Entry in progress—B.P.
   
Wiktionary
conventional wisdom (plural conventional wisdoms)
A belief or set of beliefs that is widely accepted, especially one which may be questionable on close examination.
 
1958, John Kenneth Galbraith, The Affluent Society,
It will be convenient to have a name for the ideas which are esteemed at any time for their acceptability, and it should be a term that emphasizes this predictability. I shall refer to these ideas henceforth as the conventional wisdom.
1971, “Week’s Watch,” Time, 17 May,
So many Americans accept “zero population growth” as a new canon of conventional wisdom that it comes as a surprise to hear the notion disputed.
 
Wikipedia: Conventional wisdom
Conventional wisdom (CW) is a term used to describe ideas or explanations that are generally accepted as true by the public or by experts in a field. The term implies that the ideas or explanations, though widely held, are unexamined and, hence, may be reevaluated upon further examination or as events unfold.
 
The term is often credited to the economist John Kenneth Galbraith, who used it in his 1958 book The Affluent Society:
 
It will be convenient to have a name for the ideas which are esteemed at any time for their acceptability, and it should be a term that emphasizes this predictability. I shall refer to these ideas henceforth as the conventional wisdom.
 
The term in actuality is much older and dates at least to 1838. “Conventional wisdom” was used in a number of other works prior to Galbraith, occasionally in a positive or neutral sense, but more often pejoratively.
 
Conventional wisdom is not necessarily true. Conventional wisdom is additionally often seen as an obstacle to introducing new theories, explanations, and so as an obstacle that must be overcome by such revisionism. This is to say, that despite new information to the contrary, conventional wisdom has a property analogous to inertia that opposes the introduction of contrary belief, sometimes to the point of absurd denial of the new information set by persons strongly holding an outdated (conventional wisdom) view. This inertia is due to conventional wisdom being made of ideas that are convenient, appealing and deeply assumed by the public, who hangs on to them even as they grow outdated. The unavoidable outcome is these ideas will eventually not match reality at all, so conventional wisdom will be violently shaken until it doesn’t conflict reality so blatantly.
 
The concept of conventional wisdom also is applied or implied in political senses, often related closely with the phenomenon of talking points. It is used pejoratively to refer to the idea that statements which are repeated over and over become conventional wisdom regardless of whether or not they are true.
 
In a more general sense, it is used to refer to the accepted truth about something which nearly no-one would argue about, and so is used as a gauge (or well-spring) of normative behavior or belief, even within a professional context. One such example was conventional wisdom in 1960, even among most doctors, dictated that smoking was not particularly harmful to one’s health. Another: It might be used in this manner discussing a technical matter such as the conventional wisdom was that a man would suffer fatal injuries if he experienced more than eighteen g-forces in an aerospace vehicle. (John Stapp shattered that myth by repeatedly withstanding far more in his research—peaking above 46 Gs).
 
Conventional wisdom may itself be the subject of legends. For example, it is widely believed that conventional wisdom prior to Christopher Columbus held that the world was flat, when in actuality scholars had long accepted that the earth is a sphere.
 
When conventional wisdoms are overthrown, outranked, or outflanked by new ideas, and the new conventional wisdom becomes established in place of the previous one, there may yet be considerable remaining affiliation to the previous regime.
 
Merriam Webster’s Online Dictionary
Main Entry: conventional wisdom
Function: noun
Date: 1850
: the generally accepted belief, opinion, judgment, or prediction about a particular matter
 
Google Books
An inquiry into the moral and religious character of the American government
By H W Warner and Theodore Frelinghuysen
New York, NY: Wiley and Putnam
1838
Pg. 35:
...and it will be seen that we appeal in such a case, neither to the records of legilsation, nor yet to the conventional wisdom of our forefathers;...
 
10 January 1845, Daily National Intelligencer (Washington, DC), “The Secret of Scotch Banking,” pg. 2:
In this way overtrading, in so far as regards the issue of paper, is so effectually guarded and conrolled, that it would puzzle Parliament, with all its conceded convetional wisdom, to devise any plan alike so simple and expeditious.—Blackwood.