Flaws in LSAT Logical Reasoning: Internal Contradiction

    LSAT Prep | LSAT Logical Reasoning

    [Read Part 1 , Part 2 , Part 3 , Part 4 , Part 5 , and Part 6 of this series here.]
    Logical Reasoning Bible
    Before we continue with Part Seven of our examination of common flaws found in LR questions on the LSAT, let’s once again take a brief moment to review why it’s so important to understand these argumentative errors. Here’s how I began the first post in this series, where we looked at Source Arguments:

    Considering the vast majority of LSAT Logical Reasoning questions will have an argument in their stimulus, and the vast majority of those arguments will contain some sort of flawed reasoning, I thought I would take a moment to address a variety of the flaws that tend to appear with some frequency. In a series of posts I’ll examine a number of common mistakes that authors on the test make, which should prove useful for both Flaw in the Reasoning questions (a type that accounts for about 15% of all LR questions), as well as other question types that require you to respond to argumentation.

    With that in mind, let’s turn our attention to another type of mistake that LSAT authors make, and one that I feel is among the easiest to spot on the test: Internal Contradiction. This particular mistake, also sometimes called a “self-contradiction,” occurs when an author’s conclusion is actually opposite the conclusion that is best supported by the given premises. In other words, an author will provide evidence that literally contradicts the very conclusion he or she then draws.

    Like many of the errors we have seen, this can be a somewhat confusing notion to grasp in the abstract, so let’s look at an example of how this specific error might appear:

    Mayor: During my previous term as mayor my staff and I spent a great deal of time focusing on our city’s economy, and unemployment reached an all-time high as a result. So clearly you should support my re-election campaign if you are among those still looking for a job.

    Attentive reading should make the mistake in the mayor’s argument immediately apparent: if unemployment during his last term reached an all-time high, then a greater percentage of citizens are without jobs, and hence it is completely illogical to conclude that the unemployed would desire his re-election for economic reasons. The evidence here is in direct opposition to the mayor’s conclusion, and thus an Internal Contradiction error has been committed.

    Here’s how this type of error would likely be represented in an answer choice:

    “the author makes irreconcilable presuppositions”

    “bases a conclusion on claims that are inconsistent with one another”

    “introduces information that actually contradicts the conclusion”

     A few final points to make about Internal Contradiction errors:

    1. This error is really a test of how closely you are reading, and how conscientious you are of the specific details provided in the stimulus. Most test takers (indeed, most people) are conditioned to intuitively attempt to make sense of the information they encounter, so this type of mistake often goes unnoticed as people subconsciously ignore or correct the conflicting ideas. The lesson? Read closely! In the example above, replace the word “high” with “low” and the argument makes sense, and many other instances of contradiction are equally as subtle or brief (one word can be the difference in a sound argument and an argument that is entirely self-contradictory).

    2. Because the idea of “self-contradiction” sounds to many people like “makes a mistake,” or “is in error,” answer choices like the ones above are very commonly presented as traps following stimuli with other, specific reasoning errors. That is, you’ll see “information contradicts the conclusion” described as the flaw much more often than you’ll see this type of mistake actually appear in the stimulus. People pick this answer choice because they don’t truly know what it means, or assume it simply suggests that the author’s argument is not entirely valid, but don’t fall victim to that trap! Only if you see the specific type of error discussed above—the evidence given would make an opposite conclusion seem likely—should you choose an answer choice that suggests an internal contradiction.

    So on test day be sure to keep an eye out for any argument that’s conclusion depends on conflicting or contradicting information. Only then do you have an Internal Contradiction flaw and you can quickly search for an answer choice like those presented above.


    Be sure to review the other posts addressing a wide variety of common flaws you are likely to encounter on test day. Commit them all to memory and you’ll find yourself well prepared to respond to nearly any argument you come across.