LSAT Logical Reasoning (PowerScore)
Complete Table of Formal Logic Additive Inferences
-A table that lists all the major additive inferences that can be drawn by combining two relationships
Parallel Flaw Questions
-A Parallel Reasoning stimulus that contains flawed reasoning
Principle (PR)
-A broad rule that specifies what actions or judgments are correct in certain situations -These are not a separate question type but are instead an "overlay" that appears in a variety of question types and the presence of the Principle indicator serves to broaden the scope of the question
Primary Objectives
-A cohesive strategy for attacking any Logical Reasoning question -By consistently applying the objectives, you give yourself the best opportunity to succeed on each question
Fact Set
-A collection of statements without a conclusion -Fact sets make a series of assertions without making a judgment
Internal Contradiction
-A common error of reasoning (also known as a self-contradiction) that occurs when an author makes conflicting statements
Source Argument
-A common error of reasoning that attacks the person (or source) instead of the argument they advance -Because the LSAT is concerned solely with argument forms, a speaker can never validly attack the character or motives of a person; instead, a speaker must always attack the argument advanced by a person
Appeal Fallacies
-A common error of reasoning that attempts to "appeal" to various insubstantial viewpoints of the reader (emotion, popular opinion, tradition, authority, etc.) -However the appeal is not valid, and concrete evidence is needed to support the argument
False Analogy
-A common error of reasoning that involves an author using an analogy that is too dissimilar to the original situation to be applicable
Time Shift Errors
-A common error of reasoning that involves assuming that conditions will remain constant over time, and that what was the case in the past will be the case in the present or future
False Dilemma
-A common error of reasoning that involves assuming that only two courses of action are available where there may be other (for example, "you are either rich or impoverished") -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" can establish a limited set of possibilities, and certain real-world situations yield only two possibilities, such as "you are either dead or alive"
Errors of Conditional Reasoning
-A common error of reasoning that involves confusing the sufficient condition with the necessary condition -Note that the authors can either mistake a necessary condition for a sufficient condition, or mistake a sufficient condition for a necessary condition
Sufficient
-A sufficient condition can be defined as an event or circumstance whose occurrence indicates that a necessary condition must also occur
Errors of Composition and Division
-A common error of reasoning that involves judgments made about groups and parts of a group -An error of composition occurs when the author attributes a characteristic of part of the group to the group as a whole or to each member of the group -An error of division occurs when the author attributes a characteristic of the whole (or each number of the whole) to a part of the group
Exceptional Case/Overgeneralization
-A common error of reasoning that involves taking a small number of instances and treating those instances as if they support a broad, sweeping conclusion
Errors in the Use of Evidence
-A common error of reasoning that involves the misuse of evidence in one of these ways: 1. Lack of evidence for a position is taken to prove that position is false 2. Lack of evidence against a position is taken to prove that position is true 3. Some evidence against a position is taken to prove that position is false 4. Some evidence for a position is taken to prove that position is true
Numbers and Percentages Errors
-A common error of reasoning that is committed when an author improperly equates a percentage with a definite quantity, or when an author uses quantity information to make a judgment about the percentage represented by that quantity
Mistaken Cause and Effect
-A common error of reasoning that occurs because arguments that draw causal conclusions are inherently flawed because there may be another explanation for the stated relationship -This can occur by assuming a causal relationship on the basis o the sequence of events or when only a correlation exists -This can also occur due to failure to consider an alternate cause for the effect, an alternate cause for both the cause and the effect, or that the events may be reversed
Survey Errors
-A common error of reasoning that occurs when a survey uses a biased sample, the survey questions are improperly constructed or the respondents to the survey give inaccurate responses -Surveys, when conducted properly, produce reliable results -However, surveys can be invalidated when any of these errors occurs
Straw Man
-A common error of reasoning that occurs when an author attempts to attack an opponent's position by ignoring the actual statements made by the opposing speaker and instead distorts and refashions the argument, making it weaker in the process
Uncertain Use of a Term or Concept
-A common error of reasoning that occurs when the author uses a term or concept in different ways instead of using each term or concept in a constant, coherent fashion -This error is inherently confusing and undermines the integrity of the argument
Idea Umbrella
-A concept first introduced in Must Be True questions, but one which can play a role in other question types as well -Certain concepts act as an umbrella, and as such, they automatically imply other things -For example, a discussion of "all animals" thereby includes cats, zebras, lizards, etc. -In this way, elements that are not explicitly mentioned in the stimulus can still validly appear in the right answer choice
Sub-Conclusion
-A conclusion that is then used as a premise to support another conclusion -This is also known as a secondary or subsidiary conclusion
Premise
-A fact, proposition, or statement from which a conclusion is made -Literally, the premises give the reasons why the conclusion should be accepted
Circular Reasoning
-A flaw where the author assumes as true what is supposed to be proved -The premise supports the conclusion, but the conclusion equally supports the premise, creating a "circular" situation where you can move from premise to conclusion, and then back again to the premise, and so on
Test of Abstraction
-A last resort method for attacking Parallel Reasoning and Parallel Flaw questions -To use the Test of Abstraction, create a short abstract description that summarizes the "action" in the argument without referring to the details of the argument -Then compare that summary to each answer choice, eliminating the answers that are different
Most (in Formal Logic)
-A majority, and possibly all
Some Train
-A mnemonic trick used in Formal Logic where each variable is considered a "station," and the relationships between each variable are "tracks" -A successful "journey" (defined as a journey of at least two stops) yields an inference -An unsuccessful journey means no inference is present
Correlation
-A positive correlation is a relationship where the two values move together -A negative correlation is one where the two values move in opposite directions, such as with age and eyesight (the older you get, the worse your eyesight gets)
Counter-Premise
-A premise that actually contains an idea that is counter to the argument -Also called adversatives, bring up points of opposition or comparison
Argument
-A set of statements wherein one statement is claimed to follow from or be derived from the others -An argument requires a conclusion
Stimulus
-A short passage containing arguments taken from a variety of topics reflecting a broad range of academic disciplines (including letters to the editor, speeches, advertisements, newspaper articles and editorials, informal discussions and conversations, as well as articles in the humanities, the social sciences, and the natural sciences) that presents all of the necessary information to answer the subsequent question stem
Formal Logic (FL)
-A standard system of translating relationships into symbols and then making inferences from those symbolized relationships
Conclusion
-A statement or judgment that follows from one or more reasons -Conclusions, as summary statements, are supposed to be drawn from and rest on the premises
Polar Opposite
-A statement that is thee extreme opposite of another -"Hot" and "cold" are polar opposites
Argument Part Question
-A subset of Method of Reasoning questions -In Argument Part 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
Additional Premise
-Additional premises are premises that may be central to the argument or they may be secondary -To determine the importance of the premise, examine the remainder of the argument
Answer Choices
-All LSAT questions have five lettered answer choices and each question has only one correct, or "credited," response
Four Question Families
-All question types are variations of four main question "families," and each family is comprised of question types that are similar to each other
Contender
-An answer choice that appears somewhat attractive, interesting, or even confusing -Basically, any answer choice that you cannot immediately identify as incorrect
Loser:
-An answer choice which immediately strikes you as incorrect
Assumption
-An assumption is an unstated premise of the argument -Assumptions are an integral component of the argument that the author takes for granted and leaves unsaid
Sufficient Condition (S)
-An event or circumstance whose occurrence indicates that a necessary condition must also occur -The sufficient condition does not make the necessary condition occur, it is simply an indicator
Necessary Condition (N)
-An event or circumstance whose occurrence is required in order for a sufficient condition to occur
Shell Game
-An idea or concept is raised in the stimulus, and then a very similar idea appears in the answer choice, but the idea is changed just enough to be incorrect but still attractive -This trick is called the Shell Game because it abstractly resembles those street corner gambling games where a person hides a small object underneath one of three shells, and then scrambles them on a flat surface while a bettor tries to guess which shell the object is under
Complex Argument
-Arguments that contain more than one conclusion -In these instances, one of the conclusions is the main conclusion, and the other conclusions are subsidiary conclusions (also known as sub-conclusions) -In basic terms, a complex argument makes an initial conclusion based on a premise -The author then uses that conclusion as the foundation (or premise) for another conclusion, thus building a chain with several levels
Weaken Questions
-Ask you to attack or undermine the author's argument
Method of Reasoning Questions
-Ask you to describe, in abstract terms, the way in which the author made his or her argument
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
Must Be True Questions
-Ask you to identify the answer choice that is best proven by the information in the stimulus
Flaw in the Reasoning Questions
-Asks you to describe, in abstract terms, the error of reasoning committed by the author
Parallel Reasoning Questions
-Asks you to identify the answer choice that contains reasoning most similar in structure to the reasoning presented in the stimulus
Justify the Conclusion Questions
-Asks you to supply a piece of information that, when added to the premises, proves the conclusion
Causal Reasoning
-Asserts or denies that one thing causes another, or that one thing is caused by another -On the LSAT, cause and effect reasoning appears in many Logical Reasoning problems, often in the conclusion where the author mistakenly claims that one event causes another
Support/Defender Assumption Model
-Assumptions play one of two roles--the Supporter or the Defender -The Supporter role is the traditional linking role, where an assumption connects the pieces of the argument -The Defender role is entirely different, and Defender assumptions protect the argument by eliminating ideas that could weaken the argument
Some Are Not
-At least one is not, possibly all are not -Functionally equivalent to NOT ALL
Not All
-At least one is not, possibly all are not -Functionally equivalent to SOME ARE NOT
Some
-At least one, possibly all
New Element Answer
-Because correct Method of Reasoning answers must be based on elements of the stimulus, an answer that describes something that did not occur or describes an element new to the argument cannot be correct
Guessing
-Because the LSAT does not assess a scoring penalty for incorrect answer choices, you should always guess on any question that you cannot complete during the allotted time -However, because some answer choices are more likely to occur than others, you should not guess randomly
SN
-Conditional Reasoning -Abbreviation for Sufficient and Necessary Conditions -May be seen separately in diagrams as "S" and "N"
Second Family
-Consists of question types that take the answer choices as true and uses them to help the stimulus -Information outside the sphere of the stimulus is allowed in the correct answer choice -Includes the following question types: Assumption, Justify the Conclusion, Strengthen/Support, and Resolve the Paradox
Third Family
-Consists of question types that take the answer choices as true and uses them to hurt the stimulus -Information outside the sphere of the stimulus is allowed in the correct answer choice -Includes the following question type: Weaken
Supporter
-In the Supporter/Defender Assumption Model, the Supporter Assumptions link together new or rogue elements in the stimulus or fill logical gaps in the argument
Fourth Family
-Consists of question types that use the stimulus to prove that one of the answer choices cannot occur -No information outside the sphere of the stimulus is allowed in the answer choices -Includes the following question type: Cannot Be True
First Family
-Consists of question types that use the stimulus to prove that one of the answer choices must be true -No information outside the sphere of the stimulus is allowed in the correct answer choice -Includes the following question types: Must Be True/Most Strongly Supported, Main Point, Point at Issue/Point of Agreement, Method of Reasoning, Flaw in the Reasoning, and Parallel Reasoning/Parallel Flaw
Variance Test
-Consists of supplying two polar opposite responses to the question posed in the answer choice and then analyzing how the varying responses affect the conclusion in the stimulus -If different responses produce different effect son the conclusion, then the answer choice is correct -If different responses do not produce different effects, then the answer choice is incorrect -The Variance Test can only be used with Evaluate the Argument questions
Contrapositive
-Denies the necessary condition, thereby making it impossible for the sufficient condition to occur -Contrapositives can often yield important insights in Logic Games
Opposition Construct
-Efficiently summarizes the logical opposites of subjects within a limited spectrum of possibilities, such as quantity, which falls in ALL vs NOT ALL, and SOME vs NONE
Resolve the Paradox Questions
-Every Resolve the Paradox stimulus contains a discrepancy or seeming contradiction -You must find the answer choice that best explains the situation
Question Stem
-Follows the stimulus and poses a question directed in the stimulus -Make sure to read the question stem very carefully -Some stems direct you to focus on certain aspects of the stimulus and if you miss these clues you make the problem much more difficult
Either/Or
-For the purposes of the LSAT, the definition of "either/or" is "at least one of the two" -Note that this definition implicitly allows for the possibilities that both elements occur, and the existence of this possibility makes diagramming sentences containing the "either/or" term confusing -A careful examination of the definition of "either/or" reveals that a conditional relationship is at the heart of the construction: since at least one of the terms must occur, if one fails to occur then the other must occur
Exaggerated Answer
-In Must Be True and Method questions, these answers take information from the stimulus and then stretch that information to make a broader statement that is not supported by the stimulus
New Information
-In Must Be True questions, be wary of answers that present so-called new information--that is, information not mentioned explicitly in the stimulus -Although these answers can be correct when they fall under the umbrella of a statement made in the stimulus, they are often incorrect
Half Right, Half Wrong Answers
-In Must Be True, Method, and Flaw questions, the makers of the LSAT love to present answers that start out by describing something that in fact occurred in the stimulus -Unfortunately, these answers often end by describing something that did NOT occur in the stimulus
Match the Validity of the Argument
-In Parallel Reasoning questions, always make sure to eliminate any answer choice that does not match the logical force (valid or invalid) of the argument
Match the Method of Reasoning
-In Parallel Reasoning questions, if you identify an obvious form of reasoning (use of analogy, circular reasoning, conditional reasoning, etc.), move quickly to the answer choices and look for the answer with an identical form of reasoning
Match the Conclusion
-In Parallel Reasoning questions, the conclusion in the correct answer choice must match the logical force of the conclusion in the stimulus
Match the Premise
-In Parallel Reasoning questions, the premise(s) in the correct answer choice must match the logical force of the premise(s) in the stimulus
C
-In diagramming Logical Reasoning questions, "C" indicates Cause
E
-In diagramming, indicates Effect
Inference
-In logic, an inference can be defined as something that must be true -If you are asked to identify an inference of the argument, you must find an item that must be true based on the information presented in the argument
Defender
-In the Support/Defender Assumption Model, the Defender assumptions contain statements that eliminate ideas or assertions that would undermine the conclusion -In this sense, they "defend" the argument by showing that a possible source of attack has been eliminated
Double Arrow
-Indicates that the two terms must always occur together -The double arrow is typically introduced in any of the following three ways: 1. Use of the phrase "if and only if" 2. Use of the phrase "vice versa" (as in "if A attends then B attends, and vice versa") 3. By repeating and reversing the terms (as in, "If A attends then B attends, and if B attends then A attends")
Double-Not Arrow
-Indicates that two terms cannot occur together -The double-not arrow only prohibits one scenario--one where the two terms occur together
Most Supported/Most Strongly Supported Questions
-Most Strongly Supported questions are in the First Family and ask you to use the information in the stimulus to prove one of the answers as decisively as possible -Due to the weakened language in the question stem, the standard for the correct answer in these questions is less stringent
Mistaken Negation
-Negates both sufficient and necessary conditions, creating a statement that does not have to be true
Negation
-Negating a statement consists of creating the logical opposite of the statement -The logical opposite is the statement that denies the truth of the original statement, and a logical opposite is different from the polar opposite
Statement Negation
-Negating a statement means to alter the sentence so the meaning is logically opposite of what was originally stated -Negation largely consists of taking a "not" out of a sentence when one is present, or putting "not" in a sentence if one is not present
Numbers and Percentages (#%)
-Numerical situations normally hinge on three elements: an overall total, a number within that total, and a percentage within the total -LSAT problems will often give you one of the elements, but without at least two elements present, you cannot make a definitive judgement about what is occurring with another element -When you are given just percentage information, you cannot make a judgement about numbers -Likewise, when you are given just numerical information you cannot make a judgement about percentages
Reverse Answer
-Occurs when an answer choice contains familiar elements from the stimulus, but rearranges those elements to create a new, unsupported statement
Relativity Flaw
-Occurs when information about a relative relationship--one involving a comparison--is used to draw an absolute conclusion, or when a relative conclusion is drawn from absolute information -An example is: "Valentina is the tallest girl in the class, therefore Valentina is tall"
Pre-Phrasing
-One of the most effective techniques for quickly finding correct answer choices and avoiding incorrect answer choices, pre-phrasing an answer involves quickly speculating on what you expect the correct answer will be based on the information in the stimulus
Commonly Used Construction
-One of the most frequently used argument constructions raises a viewpoint at the beginning of the stimulus and then disagree with it immediately thereafter -This efficiently raises two opposing views in a very short paragraph -These stimuli are recognizable because they often begin with the phrase, "Some people claim..." or one of the many variations of this phrase
Point at Issue Questions
-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 stimuli
Point of Agreement Questions
-Point of Agreement questions ask you to identify the issue or statement that the two speakers would both agree about -Typically, these questions appear almost exclusively with two-speaker stimuli
Justify Formula
-Premises + Answer Choice = Conclusion -The Justify Formula is a useful tool for understanding how Justify the Conclusion questions work -If the answer choice is correct, the application of the Justify Formula will produce the given conclusion -If the answer choice is incorrect, the application of the Justify Formula will fail to produce the given conclusion
Opposite Answer
-Provides an answer that is completely opposite of the stated facts of the stimulus -Opposite Answers are very attractive to students who are reading too quickly or carelessly and quite frequently in Strengthen and Weaken questions
Fill in the Blank
-Questions that contain a stimulus that ends with a blank space -The question stem asks you to fill in the blank with an appropriate answer
Validity
-Reflects the logical relationship of the pieces of an argument, and how well do the premises, if accepted, prove the conclusion
Repeat Form
-Simply restates the elements of a conditional statement in the original order they appeared -This creates a valid argument
General Lack of Relevant Evidence for the Conclusion
-Some authors misuse information to such a degree that they fail to provide any information to support their conclusion or they provide information that is irrelevant to their conclusion
Mistaken Reversal
-Switches the elements in the sufficient and necessary conditions, creating a statement that does not have to be true
Conclusion Identification Method
-Take the statements under consideration for the conclusion and place them in an arrangement that forces one to be the conclusion and the other(s) to be the premise(s) -Use premise and conclusion indicators to achieve this end -Once the pieces are arranged, determine if the arrangement makes logical sense
Most Train
-The Most Train works in a very similar fashion to the Some Train, but because "most" is one step higher than SOME on the Logic Ladder, the Most Train produces stronger inferences
Conditional Reasoning
-The broad name given to logical relationships composed of sufficient and necessary conditions -Any conditional statement consists of at least one sufficient condition and at least one necessary condition -In everyday use, conditional statements are often brought up using the "if...then" constructed -Conditional reasoning can occur in any question type
Fact Test
-The correct answer to a Must Be True question (and other First Family questions) can always be proven by referring to the facts stated in the stimulus -An answer choice that cannot be substantiated by proof in the stimulus is incorrect
Effect
-The event that follows from the cause
Cause (C)
-The event that makes another occur
Diagramming
-The practice of creating symbolizations for common stimulus elements (such as a conditional relationship, or marking the stimulus in a way as to make certain parts more easily identifiable (such as the conclusion)
Scope
-The range to which the premises and conclusion encompass certain ideas -An argument with a narrow scope is definite in its statements, whereas a wide scope argument is less definite and allows for a greater range of possibility
Conclusion/Premise Indicator Form
-The test makers will sometimes arrange premise and conclusion indicators in a way that is designed to be confusing -One of their favorite forms places a conclusion indicator and premise indicator back-to-back, separated by a comma, as the following examples: -"Therefore, since..." -"Thus, because..." -"Hence, due to..."
Out of Scope Answer
-These answers simply miss the point of the argument and raise issues that are either not related to the argument or tangential to the argument
Assumption Questions
-These questions ask you to identify an assumption of the author's argument
Strengthen/Support Questions
-These questions ask you to select the answer choice that provides support for the author's argument or strengthens it in some way
Main Point (MP) Questions
-They are a variant of Must Be True questions -As you might expect, a MP question asks you to find the primary conclusion made by the author
Negative Logic Ladder
-This Ladder shows the relationship between the negative terms NONE, MOST ARE NOT, and SOME ARE NOT
Mechanistic Approach
-This approach requires you to reduce the stimulus to its component parts (a process that occurs naturally as you identify premises and conclusions), and then identify which elements appear in the conclusion but not in the premises -In a nutshell, the rules for this approach condense to: link new elements in the premises and conclusion and ignore elements common to both -The mechanistic approach works for the vast majority of Justify the Conclusion questions
Uniqueness Rule of Answer Choices
-This rule states that "every correct answer has a unique logical quality that meets the criteria in the question stem. Every incorrect answer has the opposite logical quality."
Assumption Negation Technique
-This technique requires you to logically negate the answer choice under consideration, which results in a negated answer choice that attacks the argument -If the negated answer does not attack the argument, then it is incorrect -The purpose of this technique is to take an Assumption question, which is generally difficult for most students, and turn it into a Weaken question, which is easier for most students -This technique can only be used on Assumption questions
Agree/Agree Test
-This test is used to help solve Point of Agreement questions -The correct answer choice must be one about which both speakers would say, "Yes, I agree with that statement" -If each speaker does not produce that response, the answer is incorrect
Agree/Disagree Test
-This test used to help solve Point at Issue questions -The correct answer must produce responses where one speaker would say "I agree, the statement is correct" and the other speaker would say, "I disagree, the statement is incorrect" -If those two responses are not produced, then the answer is incorrect -This test crystallizes the essence of Point at Issue questions by forcing you to concretely identify the elements that determine the correct answer
Except
-When "except" is placed in a question it negates the logical quality of the answer choice you seek -It turns the intent of the question stem upside down
Least
-When "least" appears in a question stem you should treat it exactly the same as "except" -Note: this advice holds true only when this word appears in the question stem -If you see the word "least" elsewhere on the LSAT, consider it to have its usual meaning of "in the lowest or smallest degree"
Elemental Attack
-When attacking Parallel Reasoning questions, compare the big-picture elements of the argument: intent of the conclusion, force and use of the premises, the relationship of the premises and the conclusion, and the soundness of the argument -The four tests you can use to evaluate answers are Match the Method of Reasoning, Match the Conclusion, Match the Premises, and Match the Validity of the Argument
Cause and Effect (CE)
-When one event is said to make another occur -The cause is the event that makes the other occur; the effect is the event that follows from the cause -By definition, the cause must occur before the effect, and the cause is the "activator" or "ignitor" in the relationship -The effect always happens at some point in time after the cause
Evaluate the Argument Questions
-You must decide which answer choice will allow you to determine the logical validity of the argument -Use the Variance Test to prove or disprove answers as needed
Logic Ladder
-details the relationship between ALL, MOST, and SOME
Not Necessarily True
The logical opposite of "Must Be True" -When an answer choice is not proven by the information in the stimulus
