Asserting that something is so because 'everybody thinks it is so'.
As they say:
"One thousand lemmings can't be wrong."
Examples:
The Earth is flat ... (because everybody thinks so)
Terrorists are behind 9/11
The Earth is round ... (because everybody thinks so... hmmmm.....)
Not to be confused with the more reasonable practice of insisting that words should, in general, be allowed to stand for their "usual" meanings.
Discussion
Some camps consider this a valid justification for a particular definition. Another camp disagrees and cites the Scientific Method as its preferred justification criteria.
Both camps agree that "a definition of a term is correct if it accurately represents the concept the term is associated with" and "a concept is justified if it is useful".
The title could also be Argumentum Ad Populum or Appeal To Popularity or Argument From The Masses.
Classic Blackadder...
Old Sea Captain: "Crew, m'lord?"
Blackadder: "A crew, yes, a crew! I thought it was customary to have a crew when one sets sail for the deep south."
Old Sea Captain: "Opinion on the matter is divided, m'lord. All the other sea captains say it is. I say it isn't."
... a fallacious argument can have a true conclusion. See Disproof By Fallacy, which is itself a fallacy. However, combined with Occams Razor and the Scientific Method, it is enough to show that X has not been proven.
Is there a more "mild" version of this for popularity among experts? Example, "Most scientists think cow farts cause warts. Thus, it must be true". Most don't consider scientists "masses" (at least not until globalization creates a billion of them).
It might be an extreme form of Argument From Authority; then again appeals to "most" of anything seldom have anything resembling a survey of the group being referenced, in support of the proposition that "most" agree. As a practical example, many commercials for medicine like to quote the omnipresent "three out of four doctors"--which often means "three out of the four doctors who work for us that were asked the question". Proper citation from authority will reference actual studies or works published under the aegis of recognized scientific bodies*; not just drop the names of particular scientists or unverifieable samples of anonymous scientists.
Many scientific disciplines, as well as professional disciplines that aren't scientific in nature (ie accounting and law), have professional bodies that represent the discipline as a whole. For example, IEEE, ACM, FASB (Financial Accounting Standards Board), the AMA (American Medical Association), the ABA (American Bar Association) and state bars, etc. In some cases, these organizations have legal standing to speak for and regulate the discipline (ie FASB and ABA); in other cases they command respect among practitioners but have no legal weight. Many such organizations will issue pronouncements regarding the current state of the discipline and the knowledge it has accumulated; reputable professional bodies generally won't issue such pronouncements unless there is broad agreement among the scientific community. Citing such opinions/pronouncements is probably not a logical fallacy.
Many of them are conventions necessary for consistency. Accounting comes to mind. Stocks could not be reported in an apples-to-apples way if not for the consistency rules. Same with computer language standards: no cross-machine run ability without consistency. However, the existence of a convention/protocol is not the same as "proving it the best".
Also, often "best practices" are merely a technique to avoid getting sued. "I followed accepted practices, and thus should not be sued for following them." The reasons for agreements are often social, not scientific.
See original on c2.com 