1. Consensus as agreement

S. Agreement; Persuasion

2 Argument from consensus

The label argument from consensus, appeal to consensus, covers a family of arguments claiming that a belief is true or that things must be done in such and such a way on the basis that everybody thinks or does this, and that other proposals should be rejected. It implies that by flouting the existing consensus, the proponent of a new measure, that is the opponent to consensus, is on the verge of being excluded from this community, S. Burden of proof. These arguments have the general form:

We always thought, desired, did … like that; so buy (please, do…) like that.
Everybody loves the product So-and-So.
Everybody puts Such and Such ketchup on their burger!

The universal consensus argument claims that “all men in all times have thought so and things have always been done that way”. The existence of God has been argued upon the universal consensus argument.

The argument from the relative (partial) consensus covers the argument from majority, the argument from number (Lat. ad numerum; numerus, “number”) and related expressions:

The majority / many people … think, desire, do … X.
Three million Syldavians have already adopted it!
My book sold better than yours.
He is a well-known actor.

Common Sense — The argument of consensus includes the kind of authority generously granted to traditional wisdom or to common sense, S. Authority.

I know that all true Syldavians approve of this decision
Only extremes attack me, all people of common sense will agree with me.

Populist argument is based on a kind of consensus among the people (or attributed to it), S. Ad Populum.

Bandwagon argument and fallacy — The bandwagon argument is a special case of the argument from consensus about an action. The bandwagon being the decorated wagon that leads the orchestra through the city, the bandwagon argument adds joy and enthusiasm to the dry argument from consensus. To climb on the bandwagon is to follow the popular movement, to share in a popular “emotion” in the etymological sense, “a public upheaval”. Joining a party to have fun and sing should not be condemned as systematically fallacious; but, seen by any opposing party, climbing on the bandwagon can be considered as fallacious, as a follow-the-group or follow-my-leader attitude, sheepish behavior, uncritically adopting the views of the most vocal or visible group.