The siren song of negativity, the leaning of lassitude, the jargon of just say no, the argot of no got: this word sounds like cant, cant, cant, or cant, but says can it – not can it do something? but just can it! But can it be a word? It’s can plus not, right, so two words, not one, right? No, that’s the point of contractions: two words come together and the contraction gives birth to a new word – the amoeba in reverse. Some may proclaim that can’t isn’t in their dictionaries (the ones in their minds, or else they’ve done a razor job on Oxford), but it’s a word no less (just like ain’t, millions of schoolteachers notwithstanding – ain’t may be a very informal word, a word you can’t – or, more accurately, shouldn’t – say in certain contexts, but it’s a word).
The word seems straightforward enough in sound – voiceless stops at front and back (the latter of which is often reduced to a glottal stop or even nothing, so you often can’t hear it but still know it’s there, partly due to the emphasis this word gets that can may not), the nasal (often reduced to a nasalization of the preceding vowel, with the tongue not touching until the t), and a vowel – but people can’t even get together on that vowel. Canadians and most Americans say the same a as in that (Hall and Oates: “I can’t go for that!”) – whatever vowel that is, relatively open in some dialects and more like “eeyuh” in some – while many other speakers move it farther back to rhyme with want. A characteristic of Boston-area dialects (of the “towny” class) is to use the more front vowel for can but the more back one for can’t, as if it just can’t make it any farther forward. There are a few other words this word sounds like, most of them spelled cant, but also, for instance, Kent, as in Clark or State.
But you can see which word you’re dealing with here thanks to the apostrophe, that little marker that many people can’t quite get a grip on in many places – because you can’t hear it in speech, and because some of the places it’s used have no historical justification (I’m thinking specifically of the possessives, which were not formed from a word plus has, as the misguided sorts who inserted the apostrophe a few centuries ago thought; they’re an inflectional ending that happens to have converged in form with the plural ending and by coincidence sounds like a contraction of has). Me, I’d like to get rid of apostrophes almost everywhere; George Bernard Shaw demonstrated how easily it can be done without harming clarity, and, for that matter, so do all speakers who don’t hook their fingers in the air every time they say a word with one. But language operates by common agreement, and if you make a change like that it might become too distracting from your message, so I probably can’t get away with it…
But you never know. Which, come to think of it, is where can’t comes from: can is formed from the past tense of cunnan, “know”, the source of modern (uncommon) ken. It’s originally a “preterite present” verb, meaning that it took a past tense and made it a present tense: I have known or have learned, so I am able. Now it’s an auxiliary and can’t (in standard English) work with an other auxiliary – we have to say you won’t be able to do that rather than you won’t can do that, even though be able to is just a paraphrase, not another form of the same verb. Not, for its part, comes from nought (and who says nought will come of nought?), which in turn is ne plus aught; ne is the original negator in English, and could often be seen in negative concord – where if one thing in a phrase was negated, the others were as well (he ne shall never do it). But then it was decided by some people in the 18th century that that was a double negative and illogical, and so now you can’t do it. Can you think of a reason to insist that, in spite of all of English’s illogics, one must not violate some mathematical conception of logic in one place, even though it used to work fine and still does in many other languages? I don’t know any. But I still can’t.
But then, when faced with all my whines of “I can’t,” sometimes I find it best to open some wine, decant, and recant.