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Four Terms

The fallacy is committed when a standard form categorical syllogism contains four terms.

  1. "All dogs are animals, and all cats are mammals, so all dogs are mammals." The four terms are: dogs, animals, cats and mammals. Note: In many cases, the fallacy of four terms is a special case of equivocation. While the same word is used, the word has different meanings, and hence the word is treated as two different terms. Consider the following example:
  2. "Only man is born free, and no women are men, therefore, no women are born free." The four terms are: man (in the sense of 'humanity'), man (in the sense of 'male'), women and born free.
Identify the four terms and where necessary state the meaning of each term.

About Stephen Downes

Many kudos are owed to Stephen Downes, the logician who originally authored this list of fallacies and made it freely available on the Web. His basic structure remains. A mirror of Downes' original site can be found here.