I understand the phrase "only child" means the only person born from or adopted by a set of parents in a family, or a person with no siblings. I often hear the term used as "an only child," which does not appear to be grammatically correct, but does appear to be the correct usage of the term. I have sometimes used "the only child" instead. Which phrase is correct? Is "the only child" incorrect?

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    Why was this downvoted? – bwDraco Jul 13 '11 at 18:58
  • I didn't downvote it, but I did find myself upvoting all 4 answers because they're all perfectly good. Maybe somebody thought a question so easily answered isn't a particularly good question. Though I've no idea what that implies for whether it's easily established from standard online resources. – FumbleFingers Jul 13 '11 at 20:46

X is "the only child" of his parents, and "an only child" along with Y and Z. Similarly, I am "the" elder child of my parents and "an" elder (and eldest) child along with bunches of other people.

One refers to the specific situation; the other refers to the classification.

Edited to add:

Consider the following examples:


Census interviewer: Do your parents have any other children besides you?
Teenager: No, I'm the only child.


Bob: I'm an only child.
Sue: You too? Did you also experience (...)?

Now what happens if Bob says "the" instead of "an"?

Bob: I'm the only child.
Sue: Gee, I thought you were an adult.
Bill: There are several children in this room.

Bob can correct this problem with the somewhat cumbersome phrase:

Bob: I'm the only child of my parents.

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    +1 for correctly drawing the distinction in your first sentence. I think you'd get more up-votes if you explained your reasons in a little more detail. – Robusto Jul 13 '11 at 18:04
  • Thanks @Robusto. Better? – Monica Cellio Jul 13 '11 at 18:36
  • I think your vote tally speaks for itself. ^_^ – Robusto Jul 13 '11 at 18:39

Although at first glance "an only child" sounds ungrammatical, in fact "only child" is a noun in and of itself. From the Cambridge online dictionary:

only child, noun (plural only children)

Definition: a child who has no sisters or brothers

As for using "the only child", I don't see why it would be considered incorrect. In a different context, one might say "the only jar on the shelf". Your version of the phrase is grammatical, but the compound noun above is the one people may be expecting in that given context.

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An only child refers specifically to a person who has never had any brothers or sisters. The only child is more general; it refers to the sole child belonging to a particular group or satisfying particular criteria, which must be specified.


John is an only child. He is the only child of James and Susan.

Mike is the only child in the room right now. That does not necessarily mean he is an only child.

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  • I think you mean "the only child" is more specific, not more general, as it refers to a specific family. – Barry Fruitman Jul 14 '11 at 4:31

"An only child" implies that the person is the only child of their parents. The use of the indefinite article identifies the person as belonging to the subclass of children who have no siblings.

"The only child" also generally implies "of my parents", but it requires a qualifier, and is thus context-dependent. You could also be "the only child" in a group consisting almost exclusively of adults, or in a dystopian future someone could be "the only child", period; that is, the only person of young age in existence on the planet.

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    I disagree that "The only child" implies "of my parents", unless the discussion has already set the context. Otherwise it implies to me that we are talking about an actual child, of which there is only one (in the room, etc) and not "a person with no siblings". – Mr. Shiny and New 安宇 Jul 13 '11 at 20:16
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    If you say "I'm the only child", by itself, you have pretty much established the context, as there are very few contexts that would make sense. I did say the term is context-dependent, requiring a qualifier, but in absence of a more fitting context "of my parents" is generally assumed. Nobody in their right mind would hear that and think you were the only person of minor age on the entire planet, which is what it would mean literally. – KeithS Jul 13 '11 at 20:38
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    In the absence of more context, I'd assume by default that the context is the general area. If a kid came up to me and said "I'm the only child", I'd most likely look around for a playmate than consider the implications of not having siblings – 3Doubloons Jul 14 '11 at 12:50
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    @KeithS: "I'm the only child", by itself with no other context, suggests to me that the speaker is a child, and is unique in that regard. It's impossible to know if the speaker has siblings, since they may not be present, or may be grown-ups, etc, whereas "I'm an only child" can only mean "I have no siblings". – Mr. Shiny and New 安宇 Jul 14 '11 at 13:43

I think what we are missing here is that we have refused to realize both words. An is indefinite while the is definite.

But using it with a child simply means we both know HE or SHE is the only child. If you say an only child, you have generalise the term to mean that you are an only child AMONG many other similar issue in other families. It just means GENERAL..

But the only child on the other hand is specific and definite. If i try to pick point someone among many, i can say THAT'S THE ONLY CHILD OF THE FAMILY.. it won't be okay then to say THAT IS AN ONLY CHILD OF THE FAMILY as i am trying to identify someone in a way.

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