Quote…

[A]n adjective placed before two juxtaposed nouns is apparently the servant of either master. So "Fabulous Christmas Bargains" is taken to mean fabulous…bargains for Christmas, whereas "Continental Holiday Brochures" are brochures for continental holidays. It is no answer to say that commonsense will guide us to the right interpretation; bargains for a wonderful Christmas and continental leaflets for holidays are both real concepts. And what of the shop's apology based on "Temporary Assistant Shortage"?―is this a shortage of temporary assistants…or a temporary shortage of assistants (whether they are permanent or not)? It will be realised that this seemingly pithy form of expression is always technically open to two meanings, is sometimes actually so, and is occasionally bizarre….

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Source: Basil Cottle, The Plight of English: Ambiguities, Cacophonies and Other Violations of Our Language (Arlington House, 1975), pp. 33-34.

Example:

All that glitters is not gold.
This rock glitters.
Therefore, this rock is not gold.

Exposition:

"Scope" is a technical notion, but if you're not familiar with it you can acquire a grasp of it through examples. For instance, consider the famous saying:

All that glitters is not gold.

This proposition is ambiguous because the scope of the negation—"not"—is ambiguous. There are two possible scopes, and thus two possible interpretations of the saying:

1. Narrow scope: The "not" negates the predicate "is gold", so that the saying is equivalent to:

   All that glitters is non-gold.

   This is the most literal interpretation of the proposition, since the negation actually occurs in the middle of the predicate: "is not gold". However, since gold does glitter, this interpretation makes the saying into a false proposition.

2. Broad scope: The "not" negates the entire rest of the sentence, that is: "all that glitters is gold". In other words, the proposition is equivalent to:

   Not all that glitters is gold.

   This, of course, is the correct interpretation, meaning that some things which glitter are non-gold, for instance, fool's gold. Or, in another cliché, don't judge a book by its cover.

Logical terms such as "not" have a scope, that is, a part of the proposition in which they occur that they affect logically. For example, "not" logically negates some part of the proposition, or the proposition taken as a whole, and this is its scope.

In the artificial languages of logic, scope ambiguity is avoided by conventions for interpreting propositions, and by introducing additional punctuation (usually parentheses) to indicate scope. Contrastingly, in natural languages, while there are various grammatical devices to indicate scope, ambiguity is still frequent. Often, natural language is disambiguated by common sense knowledge that we bring to our interpretations. For instance, in the example, we automatically reject the first interpretation because that would make the proposition false. Thus, scope ambiguity in natural language is often not obvious until pointed out, or exploited for humor.

Usually, scope ambiguity takes the form of a "broad" and "narrow" scope, as in the example, where the broad scope often is the entire sentence, and the narrow scope is some smaller part of it. Since this is a type of structural ambiguity, and not equivocation on the meaning of words, scope ambiguity is a type of amphiboly.

The following types of logical and grammatical categories have scope, and are therefore liable to ambiguities of scope in natural languages:

• Propositional connectives: "not", "and", "or", etc.
• Quantifiers: "every", "some", etc. See Quantifier-Shift Fallacy
• Modalities: "possibly", "believes", "ought", etc. See Modal Scope Fallacy

  Example: "If Sam Clemens was Mark Twain, then he must have written Huck Finn."

  This sentence has two possible meanings depending upon the scope of "must":

  1. Narrow scope: The scope of "must" is the consequent of the conditional: Given that Sam Clemens and Mark Twain were the same person, then this person had to write Huck Finn, that is, he could not do otherwise. This interpretation, of course, is false.
  2. Wide scope: The scope of "must" is the conditional proposition as a whole: It necessarily follows from the fact that Sam Clemens was identical with Mark Twain, that he wrote Huck Finn. This is the correct interpretation; since we know that Mark Twain wrote Huck Finn, it follows with necessity from the fact that Sam Clemens was Mark Twain that Clemens wrote Huck Finn.
• Adverbial and adjectival modifiers:

  Example: "little girls' school"

  This phrase has two possible meanings depending upon the scope of "little":

  1. Narrow scope: A school for small girls. "Little" modifies "girls'".
  2. Wide scope: A girls' school which is small. "Little" modifies "girls' school".

Scope ambiguities, as ambiguities in general, are linguistic boobytraps which can cause people to fall into fallacy. Of all amphibolies, scope ambiguities seem to be those most likely to cause fallacious reasoning, especially in philosophical and pseudo-philosophical arguments.

Funny Fallacy:

Monsieur Lebec: (To Chuck) I'm afraid your friend hasn't told you everything. He promised to take us to a lost diamond mine, you see. (To Fearless) What kind of diamonds are in it?

Fearless: Lost diamonds.

Source: The Road to Zanzibar (1941).

Subfallacies:

• Modal Scope Fallacy
• Quantifier-Shift Fallacy

Source:

Ted Honderich (editor),The Oxford Companion to Philosophy, 1995.