A couple days ago I reviewed three logical fallacies that had come up with unusual frequency in my life over the preceding weeks. I wanted to add a few to the list.
An argument from authority (argumentum ad verecundiam) relies on the source's reputation rather than on evidence relevant to the argument:
- "Mike Ditka recommends this product, so I should buy it too." (Mike Ditka knows a lot about how to coach a football team, but there is no evidence that he has any particular expertise around the product he's endorsing.)
- "This class is valuable because business leaders believe it's valuable." (Even if the business leaders in question have specific knowledge about the class and may even have evidence that, in general, it's useful, they may not have information about you that obviates the class or renders it less valuable.)
- "The President eats pork rinds, so they must be good for you.” (The speaker presents evidence only of the President's snack choices, not that pork rinds have any value in themselves.)
Also common is the (correct definition of) begging the question (petitio principii), in which an argument relies on itself instead of evidence:
Moe: "I always vote wisely."
Moe: "Because I always vote Republican."
Joe: "Why is voting Republican the wiser choice?"
Moe: "Because it just is."
Finally, the classic material fallacy of after this, therefore because of this (post hoc ergo propter hoc, also known as "correlation is not causation"):
- "I know that breaking a mirror brings bad luck, because my cousin broke a mirror one day and had a car accident the next." (There is no clear causal chain between the events; they are essentially random.)
- Superstitions are often manifestations of this fallacy.
The teaching materials I put together back in the day got a little more advanced, but I'm proud to report that the juniors and seniors who went through the lessons understood it and were able to apply it to the rest of the history class I assisted with. I may post more of them in the next few days.