Four terms

Formal fallacies ā†’ Syllogistic / quantification

Four terms (or quaternio terminorum) is when you use one word to mean two different things in the same argument, so the "proof" is really a word trick. A valid syllogism needs exactly three terms, each used in the same sense throughout. If one word shifts meaning, you've effectively introduced a fourth term and the argument fails. It's a form of equivocation in a syllogistic dress.

Examples

  • Banks are places that hold money. The river has banks. So the river holds money.

  • Light things are easy to carry. This paint is light in colour. So this paint is easy to carry.

  • The end of something is its goal. Death is the end of life. So death is the goal of life.

  • Only man is rational. No woman is a man. So no woman is rational.

ā† Back to Fallacies