What is the difference between "a half century" and "half a century"? Is there a specific time when each phrase should be used, or is it simply a matter of preference?

  • The phrases are equivalent. The second, "half a century," is actually a very common but ungrammatical diminutive of the phrase "half of a century." The first ("a half century") is what you would expect to see in written English. The second, in colloquial spoken English. If possible, use the first, "a half century." – JBH Sep 12 '17 at 20:24
  • @JBH Do you use 'I'll be a half hour' rather than 'I'll be half an hour'? Google Ngrams seem to show that about 80% of people prefer the latter. Grammar isn't static, and if you're going to claim that 'half an hour' and 'half a century' aren't acceptable, you need to post some supporting evidence from a credible source. // 'Half an hour' is idiomatic. – Edwin Ashworth Sep 12 '17 at 20:46
  • I have to agree with Edwin Ashworth, at least for the most part. I've seen both uses rather often, so I was simply wondering which is most acceptable. New question to add onto my previous ones: Is there any real proof that one is "more" correct than the other? – DiesDunkleGehim Sep 12 '17 at 20:55
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    @JBH << half an hour noun: a period of 30 minutes I'll be back in half an hour >> [Collins] // << half an hour: 30 minutes I waited for half an hour. [M-W]. Your turn to find an authority saying it's unacceptable. – Edwin Ashworth Sep 12 '17 at 21:40
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    Probably covered as comprehensively as is possible at "Half an hour" versus "half hour", where "a half hour" is soon introduced. – Edwin Ashworth Sep 12 '17 at 22:27