Flawed Reasoning in LSAT Logical Reasoning Questions

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.

We have put together an article that addresses a variety of the flaws that tend to appear with some frequency. This article examines 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. Commit them all to memory and you’ll find yourself well prepared to respond to nearly any argument you come across.

Source Arguments

A common mistake found in a number of Flaw in the Reasoning questions is one that should be familiar to most test takers from their daily experiences: Source Argument. Also known as an ad hominem attack (meaning “to the person”), a Source Argument commits a singular, consistent mistake by attacking the person/group making a claim (the source), as opposed to attacking the details of the claim itself. The LSAT is concerned solely with argument forms and their validity, so by failing to address the argument and instead focusing on the character or motives of the argument’s source, an author does nothing to undermine an opponent’s position.

Most test takers should already be familiar with this flawed strategy of arguing because it is an often-favored style of rebuttal for a lot of people in daily life (particularly children and, sadly, politicians). Consider an example:

“Mayor Jones’ anti-DUI campaign should not be taken seriously. After all, the mayor himself was cited for driving under the influence in college.”

Has the statement that the mayor once committed the crime he is seeking to prevent really shown that his campaign should be ignored? Of course not. The merits of the campaign are left unchallenged by an attack on the person himself, so this argument against the mayor is a poor (flawed) one.

Typically source arguments will be easy to spot on the LSAT, as they almost always take one of two identifiable forms:

  1. Focusing on the actions of the source (as in the example above).

  2. Focusing on the motives of the source.

So when you encounter a stimulus where the author is attempting to disprove someone’s position by attacking the person or group behind that position, and you are then asked to describe the author’s error, what can you expect of the correct answer choice? Well it will contain a few predictable points: (1) it will note that the author is attempting to discredit/criticize a position or claim, and (2) it will state that the author is in error for focusing on the proponent/source of that claim. Here are a few examples of source arguments as described by the test makers:

“it is directed against the proponent of a claim rather than against the claim itself”

“it draws conclusions about the merit of a position and about the content of that position from evidence about the position’s source”

“assuming that a claim is false on the grounds that the person defending it is of questionable character”

Always be on the lookout for arguments that address the nature of a claim’s source instead of the contents of the claim itself, and when asked to describe that flaw you should be able to quickly choose the answer with the characteristics given above.

Circular Reasoning

A type of mistake that LSAT authors make in Flaw in the Reasoning questions with some frequency: Circular Arguments. Occasionally referred to as “circular reasoning,” these arguments commit a singular, recognizable error where the author’s stated conclusion (belief) is supported primarily, or even exclusively, by a premise that is the same as the conclusion. In other words, the author assumes as true (gives the premise as a truth) what is intended to be proven (the conclusion). This is a somewhat tricky idea to grasp in the abstract, so let me give you a simple example of what this might look like:

“The New England Patriots are the best football team because they’re better than the other teams.”

Do you see the restatement of just one idea in both the conclusion and its premise?

Remember, when constructing an argument the author gives the premises as factual and then from those facts attempts to draw a valid, fully supported conclusion. So the conclusion must follow from the premises. But if I’m trying to prove that “the Patriots are the best,” I need to provide actual evidence for that belief, rather than simply saying it’s true in a premise as well. And that’s how circular reasoning works: the conclusion given is based on an identical premise, which the author simply believes without evidence. The “circularity” is based on the idea that when you question the conclusion the author points to the premise (the same idea), and when you question the belief in that premise the author just gives the conclusion (same idea again), and so on, around and around without any actual evidence to show the truth of either.

See if you can spot the circularity in another example:

“I must be telling the truth, since I’m not lying.”

How would you know I’m telling the truth? Well, according to me in this example, it’s because I say I’m not lying. But you would have no more reason to believe that premise (not lying) than you would to believe the conclusion (telling the truth), and vice versa.

If you spot an argument where the conclusion is synonymous with one of the premises, and no evidence has been given to show that the premise is correct/true, you’ve got a circular argument. At that point you can quickly scan the answers for one that describes the author presuming to be true the thing he/she is attempting to prove.

Here are a few examples of how the test makers describe circular reasoning:

“it assumes what it seeks to establish”
“presupposes the truth of what it sets out to prove”
“it takes for granted the very claim that it sets out to establish”

Notice in each of these the author mistakenly believes something to be true in a premise, when it is that very thing he/she is attempting to prove in the conclusion.

A final point about circular arguments: because most test takers don’t really understand what a circular argument is, answer choices like the ones above are very commonly presented as traps following stimuli with other reasoning errors. That is, you’ll see circularity described as the flaw much more often than you’ll see circularity actually appear in the stimulus. People pick this answer choice because they don’t truly know what it means, but don’t make that mistake! Only if you see the restatement idea discussed above should you choose an answer choice that suggests circular reasoning.

Exceptional Cases and Overgeneralizations

Here we discusses a type of mistake that LSAT authors—and a LOT of real-world people—make with some frequency: Exceptional Case/Overgeneralization arguments. A stimulus with this flaw typically presents a small number of instances (maybe a single case, but never more than a few) and treats those instances as though they substantiate a broad, often sweeping, conclusion.

The error in that type of argument stems from a fundamental truth of valid conclusions: they can never be more strongly worded or absolute than the evidence given in support of them. Put more simply, a conclusion is limited by its premises. So observing a single instance of some event is not enough evidence to conclude that said event “always occurs,” or even “is likely to occur” similarly in the future, any more than the individual absence of an event would be enough to justify a belief that said event “will never occur,” or “is rare.”

You can envision this idea as almost a ladder, or staircase, of increasing certainty, where the lowest rungs/steps are reserved for ideas of mere possibility (“could occur,” “may be the case,” etc), and as we climb we find ourselves reaching heights of greater restriction, and thus greater certainty in our beliefs: above possibility is likelihood (“it will probably be the case,” “this will usually occur,” “rarely will we find,” etc), and only at the very top rungs/steps do we reach our absolutes, where our evidence is so persuasive, so strong, that we feel confident in making claims with extreme language (“it is the case that,” “this will occur only when,” “we can expect a complete absence of,” etc). We were able to climb to that height of certainty only because we had sufficient support to hold us up. Occupying a height below the last rung of evidence is easy—if you can prove something is nearly guaranteed to occur, you can certainly say with confidence that it’s possible; you simply cannot continue to safely climb above it.

Let’s pause briefly here to make something very clear: this idea of recognizing the strength of language, and its limiting effects on an author’s conclusion, is one of the most crucial considerations you must make for EVERY stimulus! They must all be viewed through this particular lens, where you contemplate the scenario described by the author and the nature of the words used to describe it—literally how the language an author chooses dictates exactly what is, and what is not, reasonably supported. So that aspect of this discussion transcends our look at common flaws, and should be a primary concern regardless of the specific stimulus or question type. As an example of the broad applicability, note that one of the most common answer choice traps in Must be True questions is an answer that is simply more extreme in its language than the premises in the stimulus allow for, which is the exact same mistake as is being described here.

Of course, this is meant to be a look at a specific argumentative error, so let’s get back to the task at hand. What exactly might an Exceptional Case or Overgeneralization flaw look like on the LSAT? Consider an example:

“My friend swears the mechanic at that shop overcharged her last week and after looking at her invoice it seems she’s right. So don’t take your business there, as you’ll definitely get ripped off.”

Or one more:

“You know, for years people have been telling me that cigarettes are bad for my health. But look at my uncle Frank: he smoked two packs every day for 83 years and outlived all my other relatives by nearly two decades!”

In either case, do we have enough evidence to draw those conclusions—“take your car there and they’ll overcharge you” and “smoking isn’t bad for my/your health”—with language that absolute? No, of course not. Granted, the first conclusion seems a little more reasonable than the second, but we’ve got only a single instance in both examples…not nearly enough support for an argument that strong.

Granted, those aren’t the most elaborate examples to work through, but they do illustrate the underlying idea and that’s what is fundamental to your ability to succeed when things get trickier. And the good news is that, just as the error is hopefully easy to recognize above, so too will it be easy to see on test day.  

If you do spot an argument where the conclusion generalizes beyond the evidence provided, you’ll want to be able to quickly scan the answers for one that describes this flaw. Here are a few examples of how that description would appear on the LSAT:

“bases a general claim on a few exceptional instances”
“supports a universal claim on the basis of a single example”
“Too general a conclusion is made about a medical procedure on the basis of a single operation”

A final point about arguments of this type: this is a very specific type of mistake and follows from a very consistent construction, so unless you see a generalized (broad) conclusion following a limited number of instances, do NOT pick an answer like those above. They are very commonly presented as traps following stimuli with other reasoning errors; in fact, answer choices describing this error are more often incorrect traps than they are correct, so be wary when you inevitably encounter them.

Errors of Composition and Division

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.  This article provides an example of a type of mistake that LSAT authors make, and certainly one you have likely encountered in your day-to-day experiences: Errors of Composition and Division.

These are actually two very closely related errors that involve questionable judgments relating an entire group to parts of the group. Taken together, you can consider these flaws a violation of this basic rule: “characteristics of an entire group are not necessarily applicable to all members of the group, and individual members of a group are not necessarily representative of the group as a whole.” However, since “Composition” and “Division” represent two separate mistakes, let’s examine them individually.

1. An error of Composition occurs when an author attributes some characteristic of members within a group or entity to either the group or entity as a whole, or to each member of the group. Quite simply that which a group is composed of may not represent the group itself.

Consider an example:

“Gas prices have been rising steadily these past few years. Thus, the cost of car ownership is higher than it was previously.”

Consider whether that conclusion—the cost of owning a car has risen—is truly proven by the premise that gas prices have gone up. Of course not. There are many, many factors that contribute to the overall cost of car ownership, only one of which is the cost of gas (and with electric cars becoming more popular gas may not be a factor at all). So you cannot assume that just because you know something about a component or entity within a group that the same information will apply to the group as a whole (or to the entire entity being considered).

On the LSAT this type of error would be represented in the answer choices as:

“assuming that because something is true of each of the parts of a whole it is true of the whole itself”
“improperly infers that each and every member has a certain characteristic from the premise that many members have that characteristic”

2. An error of Division commits a similar mistake, but in the opposite direction: an author believes that some truth about an entire group must also be true about each member of the group. That is, you cannot reliably presume facts about an entire group will still apply when the group itself is divided into smaller pieces. Let’s see how this might appear:

“The United States is the wealthiest nation in the world. So every American is wealthy.”

Again, it should be clear that the conclusion is not necessarily true! While we can make the claim that America is a wealthy nation, to assume that the same is true for every American (each is wealthy) would be a mistake.

The test makers will describe this flaw as follows:

“presumes, without providing justification, that what is true of a whole must also be true of its constituent parts”

Granted, those examples are likely more simplistic than the ones you will encounter on the LSAT, but they do illustrate the underlying idea in each error and that’s what is fundamental to your ability to succeed when things get trickier. And the good news is that, just as the error is hopefully easy to recognize above, so too will it be easy to see on test day.  

A final point about arguments of this type: this is a very specific type of mistake and follows from a very consistent construction, so unless you see a presumed relationship between a group/whole to pieces of that group/whole, do NOT pick an answer like those above. While this type of answer isn’t as commonly given as a trap as some of the other types we’ve seen, it does come up incorrectly at times as the test makers try to trick you. So be wary when you inevitably encounter them.

False Dilemma

This section discusses a type of mistake that LSAT authors make, and one you have likely experienced yourself: False Dilemma. A False Dilemma argument assumes that only two possible courses of action (or two possible choices) are available, when in fact there may be others. In fact, we can actually consider the name itself as we explore the nature of this error: “False” obviously implies the inherent mistake in the reasoning given, and “Dilemma” arises from the idea of a choice between only two options. Typically this manifests itself as the author eliminating one of the possible courses of action, and thereby concluding that the other course becomes a certainty, despite the fact that more choices/options could be available.

Let’s consider an example of how a False Dilemma argument could be made:

“Because recent polling indicates that no voters in the county are strongly in favor of the proposed amendment, we can expect strong opposition to the amendment when it is voted on next month.”

Here we have evidence that no one finds the amendment to be extremely compelling, but does that necessarily mean that those same people are therefore strongly against it? Of course not, as it is entirely possible that some voters could be neutral towards the proposal, or even just mildly in favor of it.

Here’s how that particular error would likely be represented in an answer choice:

“fails to consider that some voters may be neither strong supporters nor strong opponents of the suggested amendment.”

So on test day be sure to keep an eye out for any argument that has a binary (two-option) feel to it, and consider whether other, alternative courses of action could potentially exist. If more than two possibilities do exist, then the author has presented a False Dilemma and you can quickly scan the answer choices for the one that reflects that mistake.

NOTE: Do not confuse a False Dilemma with a situation where the author legitimately establishes that only two possibilities exist! Phrases such as “Either A or B will occur, but not both,” imply a limited set of options/possibilities, and certain real-world scenarios inherently yield only two possibilities, like “you are either dead or alive,” or “you are either in the United States or you are not.” In these cases it is reasonable to conclude one thing when the other has been ruled out.

A final point about arguments of this type: this is a very specific type of mistake and follows from a very consistent construction, so unless you see an argument where only two choices are presumed to be possible despite more existing, do NOT pick an answer like the one above. While this type of answer isn’t as commonly given as a trap as some of the other types we’ve seen, it does come up incorrectly at times as the test makers try to trick you. So be wary when you inevitably encounter them.

Uncertain Use of a Term or Concept

In this article, we’re going to talk about a type of flawed reasoning that LSAT authors make, and one that seems to confound a number of students on the actual test: Uncertain Use of a Term or Concept. This particular mistake violates an argumentative principle to which authors must adhere—as an argument progresses, each term and concept discussed must be used in a consistent, coherent fashion. If an author uses some term, or discusses some concept, in different ways in making her argument, then the argument itself becomes inherently confusing and its integrity is fundamentally undermined.

Because this can be a somewhat confusing notion to grasp in the abstract, let’s look at an example of how this specific error might appear:

Board Member: “If this company is going to maximize its profits in the coming year, we need to fully exploit all of our available resources.”
Human Resources Director: “Not so fast. Our employees are one of our most valued resources, and we have a strict policy against exploiting our workers.”

Think about what’s wrong with the HR Director’s response. While it is certainly true that employees are a resource and policies exist to protect them from exploitation, is that the same use of the word “exploit” that the Board Member intends? No, of course not. The Board Member simply means “capitalize on available opportunities to maximize profits,” whereas the HR Director interprets (incorrectly) “exploit” to mean “take advantage of in a malicious or harmful way.” Hence her response fails to address the argument made by the Board Member and is flawed as a result.

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

“depending on the ambiguous use of a key term”
“equivocates with respect to a central concept”
“it confuses two different meanings of the word ‘exploit’”

So on test day be sure to keep an eye out for any argument that uses a word or idea more than once and in an inconsistent fashion. Any time an author relies on a shifting or misconstrued meaning, then the argument contains an Uncertain Use flaw and you can quickly search for an answer choice like those presented above.

A final point about this error: because most test takers don’t really understand how this particular mistake works, answer choices like the ones above are very commonly presented as traps following stimuli with other reasoning errors. That is, you’ll see “uncertain use” or “equivocation” 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, but don’t fall victim to that trap! Only if you see the specific type of error discussed above should you choose an answer choice that suggests uncertain usage.

Internal Contradiction

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.

The Flaw we discuss in this section is among the easiest to spot on the LSAT: 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 on the LSAT, 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.

Appeal to Authority

This common flaw found in Logical Reasoning questions on the LSAT is one that has some real-world applicability, as well: Appeal to Authority. This could just as easily be titled, “Appeal to Improper Authority,” as this error occurs when an argument is based on evidence provided by someone who could be considered a person of authority/expertise on a subject, or in a field, that is not necessarily related to the subject in the conclusion. In other words, just because someone is an expert regarding one particular topic, does not necessarily qualify that person to speak with authority on other topics.

Let’s take a look at an example:

“World-renowned physicist Dr. Patricia Mitchell assures me that exposure to natural sunlight, even exposure resulting in mild sunburn, is still significantly less of a cancer risk than brief exposure to the artificial light in a tanning bed. So I make sure to tell all of my friends that if they’re looking to get a tan this summer they should do it outdoors, and not at the tanning salon!”

Granted, we could probably point out a number of errors here, but perhaps the most glaring is that the author concludes that tanning outdoors is preferable to tanning in a salon based on the opinion of a physicist (mathematician specializing in physics), when there is no reason to believe a physicist would have particularly compelling or relevant insights into biological processes such as cancer development. Were the doctor a dermatologist (skin doctor), or even a medical doctor in general, perhaps the expertise of that field would be applicable and persuasive, but a doctor of physics cannot be presumed to be an authority in a field far removed from her area of achievement.

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

“the judgment of experts is applied to a matter in which their expertise is not relevant”
“the argument improperly appeals to the authority of the supervisor”
“bases a conclusion solely on the authority of the claimant, without seeking further proof”

Two final points to consider regarding Appeal to Authority errors:

  1. 1. On rare occasions a conclusion will be based on the authority of a person or group whose expertise does seem to apply to the subject at hand, however another person or group with equally relevant authority will offer contradictory evidence or claims. In this case the Appeal to Authority error still exists, but instead of appealing to an improper authority, instead the author makes the mistake of discounting one authority in favor of another, when there is no clear indication of which authority should be considered correct. Two equally authoritative sources with contradictory views simply indicate that a strong conclusion in either direction is questionable.
  2. 2. In instances where multiple authorities are sited, the test makers won’t test your ability to determine degrees of authority or relevant knowledge; for instance, in the tanning example above they wouldn’t have a dermatologist (skin doctor) argue for tanning beds and an oncologist (cancer doctor) argue for sunlight, and then force you to decide which is more reliable authority on skin cancer.

So on test day be sure to keep an eye out for any argument that draws a conclusion based on the opinions of an authoritative source or so-called “expert.” Just because someone is a reliable authority in one particular field does not necessarily mean that expertise will be relevant to other fields.

Appeal to Emotion

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. With that in mind, let’s turn our attention to a flaw that every test taker has been subjected to at some point in his or her life, and probably attempted to utilize as well: Appeal to Emotion.

Long story short, how someone feels, or how “unfair” some situation seems, or even what one believes might be moral or immoral, does not typically provide much weight for making an objective argument. In this type of error a speaker will use emotion or emotionally-charged language to attempt to persuade a reader/listener that a particular position or belief is correct, when the emotion described gives no tangible reasons (only emotional or ethically-based ones) to accept a conclusion.

Let’s take a look at an example:  

“Professor, please, PLEASE reconsider my grade on the Final! I know I only answered 7% of the questions correctly, but I didn’t really deserve an F! In the past week I sprained my ankle, my dog ran away, and my kitchen caught on fire! I think it’s only fair I get a chance to retake the test!”

Granted, the student in this example has had a rough week, and from a causal standpoint it’s not hard to imagine that those events could have impacted test performance. But is it really accurate, or valid, to say that the student “didn’t deserve an F” after only getting 7% of the questions correct? This is a classic appeal to emotion, and while we (and even the professor) might certainly sympathize with this test taker, there’s no reason to accept the conclusion that the score was undeserved.

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

“the argument appeals to emotion rather than to reason”
“attempts to persuade by making an emotional appeal”

A final point to consider regarding Appeal to Emotion errors: just because an author talks about the idea of emotion/feelings, or similarly the idea of morally right/wrong, regarding some course of action does not necessarily mean that that is the error. It’s only when the conclusion is based on the author’s feelings, or an attempt to persuade based on the feelings of someone else, that this error occurs. So don’t just automatically choose an answer about “uses emotions to persuade” or “bases a conclusion on moral concerns rather than…” because the author uses the words “moral,” “feeling,” “emotion,” “ethical,” etc. Instead, determine whether emotions/morals are the main basis for the argument, and select that type of answer only when they are.