The proof by repetition is sometimes metonymically designated under the Latin name of its effect, arg. ad nauseam, Lat. nausea “nausea, disgust”.

Any meaningful or pragmatically relevant segment can be repeated for a variety of purposes: something may be repeated because it has not been clearly heard or understood; the second speaker may repeat the end of the first turn to link it with his or her second turn, etc. Repetition may consist in repeating an initial phrase or speech act word for word, as is the case in formal quotations. Alternatively, repetition might slightly reformulate something which can be heard everywhere, as a well-known argumentation borrowed from a script. Conscious, strategic repetition of slightly modulated core contents is the key of traditional methods in education; repetition of the same action is the basis of learning-by-doing.

While most repetitions are unplanned and remain unnoticed, the argument by repetition or proof by repeated assertion is part of a strategy to impose on people a unilateral, uncritical vision of things. The focus is put upon a single key statement, presented not as a claim but as an obvious necessary truth, repetition creating a feeling of self-evidence.

Although called “argument”, this process is characterized by the absence of argument. It offers no reason, good or bad, to support the claim; reasons are not implied or contextually retrievable but are carefully ignored. Such strategic repetition can therefore be considered to be argumentative only if an argument is defined by its effect, persuasion. Repetition is instrumental to persuasion, which could itself be seen as a disposition, or a readiness to repeat under appropriate circumstances. Note that repeating a whole complex argument results in an argument by repetition rather than any other kind of argument: “we will win because we are the strongest”.

The sociologist Gustave Le Bon emphasized the power of repetition to gain people’s assent:

Pure and simple assertion [affirmation], kept free of all reasoning and all proof, is one of the surest means of making an idea enter the mind of crowds […]
Affirmation, however, has no real influence unless it be constantly repeated, and so far as possible in the same terms. It was Napoleon, I believe, who said that there is only one figure in rhetoric of serious importance, namely, repetition. The thing affirmed comes by repetition to fix itself in the mind in such a way that it is accepted in the end as a demonstrated truth. […]
To this circumstance is due the astonishing power of advertisements. When we have read a hundred, a thousand times that X’s chocolate is the best, we imagine we have heard it said in many quarters, and we end by acquiring the certitude that such is the fact. (Le Bon [1895], p. 126-127)

This last remark shows that repetition produces an illusion of legitimation by the authority of great number, S. Consensus.

From the point of view of the evaluation of arguments, this form of repetition is regarded as a fallacy, and even as the fallacy par excellence, since it imposes the acceptance of a statement not only without justification but against all justification.