I am reading Essentials of Logic, 2e by Irving M. Copi. And I do not understand this exercise from page 87.

Identify the fallacy of ambiguity that best characterizes each passage.


  1. Being perfectly frank, you should probably lie about who spilled the milk.

The solution says Amphiboly, but I found this is not obvious for me. Could you please explain why there is Amphiboly in this sentence?

  • I’m voting to close this question because this is not a homework forum – Swami Vishwananda Apr 14 at 6:32

Well, amphiboly is grammatical ambiguity where a sentence could be read multiple ways. Perhaps it's about to whom the phrase "being perfectly frank" refers - the speaker or the person to whom he's speaking. Is there any additional context for this sentence?

  • No, there is only one sentence and no additional context. But I wonder what does it mean if "being perfectly frank" is refer to the listener? Does that mean speaker asks him to "lie in a very frank way"? – Page David Apr 13 at 5:29
  • @PageDavid Yes. It's a pretty weak example of amphiboly if that's what they mean, but that's all I can think of. Really it doesn't seem like a good example, unless I've missed something. – causative Apr 13 at 5:32
  • I honestly can't interpret the "being perfectly frank" as referring to the listener without squinting very hard. – T. Sar Apr 13 at 18:06

In the book, amphiboly is defined as "when an ambiguous statement serves as a premise with the interpretation that makes it true and a conclusion is drawn from it on an interpretation that makes the premise false".

The fallacy always applies to an argument. An ambiguous statement is not amphiboly. There has to be a conclusion resulting from the ambiguous statement.

Under this definition, "being perfectly frank" is the ambiguous statement as @causative answered.

If "being perfectly frank" refers to "you", it then serves as a premise, and "you should probably lie ..." is the conclusion.

The conclusion, of course, contradicts the premise and thus drawn from an interpretation that makes the premise false (i.e. "I" am being frank, not "you").

You can compare this to the bigamy example given in the book as well.


The site Logically Fallacious defines the ambiguity fallacy as follows, and includes amphiboly in the definition:

When an unclear phrase with multiple definitions is used within the argument; therefore, does not support the conclusion. Some will say single words count for the ambiguity fallacy, which is really a specific form of a fallacy known as equivocation.

Perhaps the ambiguity is in “probably”, which does not support an absolute conclusion. Perhaps the ambiguity is in the situation where it is frankness to recommend dishonesty.

How about that? An ambiguous question about amphiboly. That’s called irony, boys and girls. Or maybe it’s a trick question?

  • Yeah, "probably" is what struck me as the offender before I took a look at any answers. – GHOST-34 Apr 13 at 15:40

For me, the ambiguity comes from "being perfectly frank". Who is perfectly frank ? If it is the person talking, then the sentence is grammatically incorrect as the subject of the second proposition should also be the person speaking, i.e. me/I, and not you. However, when we first read this part of the sentence, we may expect that the person giving the advice presents themself as frank.

If the person that is perfectly frank is then the interlocutor (you), then how can you be perfectly frank and lying about the milk at the same time ? This sentence doesn't really make sense.

The premise is hence missleading, and that's where the amphiboly comes from in my opinion.

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