I was reading the meaning of the term "crescent" on internet, and I spotted a part in it that led me to confusion, the definition is the following one;

A curved shape that has two narrow pointed ends, like the moon when it is less than half of a circle.

What makes me confused is the way it writes "less than half of a circle". I think of half as in this case being a noun so that the more obvious thing to do would be putting an indefinite article before it (a), but it doesn't have it. Can anyone tell me if my observation is wrong?

  • Another phrasing could be "less than a half circle." Commented May 22 at 21:23

2 Answers 2


"Half" definitely isn't an adjective in "less than half of a circle." I would say that it is a noun (or belongs to a more specific subset of the "noun" category of speech). The Cambridge Grammar of the English Language (Huddleston, Pullum et. al) calls half a noun which can be used with the function of "predeterminer" (pages 433-434 in Chapter 5, "Nouns and noun phrases", John Payne and Rodney Huddleston).

The tricky part is that nouns in English don't always follow the same rules about when they take the indefinite article. Unlike third, we often use half without any preceding determiner. It is a noun used without a determiner, which may be puzzling, but that's just the way it is sometimes in English. You can memorize "half of" with no preceding determiner as a particular construction of the word half.

  • Yes, even if you have half a lemon, you can still make some lemonade. Commented May 22 at 22:19
  • But "half" isn't a special case. "Two-thirds of" and "90% of" don't take definite articles either. Commented May 23 at 14:01
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    @DJClayworth Both those have determiners: the numerals ‘two’ and ‘ninety’. The definite article (did you mean indefinite?) is just one of many determinatives. Half is indeed a special case compared to those two – you cannot say ‘*thirds of’ or ‘*percent of’ with no determiner. [Well, you can with thirds, theoretically. If you cut a bunch of cakes into threes, you could say, “Pieces/thirds of the cakes were passed around”… but that’s just because indefinite plural nouns don’t take determiners.] Commented May 23 at 14:19
  • @DJClayworth No, thirds and percent are the nouns, each modified by quantifying determiners. Entire noun phrases with quantifiers can function as quantifiers, yes; that doesn’t make them directly comparable to half. You can add a quantifier to half/halves just the same as you can to third(s) and percent – that would make them equivalent: one half of, one third of, one percent of. The difference is that you can use half without the quantifier, but you cannot do the same with third(s) and percent. Commented May 23 at 14:27
  • @DJClayworth: "Two thirds of" and "90% of" are plural and indefinite. Either of them, and "half", can take the definite article in special contexts. What's special about "half" is that despite being singular in form, it doesn't take the indefinite article "a".
    – herisson
    Commented May 23 at 14:29

"Half" is indeed a noun here, but it is a mass noun because it specifies a continuous unit of measure that doesn't come in discrete "bits". Mass nouns do not typically take articles.

"A half of a circle" would be a semicircle: an object. "half of a circle", on the other hand, is shorthand for "the total area that amounts to one-half the area of the circle", which is a different idea. The "less than" tips you off to this implicit reference to the continuous measurement.

  • I would say "half" can be used in a discrete context as well. Half of four is two.
    – nasch
    Commented May 23 at 19:30

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