Flawed Analogy on the LSAT: When Comparisons Break Down

An argument by analogy takes this form: situation A has property X; situation A and situation B are similar in relevant ways; therefore, situation B also has property X. The strength of the argument depends entirely on whether the similarities between A and B are the right kind — whether the features that explain X in A are also present in B.

When the argument draws an analogy between two situations that differ in a way that is directly relevant to the conclusion, the analogy is flawed. The conclusion about B does not follow because the key feature of A that licenses the conclusion is missing in B.

On the LSAT, analogy arguments appear in flaw questions, weaken questions, and as the structural move in parallel-reasoning questions.

The argument asserts: "Case A and Case B are similar; X is true in A; therefore, X is true in B." The flaw is that A and B differ in some feature — call it feature Y — that is precisely what makes X true in A and not necessarily true in B.

The correct flaw answer says something like "the two situations compared differ in a way that is relevant to the conclusion" or "the analogy fails because the cases are not similar in the way the argument assumes."

Argument: "The city of Elmwood added a third lane to its downtown highway and traffic flow improved significantly. Riverside should do the same — adding a third lane to its downtown highway will also improve traffic flow."

The analogy: Elmwood did X and got result Y; Riverside is similar to Elmwood; so Riverside will also get Y.

Flawed because: Elmwood and Riverside may differ in ways that matter. Riverside may have a different street grid, different commuter patterns, or a downtown that attracts pedestrian traffic that a highway expansion would harm. Any such difference — if relevant to traffic flow outcomes — breaks the analogy.

Weakener: "Unlike Elmwood, Riverside's downtown traffic slowdowns are caused primarily by pedestrian crossings at grade level, not by insufficient lane capacity." This shows the situations differ in a directly relevant way — so the success in Elmwood does not predict success in Riverside.

Not every argument by analogy is flawed. If two situations share the exact features that explain why X is true in the first, the analogy may be strong. The LSAT does not test you on whether analogies are perfectly rigorous — it tests whether this particular analogy fails because of a specific, relevant difference.

Look for a difference between the two cases that directly relates to why the property would or would not hold. A difference in the color of the buildings is irrelevant to a traffic argument. A difference in the structure of the road network is not.

Verbloom's argument structure view highlights when an argument transfers a conclusion from one context to another, which makes the relevant similarity-or-difference question stand out.

Parallel-reasoning questions sometimes present arguments by analogy. When the original argument uses an analogy to support its conclusion, the parallel answer must use an analogous structure — including the same move from a comparison case to a new case.

If the original analogy is flawed (a parallel flaw question), the correct answer must use a comparably broken analogy — where the cases differ in a similarly relevant way.