Flaw Questions

These questions present you with a flawed argument, and you must identify exactly what the error in reasoning is.

Every argument on the LSAT consists of a conclusion and support. The argument uses the support to prove the conclusion.

A flawed argument is simply one in which the support does not necessarily prove the conclusion.

As such, in identifying the flaw of an argument, all you have to do is show why the support doesn’t lead to the conclusion. You need to point out “wait a second, here’s how that support can be true and that conclusion can be false”. That’s all.

Here’s a simple example:

It’s almost definitely going to rain today. After all, John predicted rain, and he is an architect with many years of professional experience designing buildings.

The conclusion is the first sentence (that it’s probably going to rain today), and the second sentence is brought as the supporting point (that John the experienced architect predicted rain).

So why doesn’t that support lead to that conclusion? Easy: because John is an architect, not a meteorologist, and architects don’t necessarily know how to predict the weather. The correct answer identifying the flaw might be worded: “The argument relies on testimony from a person who has not been shown to be relevant”.

Let’s look at a very similar question from June 2007:

As you read the question, you should be thinking about disconnects between the support and the conclusion – why does this support not lead to this conclusion? If here you were thinking, “why on earth should we prioritize hospital budgeting based on testimony from a bunch of computer experts?” then you were correct. Look for that in the answers, and you find it very clearly in (B). A lot of people got this question wrong because they were looking for a more complicated flaw, but it really was that simple. Just think – if someone were to make this argument to you in real life, what would be the greatest reason that would occur to you for doubting it? That’s usually the right answer.

Here’s another one from the same section:

It often helps to break the argument down into its skeleton: “SUPPORT, therefore CONCLUSION”. This will help to illuminate the disconnect between the two.

In this case, that would look like this:


As we’ve said, an argument flaw is always “just because that evidence is true, doesn’t mean that conclusion is true.” In this case, just because a report’s author has ulterior motives, doesn’t mean it’s definitely false. If you were looking for that in the answer choices, you’d find it in (A), almost verbatim.

This is flawed logic because my motives don’t necessarily prove the veracity, or lack thereof, of my statements. Just because I want what I’m saying to be true, doesn’t entirely prove that I must be lying.

Let’s look at another one from the same test:

If we break it down into “SUPPORT, therefore CONCLUSION”, it would look like this:


Well, just because the support is true doesn’t mean the conclusion is true: just because the employees are already motivated, doesn’t mean they can’t be motivated even more by the posters!

In other words, even if they’re already motivated, these posters could still motivate them further. In other words, (E).

As you can see, every correct answer choice on a flaw question is basically a paraphrasing of “just because [evidence] is true, doesn’t mean [conclusion] is true.

Let’s look at one more from the same section:

Support, therefore conclusion”:

Consumers preferred towels washed with Fabric-Soft over towels washed without it. Therefore, Fabric-Soft is better than every other fabric softener.

And now we’ll identify the flaw in terms of “Just because support, doesn’t mean conclusion”:

Just because towels washed with Fabric-Soft are proven to be better than towels washed without it, doesn’t mean towels washed with Fabric-Soft are better than towels washed with other fabric softeners.

In other words, how do I know these consumers tested Fabric-Soft against other fabric softeners? Maybe they just tested Fabric-Soft against washing a towel with no fabric softener at all? (For example, if Tylenol works better in healing my headaches than using no medication at all, that doesn’t prove that Tylenol works better than other medications in healing my headaches. It just proves Tylenol works better than using nothing at all – maybe Advil would have worked even better.)

In other words, to prove that these consumers like Fabric-Soft better than all other fabric softeners, I’d have to know that they tested Fabric-Soft and all other fabric softeners, and liked Fabric-Soft the best. All I know is that they tested Fabric-Soft – maybe they never had the opportunity to test any other fabric softeners?

In other words, (E).

(The other answers deal with topics irrelevant to the argument. Allergies, environmental harm, and cost have nothing to do with the evidence or conclusion and wouldn’t affect the argument at all. We are strictly arguing about the effectiveness of Fabric-Soft.

In summary:

    • The flaw of an argument is the disconnect between the support and the conclusion
    • Identify the support and the conclusion, and then figure out how the support could be true and yet the conclusion could still be false – this is the disconnect
  • The correct answer will always point out that “even if this support is true, this conclusion could still be false.”

For full clarity on very tough logical reasoning questions, check out my comprehensive LSAT course.

Oh, and if you haven’t already, download your Free MasterLSAT Study Guide, which will tell you exactly what you need to do to reach a 99th-percentile score on the LSAT.

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