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Is there some rule against ending a sentence with the contraction “it's”?

In conversing with non-native English speakers online, I saw someone type:

Do you know who ****I’m*** ?

This is obviously wrong to a native English speaker, but I don’t know why. Is there a rule that tells when contractions are not allowed?

Here are some more similar examples where the contraction doesn’t work (with the expansion of the contraction in parentheses following each):

  • Can you tell who **I’m* by my voice alone? (I am)

  • Please, tell me who **he’s/she’s/they’re*. (he is/she is/they are)

  • If you want to go to the movie, **we’ll.* (we will)

  • Will you have some? Yes, **I’ll.* (I will)

  • I won’t have any, but tell me if **you’ll*. (you will)

  • I didn’t have the same thing for supper as **you’d.* (you had)

  • Would you like to go? Sure **I’d.* (I would)

  • Thanks to @tchrist, Cerberus, JasperLoy for help coming up with more examples.
    – Spare Oom
    Aug 20, 2012 at 1:18
  • 1
    This is a fascinating question. I'll take a stab: You can't contract an uncomplemented verb. Aug 20, 2012 at 1:52
  • This question has a few more examples, but they are covering the same basic phenomenon. Aug 20, 2012 at 4:44

2 Answers 2


All OP's examples are cases where the verb is stressed. In many/most contexts, this applies where the verb ends the statement (#1 can be recast as Can you tell by my voice alone who I am?).

The most general "rule" I can think of is don't contract anything unless you hear native speakers doing it. Also bear in mind that contractions primarily reflect spoken usage, but many aspects of speech aren't necessarily reflected in written usage anyway. So perhaps the second "rule" should be don't write a contracted form unless you see native speakers using that written form.

  • No stress was intended.
    – Spare Oom
    Aug 20, 2012 at 2:00
  • 2
    @Spare Oom: Whether you "intend" it or not, single-syllable verb forms are invariably stressed unless they're acting as auxiliary/modal components alongside another more significant verb. One (slightly contrived) example contradicting that is when you meet someone you know who's accompanied by someone you don't know. Some (but not many) speakers might say "Hello, John!" to the person they already know, then turn to the other and say "And you're?". But most speakers wouldn't contract there anyway - they'd say "And you are?" (stressed verb form). Aug 20, 2012 at 2:07
  • Where is the stress in the two-word sentence “I’m sure” then? I find it to fall customarily on the second word, not the first.
    – tchrist
    Aug 20, 2012 at 2:24
  • 1
    tchrist, funny you choose this phrase, because it's an excellent example. In this case, choosing the contracted form "I'm" actually changes the nuance of the sentence: The stress for "I'm sure" is the second word, "sure". The message is the choice of the word sure: the best word, the word that I have chosen to describe what I AM is: "Sure." If I spell out the contraction, "I am sure" the message changes ever so slightly. Here the word sure is a given, but what I'm stressing is the state of the sureness: I AM sure. I'm affirming that I really AM sure.
    – Bob
    Aug 20, 2012 at 2:40
  • @FumbleFingers I'd stress your example like this: "Hello John!" turning to second person: "And you are?" The way you've stressed it would be a possible response to "You're not the Pope": "And you are?"
    – CJ Dennis
    Dec 6, 2014 at 2:34

You can use contractions when:

It is a subject + auxiliary. (He's, they're)

A negative with not. (Isn't, didn't)

A wh- with is. (Who's, where's)

'Will' is little different as it can be contracted withe a subject pronoun (she'll) or a wh- (who'll).

  • That doesn't explain why *"I'm not a lawyer, but he's" and *"I'm not a lawyer; who's?" are wrong. Aug 20, 2012 at 4:55
  • Yes it does. In both of those, the 'is' is a main verb, so it should not be contracted. Aug 20, 2012 at 7:30

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