Equivocation is a logical fallacy that involves taking a word with more than one definition and freely substituting one definition for another.
- "A feather is light. Therefore, a feather cannot be dark."
- There are two meanings of the word light. The first sentence assumes a meaning that is the opposite of heavy, not the opposite of dark.
This fallacy is used frequently in the service of apologetics arguments. A few relevant examples:
- Atheism is based on faith.
- There are multiple meanings of the word faith, for example things you trust in without critical analysis or things which people believe with good evidence.
- Prayer is meditation.
- Redefining prayer as only a form of mental meditation rather than petitions for things is often used to justify the efficacy of prayer in the petition context.
- "No true Scotsman" fallacy.
- When someone says, "That person wasn't really a Christian because he did that," they are relying on ambiguity in the word Christian and redefining it to suit their needs.
- The existence of laws implies a law-giver.
- Evolution is only a theory.
- This plays on the confusion between the scientific and colloquial definitions of the word theory.