After the therapy, eight children (43%) became able to crawl/move on their back.

Or should I use "on their backs"?

Singular because each child only has one back, or plural because we're dealing with eight backs?

  • 6
    Related: “Only those who qualify will be awarded a certificate” or “Only those who qualify will be awarded certificates”? and the many linked questions on the right hand side of this page.
    – RegDwigнt
    Commented Mar 6, 2011 at 16:56
  • I'm more puzzled by the sample size of 18.6 children.
    – Phil Sweet
    Commented Jul 21, 2020 at 18:58
  • A key aspect of this one is that elements of an experiment are supposed to be independent. Granularity is inherent in experimental design. Thus there were eight separate events of a child crawling on their back. Contrast this with a business closing causing 25 people to lose their jobs. I don't think it matters much whether the agreement issue crosses a prepositional phrase or clause boundary. The inclusion of the percentage value may well confuse the matter of event discreteness.
    – Phil Sweet
    Commented Jul 21, 2020 at 20:22
  • These constructions are often variable, the tendency to use the singular becoming more marked with more fixed phrases. All the books you have been issued have a receipt in the back, which you must sign and hand in. Commented Nov 14, 2020 at 15:45

3 Answers 3


Plural, because we are, in fact, dealing with eight little backs. And a back is a back, no matter how small. A child has a back, but children have backs.

I'm sure others will back me on this.

  • 1
    Not relevant - if several children owned a single turtle between them, it would be "their turtle", not "their turtles". Commented Mar 6, 2011 at 17:49
  • @user653: But the OP is not talking about a shared turtle.
    – Robusto
    Commented Mar 6, 2011 at 18:01
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    @Robusto, I think the point @user653 was making is that the fact that "their" is plural does not automatically imply that the word following it has to be plural too.
    – Hellion
    Commented Mar 6, 2011 at 18:24
  • @Hellion: Ah, I see. @user653 must be responding to @Fountain, not to my post itself.
    – Robusto
    Commented Mar 6, 2011 at 18:31
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    @Robusto: also, you forgot to mention that while children have backs, baby got back. :-)
    – Hellion
    Commented Mar 6, 2011 at 18:46

The semantic, grammatical, and logical arguments clearly suggest it's 'correct' to use the plural, and that's what most people do.

However, despite the fact that I doubt if any style guide endorses the singular, it seems that about 10% of usages for back persist in using the singular.

For reasons which escape me, that 'incorrect' minority rises to nearly 25% when the body part in question is chest. In both cases the evidence strongly suggests the incorrect usage is becoming more widespread.

Personally I believe it's a situation where grammarians backed the wrong horse, and their blind prescriptivism will eventually be defeated. People quite naturally want to use the singular when the number of [body parts, whatever] is immaterial, and only the plurality of [babies, people] is relevant. Increasingly, it seems, they're prepared to do this even at the risk of being considered illiterate. .

  • Great explanation fumble. So, you are saying that it is more natural to use the singular in this case in spite of the grammatical rule, right? Commented Aug 19, 2019 at 23:33
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    In that graph, we have no idea of the surrounding context in which the words "on their chest" and "on their chests" are in. This question is about when the subject is plural. So it is possible that people merely discuss individuals on their chest often which tilts the data when discussing plural subjects.
    – Noah
    Commented Jul 14, 2020 at 16:55
  • Try get something off their chest / get something off their chests. But the distributive plural vs distributive singular question has already been well covered. Commented Feb 1 at 19:29
  • @EdwinAshworth: This was a while ago now, so there's no chance I can remember exactly what I was thinking when I wrote this answer! I see no evidence in my text above to suggest that I gave any serious consideration to the matter of how many of the charted instances might be singular "they". But now I immediately think the reason the chart for get something off their chest/s looks somewhat different to the chart in my answer is probably down to the fact that multiple people might have something / be on their chest/s, but get something off your chest is usually a "solo" act. Commented Feb 1 at 20:43
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    Rappaport's analysis looks authoritative. Commented Feb 1 at 23:29

It is decidedly the Singular Back. This is because it is the therapy that is being evaluated but the results are singular. The children are not grouped or lined up as in a race to see who can move. The plural children is only used to describe the percentage of those who are able to move. Each child moves only on his or her own back, no other, Singular.

  • From a logical standpoint, I would support singular, but language is not always logical. Suppose it was one child. You would still use 'their' as in "After the therapy, one child became able to crawl/move on their back". So this can clearly be the singular they/their. Dutch will use singular in this setting (for the mentioned reason in this answer), but my English feeling says 'plural'. My guess is that language is fuzzy here and that grammar professors will have a firm opinion, which may or may not reflect reality.
    – gctwnl
    Commented May 26, 2023 at 20:44
  • No. The distributive singular and distributive plural are both acceptable. In individual cases, one or the other will be more popular, but patterns are complicated (see the duplicate). Commented Feb 1 at 19:31

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