BP Flaws

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Lesson 6 Flaws, LR Questions


1. An Argument will fail to establish that the list of options is exhaustive (that no other options is available) or an argument will fail to sufficiently eliminate some of the options.
2.An argument will falsely assume that two options are exclusive (that is cannot be some combination of both)


1. the group muse be an accurate representation of the group it purports to represent
2. those surveyed must understand the survey and not have any motive to misrepresent themselves
3. any conclusions made from the survey must be intelligibly related to the questions asked in the survey


1. From the fact that a whole has a certain property, it is concluded that all/most/some of its parts must have it as well.
2. From the fact that one/most/all of the parts have a certain property, it is concluded that the whole must have this property.

Sufficiency and Necessity

1. The Fallacy of the Converse

A --> B
--------- (NO)
∴ B --> A

A --> B
--------- (NO)
∴ A

2. The Fallacy of the Inverse

A --> B
--------- (Wrong!)
∴/A -->/B

A --> B
------- (Wrong!)


Correlation dose not imply causation, The fact that A always implies B, or that A always imply each other, is insufficient to conclude that A must cause B.

1. Another element could be the cause.

When the argument concludes that one phenomenon must be caused by another, the fist thing that you should identify are any plausible alternate causes. Theses can present in two different forms: 1. another element may be responsible for the effect in question, or 2. another element may be responsible for both the purported cause and the effect.

2. Reversing cause and effect

When two things are correlated, a common mistake is to assumes that one must be the cause when the other could be. When evaluating a cause conclusion, one should always check to see if the cause and its effect can be reversed.


1. Shift in Meaning

if the meaning of any key words shift in meaning during the course of an argument, the resultant argument may be invalid.

2. Related, but Distinct, Concepts

Arguments on the LSAT can also equivocate between two related, yet distinct, concepts. It is a fallacy to treat these concepts as though they are the same.



It is a fallacy to make an analogy between two items that differ in crucial respects.


it is fallacious to make inappropriate or incomplete comparisons between two things.


Ad Hominem

1. Attacking a person's character

2. Inconsistent behavior

Absence of Evidence

1. Failure to prove that a claim is false is taken as evidence that the claim is true

2. Failure to prove that a claim is true is taken as evidence that the claim is false.
can't prove true
-------------- } Big NO-NO!!!

3. Defeating the evidence for a claim is taken to show that the claim is false

Circular Reasoning

This fallacy restates the premise in an arguments conclusion rather than giving a reason for holding that premise.

(Example: I like to eat out because I enjoy different foods and restaurants.)

Percentage vs. Amount

1. Percentages cannot justify conclusions regarding definite amounts.
% vs. #
2. Definite amounts cannot justify conclusions regarding percentages.


The attempt to draw definitive conclusions about one time period(past, present, or future) from premises about another time period(past, present, or future) results in a temporal fallacy.

1.(it was) 2.(it was) 3.(it is) 4.(it is)
------ ----- ------- -------
1.(∴ it is) 2.(∴ it will be) 3.(∴ it was) 4.(∴ it will be)


Perception vs Reality

1. Inappropriate Authority
It is a fallacy to rely on an authority when the topic in question is outside their area of expertise.

2. Irrelevant Opinions
It is a fallacy to rely on the opinions of people when their opinions are irrelevant to the truth of the issue at hand.

Logical Force (Modality/Quantification)

Modality (Possible vs. Definite)

Refers to the degree of necessity surrounding an event. That fact that something is possible, or even probable, dose not entail it is certain.

could happen
------------ <-BAD
∴will happen

probable to occur
--------------- <-ERROR
∴will occur

Quantification (All vs. Most vs. Some)

'Some' premises cannot justify 'most' or 'all' conclusions. 'Most' premises cannot justify 'all' conclusions.

some some most
----- ----- ----- <-WRONG
∴most ∴all ∴all

Sebaceous Cysts


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