LSAT Logical Reasoning key terms

A passage in which a speaker offers evidence and draws a conclusion from it. Logical Reasoning questions ask you to analyze, strengthen, weaken, or otherwise evaluate such passages.

A statement offered as support for a conclusion. Premises are the reasons given; they are meant to be accepted as true rather than argued for within the passage.

The claim the author wants you to accept, supported by the other statements in the passage. It is the main point the argument is trying to establish.

A conclusion drawn from evidence rather than stated outright. On the test, an inference must be supported by the passage, though it need not follow with logical certainty.

An unstated belief the author relies on to move from premises to conclusion. If the assumption is false, the argument falls apart; it is a necessary bridge.

A statement that, if added to the premises, guarantees the conclusion follows. It is enough on its own to make the argument valid, even if it is stronger than needed.

A statement the argument cannot do without; if it is false, the conclusion cannot be properly drawn. It is required, though it may not be enough to prove the conclusion.

A property of arguments in which the conclusion follows with certainty from the premises. A valid argument can still have false premises, so validity concerns structure, not truth.

A property of arguments that are both valid and have all true premises. Soundness requires good structure plus factual accuracy, making the conclusion guaranteed true.

A question type asking you to choose the answer that makes the argument more likely to be correct. The right answer supports the link between premises and conclusion.

A question type asking you to choose the answer that makes the argument less likely to be correct. The right answer undermines the reasoning, often by exposing an alternative explanation or flaw.

A defect in reasoning that prevents the conclusion from being properly supported. Flaw questions ask you to describe the error in abstract terms rather than fix it.

A flaw in which the conclusion is used, directly or in disguised form, as one of its own premises. The argument assumes what it sets out to prove.

A flaw that attacks the person making a claim rather than addressing the claim itself. Discrediting a speaker does not by itself show that the speaker's conclusion is false.

A flaw in which an opponent's position is distorted or exaggerated, then the distorted version is attacked. The argument refutes a claim the opponent never actually made.

A flaw that presents only two options when more exist, forcing a choice between them. It wrongly assumes the alternatives are exhaustive.

Reasoning that treats two possibilities as the only options. When used correctly it reflects a genuine exclusive choice; when used as a flaw it ignores additional alternatives.

A flaw that treats two things occurring together as proof that one causes the other. Co-occurrence may instead reflect a common cause, reverse causation, or coincidence.

A different cause or account that could explain the same evidence the argument cites. Its existence weakens an argument that assumes only one explanation is possible.

A flaw in which a term changes meaning between premise and conclusion, or the argument drifts to a topic outside the original claim. The reasoning no longer connects.

A flaw that uses one word in two different senses within the same argument. The apparent logical link depends on confusing those distinct meanings.

A flaw in which the group studied is not representative of the group the conclusion describes. Results from a skewed sample cannot be generalized reliably.

A conclusion that applies a finding from a sample to a broader population. Its strength depends on how representative and large the sample is.

A flaw that draws conclusions from only the cases that remain visible or successful, ignoring those that dropped out. The missing cases can reverse the apparent pattern.

The central conclusion of a passage, as opposed to supporting details or background. Main Point questions ask you to identify the author's primary claim.

A question type asking which answer is supported by the passage and cannot be false given it. The correct answer follows from the stated information alone.

A question type asking which answer the passage gives the most evidence for, without requiring certainty. The right answer is the best-supported option among the choices.

A condition whose presence guarantees a result. In conditional statements it appears after 'if' and is enough on its own to trigger the outcome.

A condition that must hold for a result to occur, though it may not be enough by itself. In conditional statements it typically follows 'only if' or 'requires'.

A statement of the form 'if A then B,' linking a sufficient condition to a necessary one. Its contrapositive is logically equivalent, but its converse is not.

The logically equivalent form of a conditional obtained by negating and reversing its parts. 'If A then B' becomes 'if not B then not A,' which is always equally true.

A flaw that reverses a conditional statement, treating 'if A then B' as though it meant 'if B then A.' The reversed form does not follow logically.

A question type asking you to find the answer whose logical structure matches the passage's structure. Content differs, but the pattern of reasoning must be the same.

A general rule or standard that governs specific cases. Principle questions ask you to apply a rule to facts or to identify a rule underlying a judgment.

A question type presenting an unexpected or seemingly contradictory result and asking for an explanation. The correct answer reconciles the surprising facts.

To explain how apparently conflicting facts can both be true. Resolve questions require an answer that reconciles the discrepancy without rejecting either fact.

A question type asking what function a particular sentence serves in the argument, such as premise, conclusion, or counterexample. You must identify its structural job.

A question type asking you to describe how the author builds the argument, such as by analogy, by eliminating alternatives, or by citing authority. The focus is on technique.

A reasoning technique that draws a conclusion about one case by comparing it to a similar case. The argument depends on the two cases being relevantly alike.