A fallacy of ambiguity occurs whenever some sort of ambiguity is introduced either in the premises or in the conclusion itself. This type of fallacy can make a false idea appear true — but only so long as the reader does not notice the ambiguity and does not look more deeply into the argument.
It is because of such fallacies that getting clear definitions of key terms is often very important. People discussing a matter while using different or even incompatible definitions will often just end up talking past each other, creating understandings, and ultimately don't accomplish very much.
Of course, some ambiguity is unavoidable in any discussion because so many words have multiple meanings. It is therefore important to keep in mind that the mere existence of some level of ambiguity is not enough to render an argument fallacious - otherwise just about all arguments would fail.
Instead, we must here focus upon ambiguity which creates important changes in the meaning of the thoughts being conveyed.
Fallacies of Ambiguity
Accent: The fallacy of accent occurs when the meaning of a word or sentence is ambiguous and dependent on where the spoken stress is placed. It's not common to find the fallacy of accent in modern English; it's much more common in ancient Greek, the language of the philosopher who first described it: Aristotle. Loosely defined, though, the fallacy of accent can still occur.
Amphiboly: The fallacy of amphiboly occurs whenever a sentence is ambiguous because the grammar allows for multiple interpretations. Usually this happens because of defects in how the sentence is structured. Amphiboly tends to be found in humor but there are serious situations and arguments where the fallacy can be found.
Equivocation: The fallacy of equivocation is the simplest and most obvious type of ambiguity fallacy. The fallacy of equivocation occurs when a term is used with two or more meanings in the same argument. For an argument to be valid, all of the key terms and concepts must be use in the same way and with the same definitions throughout.
No True Scotsman: This is actually a combination of several fallacies. It rests ultimately on shifting the meaning of terms (which is a form of equivocation) combined with begging the question.
Illicit Observation: The fallacy of illicit observation is committed by using two terms in an argument as if they were negations or opposites of each other when they really aren't. The key is to understand the difference between contrary and contradictory terms, a technical distinction which is easy to understand but mistakes are still easy to make.
Scope Fallacy: A scope fallacy is type of amphiboly fallacy, which means that it's a fallacy that relies on ambiguities derived from grammar rather than from the definitions of words. A scope fallacy can be technical and can be difficult to recognize but it's important to understand because it can introduce significant problems in an argument.
Quantifier Fallacy: The Quantifier Fallacy is a type of Scope Fallacy, in that the scope of particular quantifiers like "some" or "every" shift during the progress of an argument.
Quoting out of Context: Every quotation is a quote without some context because you can't quote absolutely everything. A quotation become a fallacy of quoting out of context when you use a selective quotation that distorts, alters, or even reverses the originally intended meaning.
Reification / Hypostatization: The fallacy of Reification is very similar to the Equivocation Fallacy, except that instead of using one word and changing its meaning through the argument, it involves taking a word with a normal usage and giving it an invalid usage.