Lsat Logical Fallacies

Front 1

Possible/Probable vs. Actual/Certain

Back 1

In this fallacy the evidence in the passage states that a particular thing is possible,
or likely, and then concludes that that thing is in fact the case. The problem with this is
that even something that is highly probable is still not certain. For example, it is
extremely likely that getting struck by lightning will kill you, but that doesn’t mean that
getting struck by lightning will definitely kill you.

ex:
The vast majority of all lightning strikes involving people kill the victim instantly.
Mac told me that he has been struck by lightning twice. Therefore, Mac must
either be mistaken of else he is lying.

Front 2

Not Proven vs. Disproved

Back 2

In this fallacy the arguer assumes that a lack of evidence FOR a given position is
the same as evidence AGAINST that position. A lack of definitive proof of a higher
power, does not prove that there is no higher power. This fallacy has been used against
many scientists who postulated things for which there was not yet definite proof (like
germs, or Jovian satellites). One LSAT trick is to use a conclusion that many people
believe, to see if you can recognize that an argument can be flawed even if the conclusion
is widely accepted. For example, the fact that there is no definitive proof that any human
being has telekinetic powers, does not prove that no human has telekinetic powers.
Example:
In spite of years of scientific research, and decades of space probes, there is still
no proof of intelligent life on any planet other than earth. Therefore, it is safe to
say that Earth is the only planet with intelligent life.

Front 3

Partial vs. Complete Proof

Back 3

This flaw is sometimes related to the flaws of composition/division. Proving that
something is true of a part of an entity or group does not prove that it is true of the entire
entity or group. For example, proving that the overhead light in the car doesn’t work,
does not prove that the whole car isn’t working.
Example:
Mark’s Uncle Rico had planned to take a group of students to see a football game
in the big city. Unfortunately, three of the students’ parents didn’t approve of
their children going on the trip, and refused to sign the permission slip for the
outing. Without a signed permission slip no student is allowed to go to the big
city. Therefore, Rico will have to cancel the trip.

Front 4

One Option vs. the ONLY option

Back 4

Just because a given option or solution is a viable one, does not prove that it is the only
viable option or solution. Because this type of flaw inherently assumes that there are no
other options, this flaw is also very common on assumption questions as well as flaw
questions.
Example:
In recent years, the threat of terrorist attack at major sporting events has been
steadily increasing. With fairly available technology, tens of thousands of people
could be killed in a single event. Therefore, the only way to avoid the senseless
death of thousands is to employ bomb-sniffing dogs at all sporting event venues.

Front 5

False Dilemma/False Dichotomy

Back 5

These flaws are very closely related to the one above. In this case the argument
provides evidence about two opposing cases, and then assumes that these are the only
possible cases. The main issue however is that there is at least one other possibility. You
can think of this as the forgotten baby bear fallacy. In the Goldilocks story, the Papa
Bear’s porridge is too hot and the Mama Bear’s porridge is too cold. These aren’t the
only bowls on the table, and the Baby Bear’s porridge is just right, and therefore offers a
third option.
Example:
If a person is poor then they will wish they had more and be jealous. If a person is
rich, then they will be greedy and snobbish. Since both jealousy and greed are
vices, everyone will have at least one vice.

Front 6

Word Strength Problems

Back 6

Word Strength Problems
Most of the fallacies that deal with word strength deal with moving to a comparative or
superlative in the conclusion. For example, saying that Bob is a great piano player, does
not prove that Bob is the greatEST piano player.
Example:
Mary is clearly an outstanding manager. Her employees often express their
appreciation for her outstanding skill. She has also had extremely high
performance ratings from the day that she started at the company. Therefore, she
ought to receive the award for the Best Manager this year.

Front 7

Expanded Scope/ Change of Scope

Back 7

In this flaw, evidence that proves something about a particular item or group, is
then assumed to apply to a larger item or group. In many cases this is a situation will
involve a statement about one subgroup of a category of things, which is then assumed to
extend to all other subgroups of that category. For example, just because I am good at
LSAT tests, which are a sub-group of standardized tests, does not necessarily mean that I
would do well on DAT tests which are another sub-group of standardized tests. This flaw
could also be expressed as assuming that because two things have at least one
characteristic in common, they must have other characteristics in common as well.
Example:
Maquanna loves orange juice. Since oranges are a type of citrus fruit, and
grapefruits are a type of citrus fruit, Maquanna must also love grapefruit juice.
You could also lump into this category many of the flaws that plague surveybased
conclusions. Having a non-representative sample, or insufficient sample would
easily be expanded or changed scope.

Front 8

Correlation vs. Causation

Back 8

One of the more common fallacies on the LSAT is the assumption that because
two things are correlated with one another, those two things have a particular causal
relationship. Even having established that there is some sort of correlation between two
things (statistical or otherwise), it is not clear whether there is any causal link between the
two things. There really are two potential problems with assuming a particular causal
relationship. First, it is possible that the argument mistakes the cause for the effect.
Example:
It has been shown by research that nearly 95% of homeowners with homes valued
at over $500,000 have high paying jobs. So, if you wish to get a high paying job,
you should buy a home with a value over $500,000, since this clearly leads to a
high paying job.
In this example it is fairly clear that the argument might have reversed the actual
causal relationship. It seems plausible that the high paying job is what leads to the
high value home, not the other way around.
The second possible problem in this type of reasoning is that there might be no
direct causal link between the two things at all. There could be a third factor, that
causes both phenomena, or the correlation might be pure coincidence.
Example:
A recent survey of MENSA society members revealed that the overwhelming
majority of them enjoyed doing crossword puzzles. Therefore, either enjoying
crossword puzzles helps one become a member of MENSA, or being a member of
MENSA helps one enjoy crossword puzzles.
In this example, the problem is a bit more subtle. The problem is that it is
consistent with the facts stated, that there is some third thing that is causing both
of the two things in the correlation. In this case high IQ levels might account for
both the membership in MENSA, and the enjoyment of crosswords. It is also
conceivable that the correlation is based entirely on coincidence.

Front 9

Bad If-Then Statements

Back 9

There are two forms of illegal use of the if-then statements. Both fallacies create
would-be contra positives, but don’t do it properly. To lay the groundwork for
understanding these, the antecedent is the part of the if-then statement that is before the
arrow, or inside the circle. Which makes sense antecedent = thing that is before. The
consequent is the thing that goes after the arrow, or outside the circle. It is the result of
the “if” part of the statement.

Front 10

Affirming the Consequent

Back 10

This flaw assumes that the statement “If A then B”, also means “If B then A”. It
says yes to (affirms) the “then” portion of the statement (consequent), and fallaciously
assumes that the “if” portion (antecedent) will follow. A good way to see the flaw in
action is to look at the statement “If something is a dog, then it is a mammal.” This
statement is true, but if we affirm the consequent, the flaw will be obvious. The
statement, “If something is a mammal, then it must be a dog” clearly does not correspond
to reality. If the claimant happens to be a mammal it however, it leads to a rather
humorous conclusion. To say it in another way, while being a dog is GUARANTEES that
something is a mammal, being a dog is not NECESSARY for being a mammal.
Example:
Anyone who graduates as valedictorian of their high school class will be accepted
to State College. Tico got his letter of acceptance to State College this week.
Therefore, Tico must have been the valedictorian of his high school class.

Front 11

Denying the Antecedent

Back 11

This is the other bad contra positive. It fallaciously assumes that “If A then B”
also means “If not A then not B.” To illustrate this flaw we will use the same base
sentence that we used before. “If something is a dog, then it is a mammal.” This however
does not in any way imply that “If something is not a dog it is not a mammal.” Each
person who reads this statement is evidence that the latter statement is false. Another way
of saying this is that just because ALL dogs are mammals, doesn’t mean that ONLY dogs
are mammals. Being a dog is SUFFICIENT to tell us that it is a mammal, but it is not
REQUIRED for being a mammal.
Example:
Once a company starts to lose money, their stock falls and the board of directors
inevitably fires the CEO. Megacorp has increased profits each of the last five
quarters. Therefore, Tahnee Fahlu, the CEO of Megacorp, can be certain that the
board will not fire her.

Front 12

Something else to recognize

Back 12

On top of recognizing these flaws when they occur, you also need to be able to
recognize the descriptions of these flaws in the answer choices. Usually, the answer
choices will say something to the effect that “the argument confuses a sufficient
condition for a necessary condition.” As a general rule if the answer choice says “blah
blah blah blah necessary blah blah blah blah sufficient blah blah blah,” then it is saying
“bad contrapositive.” Therefore, if the passage uses if-then statements improperly, this is
probably the correct answer. If there are no if-then statements in the passage, don’t even
bother thinking through what the answer choice is actually saying. Cross it out and move
on.
Percentages

Front 13

Percentages versus Actual Numbers

Back 13

This flaw is based on the common misconception that an increase/decrease in
percentage is identical to an increase/decrease in actual number. For example over the
last 5 years the percentage of male applicants to law school has dropped from 51% of the
applicant pool to 48% of the applicant pool. The flawed response to this information is to
then assume that there are fewer male applicants to law school than there were 5 years
ago. The actual number of male applicants has increased by several thousand. Over the
same time period, however, the number of female applicants has risen by more than ten
thousand. Thus the percentage of males has decreased, even though the actual number of
male applicants has increased.
Example:
Over the past six months the number of people with caller ID in the city has
increased by 4000. Therefore, the percentage of people with caller ID is greater
today than it was six months ago.
You should always be on your guard against this type of flaw anytime you get a
question that uses numeric or statistical data. This flaw can actually be used in both
directions. It is equally flawed to assume that an increase in actual numbers will
necessarily mean a increase in percentage as well.

Front 14

Composition and Division

Back 14

Both of these flaws ultimately deal with the discrepancy between what is true of
individual members of a group, and what is true of the group as a whole. Just because a
given individual has a particular characteristic, and belongs to a group, does not mean
that the group as a whole also exhibits that characteristic. This flaw is easy to see when
we look at sports teams. The fact that a particular player hit more home runs than any
other player in the league, does not prove that that players team hit more home runs than
any other team in the league.
Example:
Mildred recently won the scoring average title for the Pinsburg Bowling League.
Since she bowls for the Ivory Tower Bookstore team, they must have won the
League Champoinship as well.
On the flip side of things, the fact that a certain team hit more home runs than any
other team in the league, does not prove that the individual who leads the league
in home runs belongs to that team.
Example:
The University of Esoteria has a science department that is renowned for its
stellar astrophysics department. Since, Professor Spotted-Elk was named the
Esoteria Teacher of the Year by the science committee, he must be a member of
the astrophysics department.

Front 15

Faulty Comparisons

Back 15

Comparisons and analogies are automatically suspect from a logical standpoint. If
the two things that are being compared or analogized are not identical, then the strength
of the analogy or comparison is limited to the extent that the two elements are similar.
Thus, the only really good analogies from a logical standpoint would involve elements
that are virtually identical in which case there is no need for an analogy. There are
however certain types of comparisons that are more problematic than others.
In this type of flaw the argument reasons that because one thing has a
characteristic, then another thing also has the same characteristic. The flaw is that the two
things are not sufficiently similar to warrant the conclusion. In common speech, we call
this “comparing apples to oranges.” In many ways it is similar to the flaw that we
mentioned as expanded/changing scope. The evidence includes one thing and the
conclusion jumps to another thing.

Front 16

Common Answer Choices

Back 16

There are some answer choices that occur on a very regular basis, that are worth
talking about even though they are not frequently correct.

Front 17

Circular Reasoning

Back 17

This flaw is listed in a number of ways. “The argument presupposes what it sets
out to conclude.” “…assumes the truth of the proposition it seeks to establish.”
“…merely restates a piece of evidence.” Almost every LSAT tests ever given has this as
an answer choice at least twice.
There are very few examples of questions where this answer choice is actually correct.
Part of the problem is that it is extremely difficult to make a circular argument in the
limited space of a logical reasoning question without being blatantly obvious.
One example would be as follows.
Yolanda has stated that I am an honest person. Although some have questioned
the truth of this statement, I can vouch for Yolanda. She is completely trustworthy.
Therefore, her claim about me must in fact be an accurate assessment.
The conclusion that I am in fact an honest person relies on assuming that I am
telling the truth about Yolanda. So in the end, if it turns out that I am honest, then
we can trust Yolanda when she says that I am honest.

Front 18

Equivocation

Back 18

This fallacy essentially hinges on the ambiguity of words in the passage. At heart
it is to use the same word, but in two different senses of the word. The common phrasings
of this are…”uses equivocal language,” or “ relies on the ambiguous use of a key term,”
or any other phrasing that suggest that it is taking advantage of dual meanings of a single
word.
Example:
I have heard it said that America is the land of the free, and yet this can be no
more that lying propaganda. In my 4 years of living in New York, I never was
given anything that I didn’t have to pay for in some way or another.
This argument clearly is relying on the two different definitions of the word
“free.”

Front 19

Ad Hominem Attacks

Back 19

This fallacy is actually one of the most common in the political arena. Its name
comes from the latin meaning “against the man/person.” In this fallacy the argument
avoids addressing the opponent’s argument, and focuses instead on attacking the person
making the argument. The common answer choices for this fallacy are…”the argument
attacks the proponents of an argument rather than the argument itself,” or “the argument
impugns the motives of the person making the opposing argument.”
This fallacy often fools people because to a large extent we have come to accept
this as a valid form of argument. However, the character of the person making or
supporting a particular argument tells us nothing at all about whether or not the argument
is a good one.
Example:
Fahad was recently quoted as saying that the cities crime problem was the direct
result of a lack of educational opportunities for lower income young people.
However, Fahad is himself a rather seedy character, who has been seen in
conversation with several known criminals. Therefore, his remarks should be
disregarded.

Front 20

Contradictory Information

Back 20

A small number of arguments will give information in them that is inherently
contradictory. This type of flaw is not terribly common, in large part because of the
difficulty of making it hard to spot. Most of the passages are 3 sentences or less, and if
two of them contradict one another, it is usually not subtle.

Front 21

Fallacious Appeal to Authority/Opinion

Back 21

In this flaw the argument draws a conclusion based on what someone (or more
than one someone) says/believes. The problem with this is that in many cases that is not
sufficient to prove the truth of the conclusion. One form of this is to simply rely on the
statements of someone who is not necessarily an expert on the subject. A variant of this is
the appeal to public sentiment. In matters of fact (questions that have a factual answer)
what people think is irrelevant.
For hundreds of years everyone believed that the earth was flat. Therefore, the
earth must be (have been) flat.

Front 22

Assumption of Mental State

Back 22

There are very few situations where it is valid to simply assume the mental state
of someone else. This applies to people’s beliefs, goal, dreams, desires, intents, hopes,
thoughts, etc.

Front 23

Statistics

Back 23

It has been said that there are three types of deceptions. Little white lies, big fat
lies, and statistics. That is not to say all statistics are lies, but rather people frequently
misuse statistical information. To be used as valid evidence, statistics must follow a few
rules, and breaking those amounts to a flaw. Here are a few examples:
Biased Sample
In this flaw the statistic does in fact show that there is a link between two things,
or an increased likelihood of a particular phenomenon. The flaw is that the group used to
show that correlation was biased toward that correlation. For example,
In a recent survey conducted in The Vatican City, over 80% of the respondents
replied that their religious beliefs coincided most closely with that of the Roman
Catholic Church. Therefore, the Roman Catholic theology must be more popular
than other theologies.