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.