Conditional reasoning isn’t necessary

Let’s start with a quick refresh on LSAT strategy: On Logical Reasoning, the procedural part starts with checking the prompt before reading the passage. It looks like this:

1. Check the prompt for how the right answer will relate to the argument. You know the answer will generally either describe the support and/or conclusion in the passage, or it will be support or a conclusion that fits into the passage.
2. Read the passage and tag each statement as either conclusion, support, or background. You know conclusions get support from other statements, and background doesn’t give or get support. It’s just there for context or clarity.
3. Carefully map the wording of the answer choices to the wording of the passage. You know everything stated in every right answer will align to statements made in the passage, so anything that doesn’t gets confidently eliminated.

Got it? Let’s do this!

*PrepTest 140 is available for FREE on LawHub even if you don’t have a subscription or access through another prep app.

PROMPT: How will the right answer relate to the argument?

The prompt says the argument is “flawed”, so you should be recognizing two things here: First, the right answer will be the only one that accurately describes the support and conclusion in the passage.

Second, you know something is wrong with the reasoning. So when you read and tag the passage you’d like to either smell something fishy, or just recognize a pattern that tips you off to a common LSAT flaw.

PASSAGE: Tag the conclusion/s and support

Lawyer: [SUPPORT: If-then rule]. However, [SUPPORT], so [CONCLUSION].

LSAT world tends to make a really big deal out of if-then rules, also known as sufficient and necessary conditions. Two truths: first, they only show up on a few questions in each section, sometimes only 1 or 2. So they have pretty limited impact on your score unless you’re down to the last few points to get to your target.

Second, most questions that use them can be answered confidently and correctly without deeply considering how the rules work. And that’s what I’m going to walk through on this one. Of course I’ll also make sure the reasoning is clear to everybody, but that should just be a backup plan for top performing test-takers.

So let’s add up two common LSAT patterns we’re seeing here and let it tell us exactly which answer is correct. This is a flaw question, AND the key piece of support is an if-then rule. That means it’s basically 100% that the argument’s flaw is mixing up the sufficient and necessary conditions. Arguments can do that in two different ways, but again, those details don’t necessarily matter.

Take a look at the answers. How many of them even talk about sufficient and necessary conditions?

ANSWERS: Carefully map the wording of the answers to the passage

(C) takes a condition that by itself is enough…to also be necessary…

Just one! Enough is a synonym for sufficient. The details in this answer about an action being wrong also match what the passage talks about.

Now on test day, that wants to be good enough. You get the same points whether you can explain why (C) is correct or not! Buuut of course, I will spell it out more:

The passage says if you take something you think belongs to someone else, that’s wrong. Meyers didn’t think the compost belonged to someone else. But that doesn’t mean there couldn’t be some other reason that taking the compost was wrong. If there is another reason, then it isn’t necessary to think something belongs to someone else for taking it to be wrong.

But the conclusion says that it wasn’t wrong, based only on that one reason. So the author is assuming that’s the only possible reason. In other words, they’re saying that reason IS necessary. Which is a flaw. And that, in it’s charmingly confusing way, is what (C) says. Let’s make sure we also agree the others are wrong.

(A) confuses a factual claim with a moral judgement.

The conclusion makes a moral judgement, and it’s based on a factual claim. No confusion though.

(B) …if he had good reason to believe that it was someone else’s property

This condition doesn’t come up in the passage, so be careful. It only talks about a situation in which Meyers does NOT have reason to believe…

(D) fails to consider the possibility that the compost was Meyers’ property

Not relevant, is it? We’re told explicitly he didn’t have any reason to think it was someone else’s property, which actually covers the more specific possibility that it’s his compost. So that wouldn’t impact the validity of the argument either way. And thus, not a flaw.

(E) concludes that something is certainly someone else’s property…

No it doesn’t, it concludes that something isn’t wrong.

(C) is the correct answer. The strategic way is easier, I don’t think there’s really any doubt. Be gentle with yourself while you keep practicing enough to make it feel doable.

The big takeaway: Pattern recognition is usually a better approach to if-then rules than conditional reasoning

If you’re into diagramming and forming contrapositives, there’s absolutely nothing wrong with that. But if you automatically try to diagram and form contrapositives every time you see if-then rules, you’re almost certainly wasting some time and energy. And more than likely you’re actually leaving points on the table. LSAT strategy, folks. It’s a thing.

Common patterns in this question:

• There are usually 3-5 of these “flaw” questions in every section, which makes them one of the most common questions on the LSAT. The flaws are crazy repetitive, so with practice you’ll start recognizing a lot of them. A lot of these prompts use the phrase “vulnerable to criticism” but that’s the exact same question.
• If-then rules, a/k/a sufficient and necessary conditions. They’re sometimes tricky to follow, but at least they’re easy to recognize. And so are answers describing them. Focus on training to recognize the pattern, and make time for studying sufficient and necessary conditions more deeply only when you know for sure it’s worth points you need to hit your target.

The plan will work if you do.