Yet another ad hominem. I'm not sure how you determine I am a "know-it-all" since I never claimed on this forum to know anything outside the contents of my own mind.
You seem to get rather too easily upset. I'm not sure you should have any conversation with me.
Anyway, sure, and it is not to be decided by you either. This is a forum and I give my expert opinion as a competent speaker of English.
it is an empirical question the answer to which depends on whether competent speakers of the language converge on one and only one reading regardless of context. As soon as you find a significant minority assigns it a different reading in at least some contexts, you have successfully demonstrated its ambiguity.
I agree with that but you are an incompetent reader because it is rather obvious that the ambiguity doesn't come from the argument.
That's a category error. Arguments aren't ambiguous or unambiguous, they are valid or invalid.
Sentences can be ambiguous. Arguments aren't sequences of sentences, they are webs of
propositions. If a
representation of an argument contains ambiguous sentences, than that
representation is ambiguous in that it can refer to different arguments - each of which is either valid or invalid, but not both.
The sequence of sentences McGee uses in his representation is ambiguous in several ways: There's the issue of the specific and unspecific reading of the article, the issue of what "it" refers to, and the issue of whether to interpret the "will" as a certainty or a probability. In some of its interpretations, it refers to a valid argument (if the sentence "A Republican will win the election" is interpreted as a certainty, and/or the "it" in the conclusion is taken to refer to "the Republican who wins the election"), in others it doesn't.
If we replace the ambiguous sentences with unambiguous paraphrases corresponding to a reading that results in a valid argument, we have no trouble whatsoever intuitively assessing that the argument is indeed valid.
For example:
A1: If a Republican wins the election, then if the Republican who wins the election is not Reagan, the Republican who wins the election will be Anderson.
B1: A Republican will win the election.
C1: If the Republican who wins the election is not Reagan, the Republican who wins the election will be Anderson.
Here, the conclusion is valid (though it has a presupposition, namely that a Republican wins). Similarly:
A2: If a Republican wins the election, then if it isn't Reagan who wins, it will be Anderson.
B2: It is a certainty that a Republican, whoever it is, will win the election (e. g. because we've consulted a clairvoyant who is never wrong).
C2: If it isn't Reagan who wins, it will be Anderson.
...again a valid conclusion.
If you replace the ambiguous sentences with unambiguous paraphrases corresponding to different reading, it's similarly clear that the argument is invalid.
A3: If a Republican wins the election, then if it isn't Reagan who wins, it will be Anderson.
B3: It is highly probable that Reagan (who is a Republican so I will refer to him simply as that) will win the election.
C3: If it isn't Reagan who wins, it is highly probable that Anderson will.
What McGee does is providing a context that prejudices us to read the B sentence in reading B3, but tricking us into believing that we're inside a type 1 or 2 argument.
Argument 3 is invalid, but it shares a representation with a valid argument due to linguistic ambiguities. Argument 2 is valid by virtue of
modus ponens, so he's confusing us into believing that the invalidity of argument 3 is a problem for modus ponens, and he's using linguistic ambiguity to do so.