Fallacy · Slippery words and shapes
Equivocation
Also called: One word, two meanings
Shifting between two meanings of the same word partway through an argument.
What it is
Many words have more than one sense. An argument can look valid because the same word appears in each step, when it means one thing in the first step and another in the second. With the meanings pinned down, the argument falls apart.
An example
“A feather is light. What is light cannot be dark. So a feather cannot be dark.” “Light” first means not heavy, then means bright.
How to spot it
Ask what a key word means in each step, and whether it means the same thing every time.
How to answer it
“In which sense do you mean that word? It seems to change between your premises.”
When it is not a fallacy
A word can take two senses in one argument if each step says which sense it means and the conclusion follows under that sense. The trouble starts when the shift goes unmarked.
Printable sheet of all fallacies
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A plain reference you can paste into notes or an essay:
Quest2Reason. “Equivocation.” https://quest2reason.com/learn/ideas/fallacies/equivocation. Accessed 13 November 2026.