Return to Blog Homepage



Flaw Questions are the most common single question type on the LSAT. They also happen to be my favorite question type. I love pointing out people’s flaws, but people don’t always appreciate it. Like this one time, a guy at my house was about to say “glad,” but then changed it to “nice,” and it came out “glice.” I tried to point out the error, but somehow I was the bad guy?

On the LSAT, though, you get rewarded for nitpickingly sniffing out other people’s flaws. To do this, you want to put yourself in a maximally uncharitable mindset. You want to be as annoyingly skeptical and technical as possible and let nothing be taken for granted. That way, you’ll be able to identify the argument’s weak links.

But there’s another way to master flaw questions, and that is to learn the types of logical fallacies that appear most commonly on the LSAT. That way, whenever you see certain telltale markers, you will be able to anticipate the flaw an argument is probably committing. For example, whenever I see any language that sounds like an analogy, I’m thinking about a Comparison Flaw: are there any relevant differences between Case A and Case B, such that maybe we can’t conclude that things will work some way in Case B just because that’s how it went in Case A?

Anyway, here are my three favorite flaw categories:

1) The Ad Hominem Attack

This one is a common favorite, I think, because it’s easy to see how it’s a logical fallacy, but it’s also easy to fall under its persuasive powers. Plus it’s one of the most common flaws to hear, whether you’re on a playground or participating in a presidential primary debate. The ad hominem fallacy (translated literally: “to the man”) is when someone attacks the person making an argument rather than attacking the substance of the argument itself. Pretty much every statement out of Donald Trump’s mouth is ad hominem.

Media: Mr. Trump, Jeb! said your immigration plan is unrealistic.

Trump: Jeb! is a low-energy loser, and, let me tell you, his poll numbers, I’ll say this: his poll numbers.

Notice how he rarely bothers addressing the criticisms that are directed his way – he just attacks whoever it is who is questioning him. But of course, this is not a logically valid response. You can’t conclude that the message is wrong based on who the messenger is. Sure, the messenger might be unreliable or biased or a total weak loser who doesn’t want to make America great, etc. That all might be true, and it might give you a reason to be skeptical about the message, and to look at it closely. But does it actually indicate whether the message is valid or invalid? Let me tell you: no it doesn’t.

2) The Causal Fallacy

I remember when my father used to tuck me in at night. “Good night,” he’d say, “Sleep tight. And don’t forget that correlation does not mean causation.”
A logical error so common it has it’s own catchphrase, the causal fallacy is the assumption that just because two things happen at the same time – they’re correlated – doesn’t mean that one is causing the other. Sometimes, two events coincide randomly. Other times, they are associated because they’re both caused by a third thing. Still other times, there might be a causal relationship, but you can’t be sure which direction it goes in. In short: if you hear someone conclude that A caused B, you should be skeptical.

3) Circular Reasoning

Circular reasoning is more rare than some of the other fallacies on the LSAT, but it’s incredibly satisfying when you come across it. What’s going on here is that an argument assumes as a premise the very thing it is trying to show. Arguments like this can seem persuasive at first, because they can be hard to unpack. When you break them down, you find a dog chasing its own tail, an impossible Escher staircase ascending to itself…

Take this gem, courtesy of Stephen Colbert:

Colbert: The gut – that’s where the truth lies. Right down here in the gut. Do you know you have more nerve endings in your gut than you have in your head? You can look it up. Now, I know some of you are gonna say, “I did look it up, and that’s not true.” That’s because you looked it up in a book. Next time, look it up in your gut. I did. My gut tells me that’s how your nervous system works.

Colbert’s claim here is that the gut is where the truth lies. How do we know? It has more nerve endings than the brain. How do we know that? Colbert checked his gut. Why should we believe his gut? Because the gut is where the truth lies!

These were just a few of the many wonderful flaw categories you’ll find on the LSAT. Keep your eyes and ears out for the others – they’re all around us.