Do idioms pose an exception to normal definite and indefinite article usage?

I found this phrase in my biology textbook (emphasis added):

...in relation to Earth's history, 100,000 years or even a million years is the blink of an eye.

The part of the phrase in question is the word "the" in italics. In this context, doesn't it make more sense to use the indefinite article "a" instead of the definite article "the", since there can be more than one "blink of an eye"? Is "a blink of an eye" incorrect in this context? Are idioms like this exceptions to normal definite and indefinite article usage, even though the literal meaning of the idiom makes better sense otherwise?

Solution 1:

As has been pointed out, the overwhelming form of the idiom is the blink of an eye. So there's no issue of correctness involved. The questioner, however, had some specific questions that deserve attention, since they suggest some underlying grammatical misunderstandings. Specifically,

In this context, doesn't it make more sense to use the indefinite article "a" instead of the definite article "the", since there can be more than one "blink of an eye"?

This is not a function of the definite article in many situations. For instance,

• We dialed the wrong number,
• *We dialed a wrong number

even though there is only one right number, and millions of wrong ones, the idiom is always the wrong number. It's natural to native speakers, and always surprises us when we first notice it.

Articles, like other syntactic particles, don't really have any dependable meaning; they're just a convenient set of labels to attach to just about any set of things we might want to distinguish from one another. They have lots of syntactic functions, though: for instance, a predicate count noun has to have an article, as well as some form of be:

• This is copper. (predicate mass noun)
• He is a doctor. (predicate count noun)
• *He is doctor.
• He is the doctor.

Only the first two sentences above are predicate noun constructions. The third is ungrammatical; and the fourth is an equative construction, with the doctor referring to some previously mentioned doctor (or, alternatively, to some social role he is acting out), but not necessarily predicating Doctorhood of him.

Is "a blink of an eye" incorrect in this context?

No, it's just rare. This question's been answered.

However, one should be careful about using the term "correct" in talking about grammar, especially English grammar, which is mostly syntax, and most especially when dealing with syntactic phenomena like articles.

Most ideas about "correctness" (and those are scare quotes) come from vague generalizations, while a great deal of fact is actually known about article usage in English. There are dozens of special uses for articles -- an applied linguist once told me he'd counted more than sixty -- and they mostly don't make much sense at all.

Why, for instance, is it The University of Michigan and not *The Michigan State University? Or The Missouri River and The Nile River, but not *The Lake Superior or *The Loon Lake?

Are idioms like this exceptions to normal definite and indefinite article usage, even though the literal meaning of the idiom makes better sense otherwise?

No, not really. There is no "normal definite and indefinite article usage" in terms of "making sense", which is a semantic concept involving meaning, not a syntactic concept involving grammar. Grammar has nothing to do with making sense; grammar has to do with constructions and how they are used.

Moral: Don't confuse names with descriptions. What's called "the definite article" isn't necessarily more "definite" (and note what a slippery concept that is :-) than anything else; it's just one more syntactic marker, like the to that marks an infinitive, or the to that marks the direct object of listen, and it's no more meaningful by itself.

Solution 2:

Both idioms,

a blink of an eye.

and

the blink of an eye.

are reasonable alternatives.

To be logical, which is somewhat contrary to the spirit of an idiom, both refer to the indeterminate 'an eye'. So whether you refer to the determined 'blink' of that undetermined eye, or some indeterminate blink, it is still indeterminate (because you don't know whose eye it is.

Google nGrams shows that 'the' much more popular than 'an':

So the direct answer to your question is yes, idioms can follow whatever rules they feel like, and so can display 'exceptions' to strict grammar.

Solution 3:

What we have here is an instance of the use of the definite article used for generic reference. In the words of the ‘Longman Student Grammar of Spoken and Written English’,

Reference is generic when a noun phrase refers to the whole class, rather than just one or more instances of the class. In English all three articles (a/an, the and zero) can be used for generic reference.

Solution 4:

As Mitch's chart makes clear, "the" is much more common than "a" in this construction. But there's nothing grammatically or logically "right" or "wrong" about either form, and "a" is far from unknown.

I think the preference for "the" is simply because most people feel it's "awkward" to use two indefinite articles in the same "set phrase" - even more so in OP's example, where there's another one in a million years just before it.

But even though we seem to prefer having at least one definite article in the expression, it's pretty clear not many of us like using "the" in both positions - (the red line right at the bottom here...)