Skepticism or scepticism (see spelling differences) is generally any questioning attitude towards knowledge, facts, or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere.
Philosophical skepticism is an overall approach that requires all information to be well supported by evidence. Classical philosophical skepticism derives from the 'Skeptikoi', a school who "asserted nothing". Adherents of Pyrrhonism, for instance, suspend judgment in investigations. Skeptics may even doubt the reliability of their own senses. Religious skepticism, on the other hand is "doubt concerning basic religious principles (such as immortality, providence, and revelation)".
- (a) an attitude of doubt or a disposition to incredulity either in general or toward a particular object;
- (b) the doctrine that true knowledge or knowledge in a particular area is uncertain; or
- (c) the method of suspended judgment, systematic doubt, or criticism that is characteristic of skeptics (Merriam–Webster).
In philosophy, scepticism refers more specifically to any one of several propositions. These include propositions about:
- (a) an inquiry,
- (b) a method of obtaining knowledge through systematic doubt and continual testing,
- (c) the arbitrariness, relativity, or subjectivity of moral values,
- (d) the limitations of knowledge,
- (e) a method of intellectual caution and suspended judgment.
Philosophical skepticism 
In philosophical skepticism, pyrrhonism is a position that refrains from making truth claims. A philosophical skeptic does not claim that truth is impossible (which would be a truth claim), instead it recommends "suspending belief". The label is commonly used to describe other philosophies which appear similar to philosophical skepticism, such as academic skepticism, an ancient variant of Platonism that claimed knowledge of truth was impossible. Empiricism is a closely related, but not identical, position to philosophical skepticism. Empiricists see empiricism as a pragmatic compromise between philosophical skepticism and nomothetic science; philosophical skepticism is in turn sometimes referred to as "radical empiricism."
Philosophical skepticism originated in ancient Greek philosophy. The Greek Sophists of the 5th century BCE were for the most part skeptics. Pyrrhonism was a school of skepticism founded by Aenesidemus in the first century BCE and recorded by Sextus Empiricus in the late 2nd century or early 3rd century CE. One of its first proponents was Pyrrho of Elis (c. 360-275 BCE), who traveled and studied as far as India and propounded the adoption of "practical" skepticism. Subsequently, in the "New Academy" Arcesilaus (c. 315-241 BCE) and Carneades (c. 213-129 BCE) developed more theoretical perspectives by which conceptions of absolute truth and falsity were refuted as uncertain. Carneades criticized the views of the Dogmatists, especially supporters of Stoicism, asserting that absolute certainty of knowledge is impossible. Sextus Empiricus (c. CE 200), the main authority for Greek skepticism, developed the position further, incorporating aspects of empiricism into the basis for asserting knowledge.
Greek skeptics criticized the Stoics, accusing them of dogmatism. For the skeptics, the logical mode of argument was untenable, as it relied on propositions which could not be said to be either true or false without relying on further propositions. This was the regress argument, whereby every proposition must rely on other propositions in order to maintain its validity (see the five tropes of Agrippa the Sceptic). In addition, the skeptics argued that two propositions could not rely on each other, as this would create a circular argument (as p implies q and q implies p). For the skeptics, such logic was thus an inadequate measure of truth and could create as many problems as it claimed to have solved. Truth was not, however, necessarily unobtainable, but rather an idea which did not yet exist in a pure form. Although skepticism was accused of denying the possibility of truth, in fact it appears to have mainly been a critical school which merely claimed that logicians had not discovered truth.
In Islamic philosophy, skepticism was established by Al-Ghazali (1058–1111), known in the West as "Algazel", as part of the Ash'ari school of Islamic theology, whose method of skepticism shares many similarities with Descartes' method.
In an effort to avoid skepticism, René Descartes begins his Meditations attempting to find indubitable truth on which to base his knowledge. He later recognizes this truth as "I think, therefore I am," but before he finds this truth, he briefly entertains the skeptical arguments from dreaming and radical deception.
David Hume has also been described as a global skeptic.
Pierre Le Morvan (2011) has distinguished between three broad philosophical approaches to skepticism. The first he calls the "Foil Approach." According to this approach, skepticism is treated as a problem to be solved, or challenge to be met, or threat to be parried; skepticism's value on this view, insofar as it is deemed to have one, accrues from its role as a foil contrastively illuminating what is required for knowledge and justified belief. The second he calls the "Bypass Approach" according to which skepticism is bypassed as a central concern of epistemology. Le Morvan advocates a third approach—he dubs it the "Health Approach"--that explores when skepticism is healthy and when it is not, or when it is virtuous and when it is vicious.
Scientific skepticism 
A scientific (or empirical) skeptic is one who questions beliefs on the basis of scientific understanding. Most scientists, being scientific skeptics, test the reliability of certain kinds of claims by subjecting them to a systematic investigation using some form of the scientific method. As a result, a number of claims are considered "pseudoscience" if they are found to improperly apply or ignore the fundamental aspects of the scientific method. Scientific skepticism may discard beliefs pertaining to things outside perceivable observation and thus outside the realm of systematic, empirical falsifiability/testability.
- Homeopathic Medicine
- Cold Reading
- New Age Medicine
- Magnet Therapy
- Therapeutic touch
Religious skepticism 
Religious skepticism generally refers to doubting given religious beliefs or claims. Historically, religious skepticism can be traced back to Socrates, who doubted many religious claims of the time. Modern religious skepticism typically places more emphasis on scientific and historical methods or evidence, with Michael Shermer writing that it is a process for discovering the truth rather than blanket non-acceptance. For this reason, a religious skeptic may not believe that Jesus existed, or if he did, that he was not the messiah and did not perform miracles. Religious skepticism is not the same as atheism or agnosticism, though these often do involve skeptical attitudes toward religion and philosophical theology (for example, towards divine omnipotence). Religious people are generally skeptical about claims of other religions, at least when the two denominations conflict in some stated belief.
See also 
- Critical thinking
- Debunker, a person who discredits and exposes claims as being false, exaggerated or pretentious.
- Scientific skepticism
Literary skeptics 
- Ambrose Bierce: The Devil's Dictionary
- Ignacy Krasicki: Fables and Parables
- Herman Melville: Moby-Dick, other works
- Montaigne: Essais.
- Bolesław Prus: Pharaoh
- Voltaire: Candide
- Emily Rosa: "A Close Look at Therapeutic Touch," Journal of the American Medical Association, April 1, 1998; 279(13):1005–1010. 
- Australian Skeptics
- Brights movement
- Center for Inquiry
- Committee for Skeptical Inquiry
- New England Skeptical Society
- New Zealand Skeptics
- James Randi Educational Foundation
- Rationalist International
- Skepsis ry (Finnish association of skeptics)
- The Skeptics Society
- Richard Dawkins Foundation for Reason and Science
- The Skeptic's Dictionary
- Skeptical Inquirer
- Skeptic (U.S. magazine)
- The Skeptic (UK magazine)
- The Freethinker (journal)
- The Straight Dope
- Penn & Teller: Bullshit!
- Point of Inquiry
- The Skeptics' Guide to the Universe
- See R. H. Popkin, The History of Skepticism from Erasmus to Descartes (rev. ed. 1968); C. L. Stough, Greek Skepticism (1969); M. Burnyeat, ed., The Skeptical Tradition (1983); B. Stroud, The Significance of Philosophical Skepticism (1984). Encyclopedia2.thefreedictionary.com
- "Philosophical views are typically classed as skeptical when they involve advancing some degree of doubt regarding claims that are elsewhere taken for granted." URM.edu
- "Philosophical skepticism should be distinguished from ordinary skepticism, where doubts are raised against certain beliefs or types of beliefs because the evidence for the particular belief or type of belief is weak or lacking..." Skepdic.com
- Liddell and Scott
- Sextus Empiricus, Outlines Of Pyrrhonism, Translated by R. G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933, p. 21
- "...the two most influential forms of skepticism have, arguably, been the radical epistemological skepticism of the classical Pyrrhonian skeptics and the Cartesian form of radical epistemological skepticism" UTM.edu
- Scepticism – History of Scepticism
- Najm, Sami M. (July–October 1966), "The Place and Function of Doubt in the Philosophies of Descartes and Al-Ghazali", Philosophy East and West (Philosophy East and West, Vol. 16, No. 3/4) 16 (3–4): 133–141, doi:10.2307/1397536, JSTOR 1397536
- Skeptoid.com: What is skepticism?
- A Greek-English Lexicon, Henry George Liddell and Robert Scott, revised and augmented throughout by Sir Henry Stuart Jones, with the assistance of Roderick McKenzie, Clarendon Press, Oxford, UK, 1940. Online, perseus.tufts.edu.
- Richard Hönigswald, Die Skepsis in Philosophie und Wissenschaft, 1914, new edition (ed. and introduction by Christian Benne and Thomas Schirren), Göttingen: Edition Ruprecht, 2008, ISBN 978767530560
- Keeton, Morris T., "skepticism", pp. 277–278 in Dagobert D. Runes (ed.), Dictionary of Philosophy, Littlefield, Adams, and Company, Totowa, NJ, 1962.
- Le Morvan, P., "Healthy Skepticism and Practical Wisdom," Logos & Episteme II, 1 (2011): 87-102. <http://logos-and-episteme.proiectsbc.ro/sites/default/files/HEALTHY%20SKEPTICISM%20AND%20PRACTICAL%20WISDOM.pdf>
- Runes, D.D. (ed.), Dictionary of Philosophy, Littlefield, Adams, and Company, Totowa, NJ, 1962.
- Webster's New International Dictionary of the English Language, Second Edition, Unabridged, W.A. Neilson, T.A. Knott, P.W. Carhart (eds.), G. & C. Merriam Company, Springfield, MA, 1950.
- Butchvarov, Panayot, Skepticism About the External World (Oxford University Press, 1998).
- Daniels, M.D., D.; Price, PhD, V. (2000), The Essential Enneagram, New York: HarperCollins
Further reading 
- Sextus Empiricus, Outlines of Pyrrhonism, R.G. Bury (trans.), Prometheus Books, Buffalo, NY, 1990.
- Richard Wilson, Don't Get Fooled Again - The skeptic's guide to life, Icon Books, London, 2008. ISBN 978-1-84831-014-8
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- Skepticism at PhilPapers
- Skepticism at the Indiana Philosophy Ontology Project
- Skepticism entry in the Stanford Encyclopedia of Philosophy
- Contemporary skepticism entry in the Internet Encyclopedia of Philosophy
- Ancient Greek skepticism entry in the Internet Encyclopedia of Philosophy
- Skeptical theism entry in the Internet Encyclopedia of Philosophy
- Skeptical Inquiry at the Open Directory Project
- "Most Scientific Papers are Probably Wrong", NewScientist, 30 August 2005
- "In the Name of Skepticism: Martin Gardner's Misrepresentations of General Semantics", by Bruce I. Kodish, appeared in General Semantics Bulletin, Number 71, 2004.
- Classical Skepticism by Peter Suber
- "Outstanding skeptics of the 20th century" – Skeptical Inquirer magazine
- "CSICOP and the Skeptics" – critical essay by paranormal believer George P. Hansen
- "Nonsense (And Why It's So Popular)" – course syllabus from The College of Wooster.
- "Scepticism". Catholic Encyclopedia. New York: Robert Appleton Company. 1913. – A Christian (Catholic) account of scepticism
- Media Guide to Skepticism - Doubtful News