Circumstantial ad hominem, also known as “appeal to motive” and “appeal to personal interest”, is a logical fallacy and one of the different types of ad hominem arguments.
Like other types of ad hominem fallacies, this one also fallaciously focuses on the person behind the argument, rather than on the validity of the argument itself.
Circumstantial ad hominem occurs when someone argues that their opponent’s argument must be invalid because his or her position is predisposed by their personal circumstances.
In other words, this fallacy asserts that someone is arguing as they do only because they have a vested interest in the issue, and thus their argument should be dismissed as false. It’s often characterized by phrases such as: “Of course, that’s what he would say, wouldn’t he”.
As such, this logical fallacy takes typically the following form:
- Person 1 makes an argument X.
- Person 1 has a vested interest in X being true.
- Therefore, X is false.
Here’s a list of several examples to further illustrate this fallacy:
- Kate: Our student council consists mostly of boys so I think it would be good if we get more girls in it and make it more balanced. Jim: You only think that because you are a girl yourself, so your opinion doesn’t matter.
- “Andrew says that raising taxes for the wealthiest would not help the economy. Of course, he is a multimillionaire himself, so his claim must be nonsense as he is just looking out for his own interests.”
- “Of course that priest says he believes in God; as a priest, he is required to say that.”
- A politician argues that the country would be better off if it were to increase spending on education. His opponent, however, points out that this argument should be dismissed entirely since the politician in question would benefit personally from such an increase.
- “You think we should get more women into science? you only say that because you are a woman yourself, so it must be false.”
Why It Is a Fallacy
The circumstantial ad hominem is fallacious specifically because it claims that an argument is necessarily false if there is a conflict of interest between the arguer’s circumstances and the stance they hold.
In reality, this alone is not strong enough evidence to make such an inference: A politician may really hold a certain view even if he were to gain personal advantage from its acceptance, or a salesman can truly believe that the product he is endorsing is the best product in the market.
However, note that in a situation where there is strong evidence for a conflict of interest or enough reasons to believe that the arguer’s position is biased, it may not be unreasonable to point it out.