People sometimes argue in the following way:
- Person X claims that we shouldn’t do act Y.
- But Person X does Y.
- Therefore, Person X is wrong to claim that we shouldn’t do Y.
This is a fallacy. It doesn’t follow that because a person prescribes one thing but doesn’t do that thing that the person is wrong to claim that we should do that thing (or that doing that thing is wrong). Features about a person’s behaviour have nothing to do with the truth of the views that person holds, and the truth of a view is unconnected to how any one person acts. The name for this general type of fallacy is an ad hominem because it attacks the person instead of the view. Given that the person has nothing to do with the truth of the view, it’s a logical error to connect them.1
Leonardo DiCaprio won the Oscar for best actor recently. In his acceptance speech he advocated for environmentalism, as he did following his visit to Alberta during filming for The Revenant. Lately I’ve been seeing our argument in the following form, so much so that I’ve dubbed it the ‘Anti-Leo Fallacy’:
- Leonardo DiCaprio claims that we shouldn’t use fossil fuels.
- But Leo uses fossil fuels.
- Therefore, Leo is wrong to claim that we shouldn’t use fossil fuels.
Albertans with pro-oil leanings have been using this argument with such frequency that I won’t be surprised if some legislator attempts to make it Alberta’s new motto. But just as with the generic form of the argument, it’s simply an error to conclude that using oil is bad or good based on how Leonardo DiCaprio acts (get it?).
But surely there’s something wrong about Leo telling us how to act when he doesn’t practice what he preaches. Perhaps there is. But that makes him a hypocrite, not wrong (or right).1. Jeremy Davis reminded me that the name for this specific type of ad hominem is the ‘tu quoque fallacy’.