In most contexts, 'half' is followed by an article or pronoun when used as a predeterminer. However, the inclusion of 'a' or 'an' in the structure "every half ..." is considered grammatically incorrect. To clarify, we would naturally say:

  • It reappears every half second.

as opposed to 'every half a second'.

Why is this the case? Why is the indefinite article not required in the noun phrase above?

The same goes for other noun of duration such as hour and minute (although we are more likely to say every 30 minutes and every 30 seconds respectively.)

If possible, please provide a link to go with your answer. Many thanks in advance.

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    I don't buy that ...is considered grammatically incorrect. It's extremely rare for the article to be included in AmE, but the usage has been gaining traction in BrE for the past century and more. My link is actually to half an hour, but in fact we're even more likely to include the article with half a second. Apr 4 '17 at 13:16
  • Thanks for providing a link to google ngram. I see that I shouldn't have dismissed the usage of the article in the phrases as grammatically incorrect. However, the fact still stands that the usage without the article is much more common. Why is that the case?
    Apr 7 '17 at 13:52
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    "Why?" isn't always a meaningful question when considering idiomatic usages like this - the mere fact that alternative versions exist at all means it's probably misleading to suggest that the reason we tend to prefer the more common one is because it's somehow more "correct". But having said that, I'll just note that every is a determiner, and we do tend to avoid using too many in one place (e.g. - It lasts a half-hour or It lasts half an hour, rather than It lasts a half an hour). Apr 7 '17 at 14:16

"Every half a second" is also correct. The difference is subtle.

Look at these:

I have half a dollar.

I have a half dollar.

If I say:

I'll be with you in half a second.

I'm saying that I'll be with you in 50% of a second. You can say "half of a second", but we usually leave out the "of", as we do in many cases with "half", and as I did in the cake example above.

Now, consider:

I'll be with you in a half second.

In this case we're using "half second" as a noun, a unit of time, using "a" before it.

If you do something "every half a second" or "every half (of) a second", you do it every 50% of a second.

If you do something "every half second", you do it per each noun. This is simpler and shorter to say, and we usually do this with units.

Below, both are correct, but the first is more common.

I rested every half mile.

I rested every half a mile.

By the way, "half second" may also be hyphenated, as "half-second". Both ways are commonly used.

  • Thanks for the comprehensive answer. To validate my understanding- both versions are correct and the only reason the article is excluded more often than not is because it's easier to roll off the tongue. But here's another question, when it comes to a more formal context, would you include the article or not?
    Apr 7 '17 at 14:01
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    In a formal context I would use "every half mile", but because it's more common, not because it's more formal.
    – Epanoui
    Apr 7 '17 at 14:09
  1. In "half second", half is an adjective.

  2. In "half of a second", half is a noun.

  3. "half a" to me appears as a colloquial contraction akin to woulda (would have), offa (off of) and gonna (going to). However, the usage of a is myriad, pinning it down is close to impossible because of the lack of entropy in the symbol. Several definitions stand out: used like any, each ("twice a day"), which would be redundant; like one ("a hundred times"), fused ("aback", "afoot" ...), like of ("time a day"). I wouldn't even dare to categorize those as specific types of words.

Every is understood variously:

  1. adjective,

  2. or determiner,

  3. or as part of indefinite pronouns (eg. in everywhere).

That informs the expectation of the following phrase. However the distinction is highly formal, but not definite, because of the fluent nature of language. I mean, adjective phrases can function as NP and there even is mention of determiner phrases.

So we have a multitude of different possible constructs, e.g. adjective + adjective + noun would be an adverbial object comparable to home in "go home", but there are too many combinations to really bother. After all it depends on the dialect.

Just one more note: "second('s) half" would be a viable construct, too, but highly unusual. The difference is more obvious, but also contrived, in German: Halbsekunde, Sekundenhaelfte. We actually say "halbe sekunde". The ablaut -e is the inflection of the stem "halb-". This sounds similar to the a, too. I suppose it simply sounds better and is easier to pronounce. In writing it's less useful, especially if you have the choice as in English.

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