Logic 101 Part 2: Spotting and Avoiding Fallacies
In Part 1, we talked about what makes an argument good: structure, validity, and soundness. But of course, not every argument lives up to those standards. In fact, many arguments fail because they commit fallacies which are errors in reasoning that break the link between premises and conclusion.
As a debater and a thinker, being able to spot these is one of your most powerful skills. Although we will not put too much emphasis on looking into specific fallacies, it is just important that you can recognize in general what failures in reasoning would look like.
Table of Contents
What is a Fallacy?
Fallacy: A mistake or error in reasoning.
There are two types of fallacies:
Formal Fallacies – Errors in the logical structure. (our main focus)
Informal Fallacies – Errors in the content, assumptions, or way the argument is framed.
We’ll examine each in turn.
Formal Fallacies
Formal fallacies are mistakes in the structure of the argument. Even if the premises sound fine, the conclusion doesn’t actually follow. So, in other words these are mistakes when it comes to validity (See Part 1). Arguments which contain formal fallacies will always be deductively invalid. Examples include
Affirming the Consequent
This fallacy occurs in conditional statements (if…then…)
If P, then Q
Q
Therefore, P
Example:
If it’s hot, Brian will sweat (P)
Brian is sweating. (Q)
Therefore, it’s hot. (Therefore P)
(Maybe Brian is just nervous!)
Denying the Antecedent
This one does get tricky because intuitively it seems correct, but it has a lot to do with the nature of conditionals and biconditionals, which we will talk about later on. Just note down for now that conditionals and biconditionals are different. Here is an example to illustrate why:
If P, then Q
Not P
Therefore, not Q
Example:
If I study, I will pass the exam.
I didn’t study.
Therefore, I won’t pass the exam.
(It is totally possible that you could still pass the exam without studying. Maybe you already knew the material, or you cheated or something to that effect)
Fallacy of the undistributed middle
This occurs in syllogisms (three-part arguments) where the middle term is not distributed in either the major or minor premise
All A are C
All B are C
Therefore, All A are B
Example
All basketball players are tall
All trees are tall
Therefore, all basketball players are trees
(Sharing properties, does not mean you are identical to something)
Remember you want to avoid these at all costs because they automatically make the entire argument invalid.
Informal Fallacies
Informal fallacies are errors in content or strategy. These are the ones you’ll encounter all the time in debate rounds. We’ll list some out quickly:
Ad Hominem – Attacking the person as a means of attacking their argument.
“Don’t listen to them; they failed math class.”
Strawman – Misrepresenting the opponent’s argument to make it easier to attack.
“They said we should cut some military spending, so clearly they want to leave the country defenseless.”
False Dilemma – Presenting two options when more exist.
“Either we ban TikTok, or every student will fail school.”
Hasty Generalization – Jumping to a conclusion from too little evidence.
“I met two rude New Yorkers, so all New Yorkers must be rude.”
Conclusion and Next Up
Fallacies are everywhere so if you can recognize them, you’ll be ahead of the game both in and out of rounds. Don’t rely on spotting them though, not every argument will be fallacious nor does an argument being fallacious, by itself, make that argument wrong. There is still legwork you have to do.
Easy enough, right? Next up in our series, we’ll get into formal argument forms and how to test validity truth tables, syllogisms, and categorical logic. (AKA the good stuff). However, before that we’ll have the practice set for this article after this, so you can practice spotting fallacies
Stay sharp. The more you practice spotting errors, the harder it will be for bad reasoning to get past you.
Stay Brilliant,
The Forensic Funnel Team
