While I never took debate, I imagine that a lot of these techniques are taught in debate class - whether to recognize them in your opponent (which is good) or to actually use them against your opponent (argh!). A class I did take a long time ago, however, was Logic and Reasoning in my freshman year of college. We talked about all sorts of argument fallacies like ad hominem attacks (where you attack the person rather than their ideas), the straw man, the slippery slope, and one of my real pet peeves, the argument by analogy.

There just aren't many analogy-arguments that hold water. However, they are insanely popular. But when I was talking about this to a friend, I couldn't think of an example. But today I saw Minority Report. Minor spoilers follow.

In the previews it is established that there is a PreCrime Division in Minority Report. They know a murder is about to occur, and they arrest the perpetrator before it happens. There's a critic and they have a discussion that goes something like this:

"You're arresting someone for a crime they didn't commit."

"But they were GOING to commit it."

"But it's a paradox, isn't it? You kept it from occuring, which means it didn't happen, which means the prediction was wrong."

So, one of the characters takes a fragile ball, and rolls it towards the character across a counter. As it rolls off the edge, the critic catches it.

"Why did you catch it?"

"Because it was going to hit the ground."

"But it didn't hit the ground. Do you see? The fact that you stopped it from hitting the ground doesn't change the fact that it was very definitely going to. And you know it was going to."

I watched that scene and it worked for me. It really did feel like a good analogy. Of course, I was distracted by the drama of the movie. But later on I realized it was a perfect example of an analogy fallacy.

ceterus paribus is a latin term that means "other things being equal." That's the requirement one has to meet to structure a logical argument by analogy. This argument with the fragile ball equated the ball's path with destiny - perhaps that is fine. But it also equated the fragile ball with a person. It forced us to accept that the ball had every element in common with a human. And it doesn't.

The key difference I'm driving at here is "choice". Assuming for the sake of argument that there is destiny and future paths - we do know that an object, a ball, has no ability to choose its path. But regardless of whether we believe a person's path is predetermined, we don't know it for certain. The person might be able to choose.

So the person is not the same as the ball. The analogy does not work, and the argument falls apart. It was a fallacy, a flawed argument.