The word “fallacy” has come up here and there throughout the lessons up until now, and now, we’re going to dive into them headfirst. Often times, fallacies will pop up in our regular discourse, and we won’t even recognize them. That is why this course will take a very close look at logical fallacies, examining a number of the more common ones, breaking them down, and showing why they are fallacious. Watch out for all of these user-defined business logic fallacies in your everyday life, whether it’s a calm debate with a friend or the foundation of your belief system.

Formal vs. Informal Fallacies

As you know, formal means relating to the form of an argument, so all of the fallacies that we are about to examine will be fallacies that are derived from an argument’s form.

Affirming the Consequent
If A, B; B, therefore A

Affirming the consequent is when you put the cart before the horse, as it were. It deals with sets of two that are causal, as in, one leads to the other. When you turn it around, implying that the effect also would cause the cause, so to speak, it is an invalid argument. For a rather stark example: If Steve gets shot, Steve will die. Steve died, therefore, Steve was shot. In a more familiar, less obviously false example: If that bureau/business is inefficient, it will fail. It failed, therefore, it was inefficient. It’s a commonly used tactic in terms of discrediting anything that the arguer wants to paint in a poor light. There are a number of reasons why a business or a bureau might have failed; cut funding, corrupt oversight, deliberate mismanagement. It is not logically valid to apply the effect to cause as opposed to the other way around.

Denying the Antecedent
If A, B; not A, so not B

A similar form of user-defined business logic fallacy to affirming the consequent, denying the antecedent is the same basic idea in reverse. It also takes the extension from cause to effect and reverses it, but this time, in the negative. Consider the following: If I went to California, I would get a tattoo. I did not go to California, so I did not get a tattoo. The logic of the original statement only implies something that would happen, not that it wouldn’t if the conditions were not met. I very well could have stayed home from California, then get the tattoo because I had intended to on the trip that had fallen through.

Denying a Conjunct
Not A and B; not B; so, A

Let’s first look at this one in a somewhat reasonable light. I can’t kick butt and chew bubble gum at the same time. I’m not chewing bubble gum, so I must be kicking butt. At the face of it, it seems somewhat reasonable. Two choices are given as mutually exclusive, one of them is eliminated as an option, so the other one is true. There’s nothing about those two things being mutually exclusive, however, that means either of them has to be true at any given time. Think about the slightly more mundane example: I can’t be at school and at work at the same time. I am not at work. Therefore, I am at school. Why would you have to be at either? The statement can be entirely true, you can’t in fact be at both of those places, but you could also be at neither of those places. You could be at home, or at the park, or sleeping.