Appeal to motive is a pattern of argument which consists in challenging a thesis by calling into question the motives of its proposer. It can be considered as a special case of the ad hominem circumstantial argument. As such, this type of argument may be a logical fallacy.

Examples

• "That website recommended nVidia's graphics chip over ATI's. But they also display nVidia advertising on their site, so they were probably biased in their review." The thesis in this case is the website's evaluation of the relative merits of the two chips.

• "The only reason why she got the part in that movie is because her husband is the director." In this case, the thesis is less clear, but could be an assertion that the husband made in regard to his wife's acting ability.

• "The referee comes from the same place as (a sports team), so his refereeing was obviously biased towards them." In this case, the thesis consists of the referee's rulings.

A common occurrence in appeals to motive is that only the possibility of a motive (however small) is shown, without showing the motive actually existed. Indeed, it is often assumed that the mere possibility of motive is evidence enough.