The fallacies in this section are all cases where a word or phrase is used unclearly. There are two ways in which this can occur.
(i) The word or phrase may be ambiguous, in which case it has more than one distinct meaning.
(ii) The word or phrase may be vague, in which case it has no distinct meaning.
The following are fallacies of ambiguity:
1. Equivocation
-------------------------------------------------------------------------------- Definition: The same word is used with two different meanings.
Examples: (i) Criminal actions are illegal, and all murder trials are criminal actions, thus all murder trials are illegal. (Here the term "criminal actions" is used with two different meanings. Example borrowed from Copi.) (ii) The sign said "fine for parking here", and since it was fine, I parked there. (iii) All child-murderers are inhuman, thus, no child- murderer is human. (From Barker, p. 164; this is called "illicit obversion") (iv) A plane is a carpenter's tool, and the Boeing 737 is a plane, hence the Boeing 737 is a carpenter's tool. (Example borrowed from Davis, p. 58)
Proof: Identify the word which is used twice, then show that a definition which is appropriate for one use of the word would not be appropriate for the second use
An amphiboly occurs when the construction of a sentence allows it to have two different meanings.
Examples: (i) Last night I shot a burglar in my pyjamas. (ii) The Oracle of Delphi told Croseus that if he pursued the war he would destroy a mighty kingdom. (What the Oracle did not mention was that the kingdom he destroyed would be his own. Adapted from Heroditus, The Histories.) (iii) Save soap and waste paper. (From Copi, p. 115)
Proof: Identify the ambiguous phrase and show the two possible interpretations.
Emphasis is used to suggest a meaning different from the actual content of the proposition.
Examples: (i) It would be illegal to give away Free Beer! (ii) The first mate, seeking revenge on the captain, wrote in his journal, "The Captain was sober today." (He suggests, by his emphasis, that the Captain is usually drunk. From Copi, p. 117)