Equivocation: the word that changed meaning
One word, two meanings, one broken argument.
Fallacy vs. flaw, on this site. Our fallacy page on equivocation teaches the general error with everyday examples. This page is the LSAT version: in Flaw questions the right answer usually says the argument "uses a term in two different senses" or "relies on an ambiguity." Practice catching the shift, not just naming it.
Start with the general version: the fallacy page. Then come back here for the test-day version.
What it is
Equivocation happens when a key word shifts meaning between the premises and the conclusion. The argument only works if the word means the same thing throughout. It does not.
Classic LSAT disguise: a word with a technical meaning and an everyday meaning, or a word that slides from one sense to another mid-argument.
An LSAT-style example
This example is original. It is not a real LSAT question.
Dr. Rivera holds a doctorate in literature. Doctors know best about health matters. So we should follow Dr. Rivera's health advice.
The flaw: "Doctor" means PhD holder in the premise and medical expert in the conclusion. The argument needs both meanings at once, which is impossible.
How to spot it on test day
- Circle the key term in the conclusion. Now find it in the premises. Does it mean the same thing both times?
- Suspect words: "law" (scientific vs. legal), "free" (no cost vs. liberty), "natural," "theory," "significant."
- If the argument feels like a word trick rather than a reasoning step, check for the shift.
The right answer vs. the trap
The right answer
Usually "equivocates on a key term" or "uses [term] in two different senses."
The trap
"The argument attacks Dr. Rivera instead of her claims." No attack happened. Do not pick ad hominem just because a person is mentioned.
Find your weak flaws
The free diagnostic scores flaw questions separately and shows whether this pattern is costing you points.