to answer the question, “What can I not doubt?” It is an appealing answer, however, various philosophies still question whether “I am.”
  • The brain-in-a-vat: Imagine that you could be a brain in a vat, being fed a simulation of reality, much as in the Matrix films’ this is a “thought experiment” intended to show that one can doubt everything about external reality. Other thought-experiments carry the same message:
    • The dream argument (that you could always be dreaming)
    • The fake memory argument (you could have been created and put in this fake reality five minutes ago, with fake memories)
  • The phenomenological reduction: introduced by Edmund Husserl, this is the act of accepting as true only that one is perceiving or experiencing something, neither believing nor dis-believing the reality of those perceptions.

Thus, many philosophers agree that it’s impossible to know anything about external reality for sure.  Yet, at the same time, most believe that, practically speaking, reliable knowledge comes from two sources—empirical observation and rational thought—especially logic.  Most philosophers believe that logic, ideally, is not vulnerable to the brain-in-the vat argument.  Living in a hallucinatory reality wouldn’t change the laws of logic—or math.  And although all empirical observations could be hallucinatory, few philosophers consider that a good reason to especially doubt the natural laws derived by science; they have proven themselves reliable.  But, in the final analysis, a good skeptic will always be ready to question them again.

Several perspectives that became well-known in our society since the 1950s question things that westerner philosophers have thought unquestionable.  Many varieties of eastern mysticism maintain that if one meditates correctly, one will discover that the “I am” is merely an idea, not a reality.  And Taoism, modern linguistic science, and post-modern philosophy all question the ability of logic to express truth, arguing that all symbols are inherently limited, incapable of representing reality truly.  So, although philosophers and scientists continue to rely on logic and observation, radical, complete, skepticism remains a viable philosophy.


IV. Famous Quotes about Skepticism

Quotation #1

“Extraordinary claims require extraordinary evidence.” ― Carl Sagan

Practically the mantra of modern scientific skepticism, Sagan’s pithy motto is taken to justify both the extremely stringent standards of proof in professional science, and the practice of requiring even more proof for truly extraordinary claims, such as ESP, even when a fair amount of evidence is reported.  Sagan’s statement appeals to skeptics but it should be questioned (of course); is it really logical to require a higher standard of proof for any one claim as opposed to another? One could argue that Sagan’s statement implies unreasonable faith in ‘ordinary claims’!

Quotation #2

“She believed in nothing. Only her skepticism kept her from being an atheist.”
― Jean-Paul Sartre

Sartre’s quip cuts to the heart of the problem with regarding skepticism as an allegiance with science against beliefs in the supernatural.  Radical skepticism, which could be interpreted as believing in nothing, dictates that one should question all beliefs, including those that deny the supernatural.


V. Types of Skepticism

  • Philosophical skepticism: We’ve talked about this one already; let’s distinguish its sub-types:
  • Pyrrhonic skepticism promotes questioning, as a method for better approaching truth, but does not deny the possibility of knowledge.
  • Academic skepticism denies the possibility of knowledge.
  • Global skepticism applies to all knowledge.
  • Local skepticism applies to a particular area of knowledge.
  • Moral skepticism is skepticism about moral truths
  • Religious skepticism is skepticism about religious beliefs
  • Metaphysical skepticism claims it’s impossible to know the ultimate nature of reality.
  • Scientific skepticism says that claims of truth about reality should be subjected to the scientific method and its requirements for proof.

VI. Skepticism versus Pessimism

Pessimism is the expectation that things will go badly.  Skepticism is often used in everyday language to mean “pessimism”; a person can say, “I am skeptical about the outcome,” meaning that they question the likelihood of a positive outcome.  This is confusing because skepticism and pessimism really have little in common. Pessimism is a belief in negative outcomes.  While skepticism not a belief in anything and is neither positive nor negative, unless you feel that questioning is inherently negative.

VII.  Skepticism in Popular Culture

Example #1

Contact, the film

In this film based on a novel by Carl Sagan, Jodie Foster’s character, a scientist and atheist, finds herself in the odd position of believing in an extraordinary experience—contact with extra-terrestrials—without proof.  In this scene, her critics use the same arguments against her, that she has always made against belief in God, which is why she glances over at her boyfriend the preacher.  As a good scientist, she cedes the argument to the skeptics, but her final speech suggests a valuable criticism of skepticism—that there may be unprovable truths.

Example #2

The problem of fake news and the reliability of internet sources

Basically, the solution to these problems is skepticism.  The problem is that more and more people take whatever they read online without skepticism.  Or are skeptical about only the things they already disagree with.  The original Greek meaning of skepticism, inquiry, is the solution to this problem; knowledge depends on questioning.  On the internet, this includes fact-checking and investigating the reliability of sources and alternative points of view.


Which of the following embodies the original meaning of skepticism?





What cannot be doubted, by even the most radical skeptic?





Which kind of skepticism denies the possibility of knowledge?





In which of the following does skepticism mean “believing that something is wrong”?





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