52 terms

# LSAT - Logical Reasoning

#### Terms in this set (...)

Premise
A fact, proposition or statement from which a conclusion is made
Conclusion
A statement or judgment that follows from one or more reasons.
Conditional Reasoning
A conditional statement is, in its most easily recognized form, an "if...then..." statement. The following is, for example, a conditional statement. Conditional statements are also described in terms of sufficient and necessary conditions.
Sufficient
An event or circumstance whose occurrence indicates that a necessary condition must also occur.
Necessary
An event or circumstance whose occurrence is required in order for a sufficient condition to occur.
Explain Sufficient Necessary
If a sufficient condition occurs, you automatically know that the necessary condition also occurs. If a necessary condition occurs, then it is possible that the sufficient condition will occur, but not certain.
Example of Sufficient Necessary
Banging my shin on the table is all that is needed for me to scream in pain (i.e. it is sufficient), so banging my shin is considered the sufficient condition. I cannot bang my shin on the table without screaming in pain (screaming necessarily follows the banging of my shin), so screaming in pain is the necessary condition. You should be fine if you can simply remember that the antecedent (the phrase following the "if") is the sufficient condition for the consequent (the phrase following the "then") and the consequent is the necessary condition for the antecedent.
Contra-positive
a conditional statement derived from another by negating and interchanging antecedent and consequent
Premise Indicators
Because
Since
For
For example
For that reason that In that
Given that
As indicated by
Due to
Owing to
This can be seen from
We know this by
Conclusion Indicators
Thus
Therefore
Hence
Consequently
As a result
So
Accordingly
Clearly
Must be that
Shows that
Conclude that
Follows that
For this reason
Thirteen Logical Reasoning Types
1. Must Be True / Most Supported
2. Main Point
3. Point at issue
4. Assumption
5. Justify the conclusion
6. Strengthen / support
8. Weaken
9. Method of reasoning
10. Flaw in the reasoning
11. Parallel reasoning
12. Evaluate the argument
13. Cannot be true
Four Family Types
1. Prove
2. Help
3. Hurt
4. Disprove
Reasoning Types - Family - Prove
a. Must Be True / Most Supported
b. Main Point
c. Point at issue
d. Method of reasoning
e. Flaw in the reasoning
f. Parallel reasoning
Reasoning Types - Family - Help
a. Assumption
b. Justify the conclusion
c. Strengthen / support
Reasoning Types - Family - Hurt
a. Weaken
Reasoning Types - Family - Disprove
a. Cannot be true
Must Be True / Most Supported
This category is simply known as "must be true". Must be true questions ask you to identify the answer choice that is best proven by the information in the stimulus. Question stem examples - "if the statements above are true, which one of the following must also be true?" - which one of the following can be properly inferred from the passage?"
Main Point
Main Point questions are variant of Must Be True questions. As you might expect, a main point question asks you to find the primary conclusion made by the author. Question stem example - "the main point of the argument is that"
Point at issue
Point at issue questions require you to identify a point of contention between two speakers, and thus these questions appear almost exclusively with two-speaker stimulus. Question stem example: "larew and Mendota disagree about whether"
Assumption
These questions ask you to identify an assumption of the author's argument. Question stem example: "which one of the following is an assumption required by the argument above?"
Justify the conclusion
Justify the conclusion questions ask you to supply a piece of information that, when added to the premises, proves the conclusion. Question stem example: "which one of the following, if assumed, allows the conclusion above to be properly drawn?"
Strengthen / support
These questions ask you to select the answer choice that provides support for the author's argument or strengthens it in some way. Question stem example: "which of the following, if true, most strengthens the argument?" - "which one of the following, if true, most strongly supports the statement above?"
Every resolve the paradox stimulus contains a discrepancy or seeming contradiction. You must find the answer choice that best resolves the situation. Question stem example: "which one of the following, if true, would most effectively resolve the apparent paradox above?"
Weaken
Weaken questions ask you to attack or undermine the author's argument. Question stem example: "which one of the following, if true, most seriously weakens the argument?"
Method of reasoning
Method of reasoning questions asks you to describe, in abstract terms, the way in which the author made his or her argument. Question stem example: "which of the following describes the technique of reasoning used above?"
Flaw in the reasoning
Flaw in the reasoning questions ask you to describe, in abstract terms, the error of reasoning committed by the author. Question stem example: "the reasoning in the astronomer's argument is flawed because this argument"
Parallel reasoning
Parallel Reasoning questions ask you to identify the answer choice that contains reasoning most similar in structure to the reasoning presented in the stimulus. Question stem example: "which one of the following arguments is most similar in its pattern of reasoning to the argument above?"
Evaluate the argument
With evaluate the argument questions; you must decide which answer choice will allow you to determine the logical validity of the argument. Question stem example: "the answer to which one of the following questions would contribute most to an evaluation of the argument?"
Cannot be true
Cannot be true questions ask you to identify the answer choice that cannot be true or is most weakened based on the information in the stimulus. Question stem example: "if the statements above are true, which one of the following CANNOT be true?"
Primary Objectives
1. Determine whether the stimulus contains an argument or if it is only a set of factual statements.
2. If the stimulus contains an argument, identify the conclusion of the argument. If the stimulus contains a fact set, examine each fact.
3. If the stimulus contains an argument, determine if the argument is strong or weak.
4. Read closely and know precisely what the author said. Do not generalize!
5. Carefully read and identify the question stem. Do not assume that certain words are automatically associated with certain question types.
6. Pre-phrase; after reading the question stem, take a moment to mentally formulate your answer to the question stem.
8. Separate the answer choices into Contenders and Losers. After you complete this process, review the Contenders and decide which answer is the correct one.
9. If all five answer choices appear to be Losers, return to the stimulus and re-evaluate the argument.
Sufficient Condition Indicators
If
When
Whenever
Every
All
Any
People who
In order to
Necessary Conditions Indicators
Then
Only
Only if
Must
Required
Unless
Except
Until
Without
Must Be True Questions
Incorrect Answers In Must Be True Questions
1. Could be true or likely to be true answers
4. The shell game
Main Point Questions
Main Point Questions
Cause and Effect Reasoning
Causal Indicators
Caused by
Because of
Responsible for
Reason for
Induced by
Promoted by
Determined by
Produced by
Product of
Played a role in
Was a factor in
Is an effect of
How To Attach a Causal Conclusion - Weaken
1. Find an alternate cause for the slated effect
2. Show that even when the cause occurs, the effect does not occur
3. Show that although the effect occurs, the cause did not occur
4. Show that the stated relationship is reversed
5. Show that a statistical problem exist with the data used to make the causal statement

To Strengthen a causal argument, do the opposite of the five task above.
The Fact Test
The correct answer to a Must Be True question can always be proven by referring to the facts in the
stimulus.
Assumption
Questions ask you to identify a statement that the argument assumes or supposes. An assumption is simply an unstated premise-what must be true in order for the argument to be true. In conditional reasoning terms, an assumption can be defined as what is necessary for the argument to be true.
Justify the Conclusion
Questions ask you to strengthen the argument so powerfully that the conclusion is made logical. Compared to a Strengthen question, the answer to a Justify question must strengthen the conclusion so it is 100% proven; anything less and the answer choice is incorrect. Logically speaking, the correct answer to a Justify the Conclusion question is sufficient to prove the conclusion when added to the premises.
Strengthen / Support
Questions ask you to support the argument in any way possible. This type of answer has great range, as the additional support provided by the answer choice could be relatively minor or major. Speaking in numerical terms, any answer choice that strengthens the argument, whether by l% or by 100%, is correct.
Typical Weaken Question Scenarios
Although there are many classical logical fallacies, the most common of which we will discuss in the
Flaw in the Reasoning section, LSAT Weaken questions tend to occur with stimuli that contain one of the following features:
l. Incomplete Information. The author fails to consider all of the possibilities, or relies upon
evidence that is incomplete. This flaw can be attacked by bringing up new possibilities or
damaging information.
2. Improper Comparison. The author attempts to compare two or more items that are
essentially different.
3. Qualified Conclusion. The author qualifies or limits the conclusion in such a way as to leave
the argument open to attack. This same flaw often appears in incorrect answer choices.

While these three scenarios are not the only ways an argument can be weak, they encompass a large proportion of the errors that appear in LSAT stimuli.
Prove Family - In
a. Must Be True / Most Supported
b. Main Point
c. Point at issue
d. Method of reasoning
e. Flow in the reasoning
f. Parallel reasoning
Help - In
a. Assumption
b. Justify the conclusion
c. Strengthen / support
Hurt - In
a. Weaken
Disprove
a. Cannot be true
Method of Reasoning
Argument Part (AP) questions are a subset of Method of Reasoning questions. In Method-AP questions, the question stem cites a specific portion of the stimulus and then asks you to identify the role the cited portion plays in the structure of the argument.
Method of Reasoning questions are simply abstract Must Be True questions: instead of identifying the facts and details of the argument, you must identify the underlying logical organization of the argument. As with any Must Be True question, answer choices can be proven or disproven by directly referring to the content of the stimulus. For example, if an answer choice claims there is a contradiction in the stimulus; search the stimulus to see if a contradiction is present. If not, the answer choice is incorrect.
Flaw in the Reasoning
Flaw in the Reasoning questions are exactly the same as Method of Reasoning questions with the important exception that the question stem indicates that the reasoning in the stimulus is flawed because the question stem reveals that a flaw is present, you need not make a determination of
The stimulus; the question stem makes the determination for you. This information provides you with a tremendous advantage because you can identify the error of reasoning in the stimulus before proceeding to the answer choices. And, if you did not realize there was an error of reasoning in the stimulus, the question stem gives you the opportunity to re-evaluate the argument and find the error of reasoning.
To identify the right answer choice, carefully consider the reasoning used in the stimulus. The correct answer will identify the error in the author's reasoning and then describe that error in general. Beware of answers that describe a portion of the stimulus but fail to identify the error in the reasoning.
Common Flaws in Reasoning
1. Uncertain Use of a Term or Concept
2. Source Argument
3. Circular Reasoning
4. Mistaken Cause and Effect
5. Error of Conditional Reasoning
6. General Lack of Support for the Conclusion
8. Exceptional Case/Overgeneralization
9. Errors in the Use of Evidence
10. Errors of Composition and Division
11. Survey Errors
12. Appeal Fallacies
Parallel Reasoning Questions
Parallel Reasoning questions ask you to identify the answer choice that contains reasoning most similar in structure to the reasoning presented in the stimulus. Since this requires you to first identify the method of reasoning used by the author, and then identify the method of reasoning present in each answer choice, these questions can be quite time consuming.
In Parallel Reasoning questions, the topical matter in the stimulus and the answer choices is irrelevant and same-subject answer choices are generally used to attract the student who fails to focus on the reasoning in the stimulus. The order of presentation of the premises and conclusion in the stimulus is also irrelevant. As long as an answer choice contains the same general parts as the stimulus, they need not be in the same order. The order of presentation does not affect the logical relationship that underlies the pieces. In summary the following element s do not need to be paralleled in a Parallel Reasoning question:
o The topic of the stimulus
o The order of presentation of the premises and conclusion in the stimulus
Parallel Reasoning Elemental Attack
1. Parallel the Reasoning
2. Parallel the Conclusion
3. Parallel the premises
4. Parallel the Validity of the Argument
5. Parallel the Abstract Structure of the Argument
Parallel Flaw Questions
Since the February 1992 LSAT, whenever a Parallel Reasoning question contains flawed reasoning, it is stated in the question stem. If there is no mention of flawed reasoning in the question stem, the reasoning in the stimulus is valid (and vice versa). when a Parallel Reasoning stimulus contains flawed reasoning, we identify it as a parallel Flaw question. Like Flaw in the Reasoning questions, Parallel Flaw questions use many of the common forms of erroneous reasoning. The one important thing to remember is that rules for paralleling arguments discussed earlier apply. Equally to Parallel Flaw questions.
o Here are two Parallel Flaw question stem examples. They are virtually identical to the previous Parallel Reasoning question stems with the exception that they contain a term indicating that the reasoning in the stimulus is invalid:
"The flawed reasoning in which one of the following is most similar to the flawed reasoning in the argument above?"
"The questionable pattern of reasoning in the argument is most similar to that in which one of the following?"