Argument from authority
An argument from authority (Latin: argumentum ad verecundiam), also called an appeal to authority, is a logical fallacy that argues that a position is true or more likely to be true because an authority or authorities agree with it.
Carl Sagan wrote of arguments from authority:
"One of the great commandments of science is, 'Mistrust arguments from authority.'...Too many such arguments have proved too painfully wrong. Authorities must prove their contentions like everybody else." 
Historically, opinion on the appeal to authority has been divided - it has been held to be a valid argument about as often as it has been considered an outright fallacy.
John Locke, in his 1690 Essay Concerning Human Understanding, was the first to identify argumentum ad verecundiam as a specific category of argument. Although he did not call this type of argument a fallacy, he did note that it can be misused by taking advantage of the "respect" and "submission" of the reader or listener to persuade them to accept the conclusion. Over time, logic textbooks started to adopt and change Locke's original terminology to refer more specifically to fallacious uses of the argument from authority. By the mid-twentieth century, it was common for logic textbooks to refer to the "Fallacy of appealing to authority," even while noting that "this method of argument is not always strictly fallacious."
More recently, logic textbooks have shifted to a less blanket approach to these arguments, now often referring to the fallacy as the "Argument from Unqualified Authority" or the "Argument from Unreliable Authority".
Fallacious arguments from authority can also be the result of citing a non-authority as an authority. These arguments assume that a person without status or authority is inherently reliable. The appeal to poverty for example is the fallacy of thinking a conclusion is more likely to be correct because the one who holds or is presenting it is poor. When an argument holds that a conclusion is likely to be true precisely because the one who holds or is presenting it lacks authority, it is a fallacious appeal to the common man. A common example of the fallacy is appealing to an authority in one subject to pontificate on another - for example citing Albert Einstein as an authority on religion when his expertise was in physics.
However, it is also a fallacious ad hominem argument to argue that a person presenting statements lacks authority and thus their arguments do not need to be considered. As appeals to a perceived lack of authority, these types of argument are fallacious for much the same reasons as an appeal to authority.
Inaccurate chromosome number
In 1923, leading American zoologist Theophilus Painter declared, based on poor data and conflicting observations he had made, that humans had 24 pairs of chromosomes. From the 1920s to the 1950s, this continued to be held based on Painter's authority, despite subsequent counts totaling the correct number of 23. Even textbooks with photos clearly showing 23 pairs incorrectly declared the number to be 24 based on the authority of the then-consensus of 24 pairs.
This seemingly established number created confirmation bias among researchers, and "most cytologists, expecting to detect Painter's number, virtually always did so". Painter's "influence was so great that many scientists preferred to believe his count over the actual evidence", to the point that "textbooks from the time carried photographs showing twenty-three pairs of chromosomes, and yet the caption would say there were twenty-four". Scientists who obtained the accurate number modified or discarded their data to agree with Painter's count.
An integral part of the appeal to authority is the cognitive bias known as the Asch effect. In repeated and modified instances of the Asch conformity experiments, it was found that high-status individuals create a stronger likelihood of a subject agreeing with an obviously false conclusion, despite the subject normally being able to clearly see that the answer was incorrect.
Further, humans have been shown to feel strong emotional pressure to conform to authorities and majority positions. A repeat of the experiments by another group of researchers found that "Participants reported considerable distress under the group pressure", with 59% conforming at least once and agreeing with the clearly incorrect answer, whereas the incorrect answer was much more rarely given when no such pressures were present.
Scholars have noted that the academic environment produces a nearly ideal situation for these processes to take hold, and they can affect entire academic disciplines, giving rise to groupthink. One paper about the philosophy of mathematics for example notes that, within mathematics,
"If...a person accepts our discipline, and goes through two or three years of graduate study in mathematics, he absorbs our way of thinking, and is no longer the critical outsider he once was...If the student is unable to absorb our way of thinking, we flunk him out, of course. If he gets through our obstacle course and then decides that our arguments are unclear or incorrect, we dismiss him as a crank, crackpot, or misfit." 
- Ipse dixit
- Informal fallacy
- Manifesto of the Ninety-Three
- Woozle Effect
- Philosophical problems of testimony
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- David, Phillip J.; Hersh, Reuben (1998). New Directions in the Philosophy of Mathematics (PDF). Princeton University Press. p. 8.
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- The dictionary definition of ad verecundiam at Wiktionary