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Suppose that there is a pizza.

1/2 of the pizza means a half of the pizza.

Does English use/allow the expression 0.5 of the pizza?

Suppose that a class has 10 students.

1/2 of the class means 5 students.

Does English use/allow the expression 0.5 of the class?

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  • Did you hear the phrase "half of the class" somewhere? What exactly is it that you want to say?
    – Joachim
    Apr 2, 2023 at 10:58
  • I think there were more grammatical problems with your question than whether you use a decimal number or words to talk about fractions. Tip: If the auxiliary verb is in the present or past the verb that follows is always in the infinitive.
    – Mari-Lou A
    Apr 2, 2023 at 12:06
  • You could also reasonably say ⁴⁄₈ (if the pizza were cut into eight slices) or ³⁄₆ (if it were cut into six slices). And from the perspective of pure mathematical equivalence, you could say ³⁄₆ (or ⁵⁄₁₀ or 0.5 or ⁵⁰⁄₁₀₀ or 50%) if it were cut into eight slices, since ½ = ³⁄₆ = ⁴⁄₈ = ⁵⁄₁₀ = 0.5 = ⁵⁰⁄₁₀₀ = 50%. But applying exact mathematical equivalences to parts of a simple real-world object is asking for trouble. It's reminiscent of Shylock being awarded exactly 1 pound (that is, 1.0000000... pound) of Antonio's flesh) with the proviso that, in the event of missing the mark, "thou diest."
    – Sven Yargs
    Apr 4, 2023 at 20:07
  • I suggest thinking of the fractions as ratios rather than values; that is, when referring to groups in verbal terms, "half of" means one of two, not 0.5. Those ratios are mostly interchangeable with percentages (half of ~ 50% of) but not raw numbers. You wouldn't say "one of the class" or "zero point one of the class" but rather "the whole class" or "one tenth of the class." Apr 4, 2023 at 20:57

4 Answers 4

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This is a matter of style, and style is generally a matter of personal choice. However, some styles are more widely used than others, and departing from the norm can seem awkward.

Remember that we are discussing the English language and its usages, not mathematics.

It's overkill to use decimals when what is meant is an approximation. Do you mean precisely half of the pizza, measured to the gramme, or an amount which looks close to half of it? For the class, "0.5" certainly doesn't work for an odd number of pupils.

This is reflected in how such values are read:

We say simple fractions like this:

  • ¼ a/one quarter
  • ⅛ an/one eighth
  • 3¾ three and three quarters
  • 6⅛ six and one eighth
  • ⅖ two fifths

We write and say decimals like this:

  • 0.4 [nought]† point four
  • 0.375 [nought] point three seven five

Practical English Usage 3rd Edition; Swan, OUP 2005


† Swan didn't put the brackets here, but the initial "nought" can certainly be omitted in normal use.

When writing fractions, particularly simple fractions which can be expressed in one word and don't have to mean exactly that value, it's usual to write the word:

half the class; half a pizza

For more complicated fractions, again without absolute precision, use figures:

Half the class managed to eat 6⅛ pizzas between them.

If you actually mean to be precise, and the fraction is exactly 0.375 and not more-or-less ⅜, then using decimals provides that distinction. That could apply in writing up scientific results, for example.

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  • 2
    ... and in the US you don't say "nought", you say "zero" (or sometimes "oh").
    – GEdgar
    Apr 2, 2023 at 13:48
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    Both decimals and vulgar fractions can be used to express any level of precision; neither is inherently more precise than the other. A number such as 0.5 is not very precise: it could be the result of rounding 0.46812. (In scientific contexts, 0.5 does not mean the same as 0.50000.) A fraction such as 15/32 is more precise.
    – jsw29
    Apr 3, 2023 at 14:29
3

Does English use/allow the expression 0.5 of the pizza?

Short answer: "No." Zero point five (and other decimals) is a pure number and is not used as a quantifier.

Long answer: You could possibly use this in a trivial manner, if you were giving a maths class in which you were explaining decimals to some young students:

"So if I gave point five of the pizza to you, point two-five to John, and point one to Kylie, how much is left?"

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  • Many would not consider numbers to be quantifiers, whether whole or fractions in vulgar, decimal or percentage form. [EnglishClub] Apr 2, 2023 at 15:44
  • Ah,... the nebulous "many" - I want all their names, email addresses and phone numbers... :)
    – Greybeard
    Apr 2, 2023 at 16:55
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    I give at least one reference (beats zero). I believe tchrist has put forward a reasonable argument why numerals are best considered as distinct from quantifiers. One Collins definition disallows numbers/numerals: << quantifier: In grammar, a quantifier is a word or phrase such as ' plenty' or 'a lot' which you use to refer to a quantity of something without being precise. >> Nordquist seems to agree. Apr 2, 2023 at 18:34
  • @EdwinAshworth so Norquist agrees with me when I say Zero point five (and other decimals) is a pure number and is not used as a quantifier.
    – Greybeard
    Apr 3, 2023 at 10:45
  • The terminology doesn't matter; what matters is that English places very strict limits on partitive constructions that allow cardinal numbers, fractions, and percentages but not decimals.
    – alphabet
    Apr 3, 2023 at 14:57
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As has already been pointed out, there is no strict rule about this. One can write 0.5 or ½ or 50% or half; all of these are equally intelligible, and none of them would violate any generally accepted rule of grammar. In everyday communication, however, half will be far more likely to be used than the others. Finding in your kitchen a note from somebody you live with saying 'I have left 0.5 of the pizza in the refrigerator' would be very, very odd (unless perhaps both of you are very, very nerdy), although it wouldn't be, strictly speaking, wrong.

The preference for expressing fractions in fully written out English words applies to those that are frequently dealt with in everyday contexts, such as half, third, or quarter. It does not apply to the amounts such as 17/128 or 0.731, which would be difficult to write out that way.

The only cases in which it would be natural to write 0.5 or ½ in the midst of an English sentence, are those in which comparison with other quantities expressed nearby in the same format is called for, or in which some mathematical operations will need to be performed on the quantity. One may, and perhaps should, write 0.5 in a context in which, say, 0.3 and 1.7 also appear. Similarly, one may, and perhaps should, write ½ in a context in which, say, and ¾ also appear.

This way of handling fractions is analogous to the usual way of dealing with integers, in which small numbers (e.g. seven) are normally written out as words, while larger ones (e.g. 2,437) are not, but in which all numbers appearing close to each other are expressed in the same format (e.g. 'between 7 and 2,437').

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  • I'd rather be oddly right, than popularly wrong. What is half a pizza? It's about half a pizza. I ate about half. I don't count the atoms on either side of a pizza, let alone to find out what odd or even. Always be wary of long answers. Speaking of 137, how about cutting it 37 ways into a maximum of exactly (666 +1) pieces? Or, 17 ways into a maximum of 137 pieces? Or, 9 = 1*3^2 ways into a maximum of 37 piecies? Apr 2, 2023 at 22:31
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    I don't see why this was downvoted. I also don't immediately see where that former comment is coming from.
    – Joachim
    Apr 3, 2023 at 14:41
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    I find "There is 0.5 of a pizza in the fridge" jarring. It simply doesn't work with other numbers, either whole or fractional - one would never say "There are 3 of a pizza in the fridge" or "There is 1.2 of a pizza in the fridge". At best, this could be written as "There are 0.5 pizzas in the fridge". Apr 3, 2023 at 14:47
  • @Joachim Ah, but the other 8 billion people of the Earth, let alone the non-human population, didn't object. To lead a more harmonious life demands a lot more tolerance, and, then, acceptance. Apr 4, 2023 at 6:53
  • @Nuclear Hoagie Ah, but the other 8 billion people of the Earth, let alone the non-human population, didn't object. To lead a more harmonious life demands a lot more tolerance, and, then, acceptance. Apr 4, 2023 at 6:54
-1

I don't see anything inherently wrong with stating 50% (= 0.5) of something.

50% (= 0.5) of a class of 10 is 5.

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    And if the number of students were 15? Would 0.5 still mean half the class? No, no one would say that.
    – Mari-Lou A
    Apr 2, 2023 at 16:38
  • @Mari-Lou A Technically speaking, where things "go off the rails", say, is giving someone half a pizza. The notion that half isn't 0.5 . Apr 2, 2023 at 16:59
  • Much depends on what you mean by 'inherently wrong'. It is true that using 0.5 for a half is intelligible, and does not violate any generally accepted rule of grammar. On the other hand, it is also true that in some contexts it would appear rather odd, but that there may be some contexts in which it would not. What the question calls for is an account of when it would be odd (even if not, strictly speaking, wrong) and when it would not be.
    – jsw29
    Apr 2, 2023 at 20:46
  • @jsw29 ...which is what I gave in my answer, although you seem to have some sort of objection to it.
    – Andrew Leach
    Apr 3, 2023 at 15:12
  • @AndrewLeach, there seems to be some confusion here. My comment on your answer was posted below your answer; the comment I have posted here was directed at a different answer. You and I agree that 0.5 is usually odd, but not incorrect; what we disagree about is whether the oddness is due to what you perceive as its excessive precision.
    – jsw29
    Apr 4, 2023 at 16:01

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