These are the fallacies of _double meaning_. It is known that an equivocal term is one which permits two or more interpretations; similarly a _proposition_ which admits of two or more interpretations may be denominated equivocal. Thus the term equivocation has come to stand for all errors in language resulting from a possibility of more than one interpretation. This justifies the position of referring to all of the six fallacies in language as fallacies also of equivocation. (1) _Ambiguous middle._ Ambiguous middle explains itself. _It is the fallacy of giving to the middle term a double meaning._ In form the argument may contain but three terms, yet in meaning there are in reality four terms. For this reason ambiguous middle and the fallacy of four terms appear to be about one and the same thing; but in this treatment we shall regard them as mutually exclusive, and this is the distinction: Invalid arguments of “ambiguous middle” have only _three_ terms in form but _four_ terms in meaning. This signifies that the middle term though identical in _form_ is given a _double meaning_. Invalid arguments of “four terms” always have four terms in both _form_ and _meaning_; they are “logical quadrupeds” in every sense of the word. ILLUSTRATIONS. _Ambiguous middle._ (a) “_Necessity_ is the mother of invention,” Bread is a _necessity_, ∴ Bread is the mother of invention. (b) “_Nothing is_ better than wisdom,” Dry bread is better than _nothing_, ∴ Dry bread is better than wisdom. (c) A _church_ is a force for good in any community, A slate roof is good for a _church_, ∴ A slate roof is a force for good in any community. _Fallacies of four terms._ (a) All _true teachers_ are just, John Doe is an _educator_, ∴ John Doe is just. (b) _Milk_ is nourishing, This substance is a _white fluid_, ∴ This substance is nourishing. (c) _Thieves_ should be imprisoned, This man _has taken what does not belong to him_, ∴ This man should be imprisoned. In the “four-term” fallacies, observe that the four terms occur in the _premises_. When a fourth term is introduced in the conclusion, the material fallacy of _non sequitur_ has been committed. (2) _Amphibology_ (_or amphiboly_). Amphibology is a fallacy resulting from an ambiguous proposition rather than from the ambiguity of any particular term. _The fallacy of amphibology is committed when the spoken or written proposition conveys more than one meaning._ The ancient oracles indulged in this sort of fallacy, the reason for such indulgence being obvious; the oracles were not too positive as to the outcome of their prognostications, and therefore were especially careful to cover _every emergency_. A careless use of relative clauses and prepositional phrases often results in the fallacy of amphibology. ILLUSTRATIONS OF THE FALLACY OF AMPHIBOLOGY. (a) “You the enemy will slay.” (b) “The Duke yet lives that Henry shall depose.”