Editing Confirmation bias (section)

=== Informal observations ===
[[File:Somer Francis Bacon.jpg|thumb|upright|alt=Engraved head-and-shoulders portrait of Francis Bacon wearing a hat and ruff.|[[Francis Bacon]]]]
Before psychological research on confirmation bias, the phenomenon had been observed throughout history. Beginning with the Greek historian [[Thucydides]] ({{circa|460&nbsp;BC}}&nbsp;– {{circa|395&nbsp;BC}}), who wrote of misguided reason in ''[[History of the Peloponnesian War|The Peloponnesian War]]''; "...&nbsp;for it is a habit of mankind to entrust to careless hope what they long for, and to use sovereign reason to thrust aside what they do not fancy".<ref>{{Thucydides|en|4|108|4|shortref}}.</ref> Italian poet [[Dante Alighieri]] (1265–1321) noted it in the ''[[Divine Comedy]]'', in which [[St. Thomas Aquinas]] cautions Dante upon meeting in Paradise, "opinion—hasty—often can incline to the wrong side, and then affection for one's own opinion binds, confines the mind".<ref>Alighieri, Dante. ''Paradiso'' canto XIII: 118–120. Trans. Allen Mandelbaum.</ref> [[Ibn Khaldun]] noticed the same effect in his ''[[Muqaddimah]]'':<ref>{{Citation |title=The Muqadimmah |author=Ibn Khaldun |publisher=[[Princeton University Press]] |location=Princeton, NJ |year=1958 |page=71}}.</ref>
{{blockquote|Untruth naturally afflicts historical information. There are various reasons that make this unavoidable. One of them is partisanship for opinions and schools. ... if the soul is infected with partisanship for a particular opinion or sect, it accepts without a moment's hesitation the information that is agreeable to it. Prejudice and partisanship obscure the critical faculty and preclude critical investigation. The result is that falsehoods are accepted and transmitted.}} In the ''[[Novum Organum]]'', English philosopher and scientist [[Francis Bacon]] (1561–1626)<ref name="baron195">{{Harvnb|Baron|2000|pp=195–196}}.</ref> noted that biased assessment of evidence drove "all superstitions, whether in astrology, dreams, omens, divine judgments or the like".<ref name="bacon">Bacon, Francis (1620). ''Novum Organum''. reprinted in {{Citation |title=The English philosophers from Bacon to Mill |editor-first=E.&nbsp;A. |editor-last=Burtt |publisher=[[Random House]] |location=New York |year=1939 |page=36}} via {{Harvnb|Nickerson|1998|p=176}}.</ref> He wrote:<ref name="bacon"/>
{{blockquote|The human understanding when it has once adopted an opinion&nbsp;...<!--"(either as being the received opinion or as being agreeable to itself)" omitted for space--> draws all things else to support and agree with it. And though there be a greater number and weight of instances to be found on the other side, yet these it either neglects or despises, or else by some distinction sets aside or rejects[.]}}
In the second volume of his ''[[The World as Will and Representation]]'' (1844), German philosopher [[Arthur Schopenhauer]] observed that "An adopted hypothesis gives us lynx-eyes for everything that confirms it and makes us blind to everything that contradicts it."<ref>{{Citation|last=Schopenhauer |first=Arthur |title=''The World as Will and Presentation'' |volume=2 |editor1-first=David |editor1-last=Carus |editor2-first=Richard E. |editor2-last=Aquila |location=New York |publisher=[[Routledge]] |year=2011 |orig-year=1844 |page=246}}.</ref>

In his essay (1897) ''[[What Is Art?]]'', Russian novelist [[Leo Tolstoy]] wrote:<ref name=":1">Tolstoy, Leo (1896). ''What Is Art?'' ch. 14 [https://www.gutenberg.org/files/43302/43302-h/43302-h.htm p. 143] {{Webarchive|url=https://web.archive.org/web/20210817153200/https://www.gutenberg.org/files/43302/43302-h/43302-h.htm |date=17 August 2021 }}. Translated from Russian by Aylmer Maude, New York, 1904. [https://www.gutenberg.org/files/64908/64908-h/64908-h.htm Project Gutenberg edition] {{Webarchive|url=https://web.archive.org/web/20210807151038/https://www.gutenberg.org/files/64908/64908-h/64908-h.htm |date=7 August 2021 }} released 23 March 2021. Retrieved 17 August 2021.</ref>
{{blockquote|I know that most men—not only those considered clever, but even those who are very clever, and capable of understanding most difficult scientific, mathematical, or philosophic problems—can very seldom discern even the simplest and most obvious truth if it be such as to oblige them to admit the falsity of conclusions they have formed, perhaps with much difficulty—conclusions of which they are proud, which they have taught to others, and on which they have built their lives.}} In his essay (1894) ''[[The Kingdom of God Is Within You]]'', Tolstoy had earlier written:<ref name=":2">Tolstoy, Leo (1894). ''The Kingdom of God Is Within You'' [https://www.gutenberg.org/files/43302/43302-h/43302-h.htm p. 49] {{Webarchive|url=https://web.archive.org/web/20210817153200/https://www.gutenberg.org/files/43302/43302-h/43302-h.htm |date=17 August 2021 }}. Translated from Russian by Constance Garnett, New York, 1894. [https://www.gutenberg.org/files/43302/43302-h/43302-h.htm Project Gutenberg edition] {{Webarchive|url=https://web.archive.org/web/20210817153200/https://www.gutenberg.org/files/43302/43302-h/43302-h.htm |date=17 August 2021 }} released 26 July 2013. Retrieved 17 August 2021.</ref>
{{Blockquote|text=The most difficult subjects can be explained to the most slow-witted man if he has not formed any idea of them already; but the simplest thing cannot be made clear to the most intelligent man if he is firmly persuaded that he knows already, without a shadow of doubt, what is laid before him.|author=|title=|source=}}