At any point in history was "Why cannot...?" used as frequently as "Why can't...?" Is it even grammatically correct to say "Why cannot you do this?" I know it can be rearranged to be "Why can you not do this?," but I always presumed the contraction and the contracted phrase could be used equivalently, without changing the sentence structure. I think this pattern holds true with the other question words (e.g. how, when, etc.); however, I also know it is common to say "Who cannot do this?" In general, are there rules pertaining to the uses of contractions in questions?

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    In general, I think it's best to think of contractions as independent words of their own with their own syntactic rules. In most cases, you can replace a contraction with the expansion and vice-versa, but not always.
    – nohat
    Commented Dec 1, 2011 at 20:23
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    Great question, I don't think I've heard Why cannot in my lifetime. Commented Dec 1, 2011 at 21:40
  • @nohat: I don't know how widespread the term grammaticalisation is (I only came across it myself a couple of days ago), but it seems to me this is what you mean when you say contractions can be seen as "independent words". Is that right, and if so is grammaticalisation a suitable term for this phenomenon? Commented Dec 1, 2011 at 21:46
  • It has never been the case that the contraction and the contracted phrase could be used equivalently. Consider, "Are you as sad as I am?" where you certainly can't use "I'm". And, of course "Don't you do that." Commented Dec 2, 2011 at 0:24
  • @DavidSchwartz: Those just sound incorrect in the same way "Why cannot you do this?" does. If I had thought of those examples, I would ask similar questions for them.
    – SWV
    Commented Dec 2, 2011 at 0:40

3 Answers 3


The transition point was about a century ago

Usage of “why cannot” and “why can’t” over time

Note that if we substitute a pronoun (I, he, they) for "why", the transition point comes much later (1980 for "I") – or hasn't even happened yet (all other pronouns). I can't explain why that is, except by pointing out that this very sentence is an increasingly typical usage. Maybe we all tend to be a bit less formal when introducing our own selves into the text.

It's only my opinion, but I think can't (similarly, let's) are examples of grammaticalisation. The contracted form has effectively taken on a "life of its own", leading to a situation where OP is prepared to accept that there may be contexts where can't is "grammatical", but "cannot" (or the equivalent "can not") wouldn't be valid.

Using cannot / can not might be a bit stilted in many contexts now we're so used to seeing the contracted form, but I don't think it's ever ungrammatical.

  • At school we were taught that "can't", "let's", "it's" (for "it is", not confused with "its"), and "...'ll" are always wrong & forbidden. Well, I always had the suspection that at the school they where - old school?!
    – Stephen
    Commented Dec 1, 2011 at 19:20
  • @FumbleFingers: It is disturbing that when I use a simple modification of your query to Google ngrams: books.google.com/ngrams/… that the cutoff point is shown to be the 1840's. I would have thought 'why can you not...' to be a more likely intermediate form. What's up with Google ngrams?
    – Mitch
    Commented Dec 1, 2011 at 21:44
  • I forget the proper name for them, but "helper" words/verbs like can, may, be, have, get, will, would, should and so on really do have a life of their own. They're common everywhere, but particularly in speech, which might help them to "evolve" faster than, say, bog-standard nouns. But the substantive point of my answer is that can not -> cannot -> can't has led to the contracted form being seen as a free-standing syntactic unit. In the original form you could have dropped "you" into the middle of it, but now... well, you just can't. Commented Dec 1, 2011 at 22:03
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    I believe the word you are looking for is "clitic". And that's exactly right -- contractions are words in their own right. They evolve their own rules over time. Commented Dec 2, 2011 at 2:39
  • @David: That's a new one on me. I'll remember it - if only because it's a plausible alternative to clitoric (assuming there is such a word). But I was specifically thinking of those "semi-verbs" that are often just helping the main verb along. Like "are helping" there, which could just as well be "[to] help", except we add a bit of "to be" into the mix to emphasise the ongoing nature of the activity. Commented Dec 2, 2011 at 4:05

Arnold M. Zwicky and Geoffrey K. Pullum have shown that -n't is not just a contraction of not. The two American linguists pointed out that you can say why don't you... but not *why do not you... because you can place one and only one auxiliary before the subject in an interrogative phrase. Don't is a single word while do not are two words. -n't is not a clitic but a negative inflectional suffix.

Cannot is the only negative form that contains not rather than -n't. Theoretically, since it is a single word, you can say why cannot you... without a problem. My theory is that modern English speakers don't want to put cannot before the subject because it contains not and sounds like can not. You definitely cannot say why can not you... with a separate not. On the contrary can't remains a single word, which is why they use it more and more often.

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    There was a time (in the 1700s) when why do not you was not uncommon. I don't know whether it was just in the written language (as an incorrect expansion of why don't you) or whether people actually said it. It sounds terrible today. Commented Jul 19, 2012 at 2:49

If you go to Open Library, a search will turn up 52,223 interrogatives (questions) that begin with "Why cannot" in published English literature and there are over 2 million examples of interrogatives that begin with "Why cannot" on the internet.

Looking at a specific example, "Why cannot we" turns up with 758,000 interrogatives (and 8,064 examples in published literature). There are also many examples of "Why we cannot", but they are not interrogatives.

JForrest explains that 'cannot' is the negative form of 'can', and so 'cannot' should be placed in the same location as 'can' would be in a sentence. Since we can say "Why can we grow taller?", "Why cannot we grow taller?" is a logical and properly written negative. We don't say "Why we can grow taller?" so the construct should not be "Why we cannot grow taller?" The reason is that auxiliaries should come before the subject to make an interrogative.

I argue that the "Why cannot" usage is acceptable because of that rule mentioned by Shinji, above, that "you can place one and only one auxiliary before the subject in an interrogative phrase". Thus, "Why cannot" is acceptable though "Why can not" is not.

I admit that some people argue that the contraction "can't" should be used instead in this case. That option is quite popular - there are 16.6 million examples of can't on google and 90,470 in published literature. It is much easier to type can't, and easier to speak it as well. Contractions generally aren't considered ideal for formal writing, however.

Another alternative that is growing in popularity is the construction "Why can we not" which sees 1.2 million uses online, 9,900 in publication.

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    All such archaic formulations as Why cannot X, Why do not X, Why will not X are obsolete in today's English. They are most often seen when a busybodying editor automatically expands a written contraction, unwittingly rendering the entire construction borderline ungrammatical to speakers today.
    – tchrist
    Commented Dec 17, 2021 at 0:53
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    Hello there, tc. You refer to "such formulations" as including "do not" and "will not", but I explicitly ruled those two out in my post above when I stated that "you can place one and only one auxiliary before the subject in an interrogative phrase". Next, I am an English speaker today and do not consider it ungrammatical, so you should qualify your concluding statement. Please remember, though, that my emphasis is not spoken English, but rather proper written English language. I stated that in oral English people would say "Why can't" instead of "Why cannot". Commented Dec 17, 2021 at 9:06

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