Use of a term in multiple different meanings. Equivocations are a possible source of fallacies of ambiguity, as well as misunderstandings and a rhetorical device of confusion.
See, for example, the following example:
Gandalf: Have you been eavesdropping?
Sam: I haven’t dropped no eaves, Sir, honestly!
In this movie quote, Sam is trying to using the term “eavesdropping” (or “dropping eaves”) with a very different meaning than Gandalf. Indeed, it appears as if he is deliberately confusing the meaning in order to talk himself out of an unpleasant situation.
An example of an equivocation in logical statements could be the following:
Nothing light can ever be dark.
All feathers are light.
Therefore, no feather can ever be dark.
The term “light” is used in two different meanings here: in the major (first) premise is stands for the opposite of “dark”, but for the opposite of “heavy” in the minor (second) one. By equivocation of the term, this syllogism specifically commits the fallacy of the ambiguous middle term.
Equivocation of abstract terms
While such ambiguities are usually easily identified as synonyms when they refer to actually existing things or perceivable properties, this distiction can be rather difficult for abstract terms
use of synonyms for terms that stand for real life objects is usually quite easy to understand, the distinction for abstract concepts can sometimes be quite difficult, as the following example (loosely based on Thomas Aquinas) shows:
Humans are a species.
Socrates is a human.
Socrates is a species.
Here, the term “human” in the major (first) clause is used as a generic term, i.e. it refers to the genus “human” as a whole, while the same term in the minor (second) clause refers specifically to the individuals of that genus. One could thus rephrase the latter as: “Socrates is an individual of the human genus” (see also: semiotic fallacy).
Ambiguities in concepts and positions
Not only individual words or terms can be confounded due to ambiguities, but also complex concepts or positions can be affected by this. It is also valid that the more abstract and complicated they are, the more difficult it can be to recognise ambiguities.
A type of fallacy of both reasoning and argumentation that is based on vague or ambiguous definitions of terms is the Motte-and-Bailey fallacy: this is the name given to conflating two or more related, but clearly distinguishable positions, of which only one is argumentatively easy to defend. These are also often based on equivocations or even redefinitions of the terms used.
Copula and conjunctions
Not only the actual terms can be ambiguous, but also the often-overseen parts of the grammatical structure.
In particular, this concerns the verbs that define the relationship between subject and object – and especially in natural language phrases, which often do not meet the same requirements of precision as would be needed for formal logical expressions.
Consider the following example:
1 is a number.
2 is a number.
1 is 2.
Here the copula verb “is” is used in the two premises in the sense of “is an element of”, while in the conclusion it is used as “is equivalent to”. These are of course not the same
Sources of ambiguity
Words can be ambiguous in several ways; this is explained in more detail in the article on homonymy. Here are just a few examples of the different types of homonyms:
Furthermore, equivocations can arise from the fact that a term has been used in a figurative sense (see: metonymy).
Grammatical and phonetic ambiguities
If the ambiguity is due to the grammatical structure, this is called an amphiboly.
In many cases, amphiboles are linked to intonation or a specific melody of the phrase. In these cases, they are called prosodies.
If an ambiguity results from the way in which the terms are refered to, we speak of an intensional equivocation.
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