can and can't

Dictionaries list the pronunciation of can as [kʰæːn]. However, in reality, this is just one of its many pronunciations — and not the most common. The fact is that both can and its negative form can't have several pronunciations in actual speech.

1 can 

a) When can is used on its own with no object, it's commonly emphasized and given its full pronunciation [kʰǽːn]. Note that you may also hear people pronounce stressed can as [kʰɛːn].

I'll go if I can. [ɑɫgòʊ̯ ɪfaɪ̯kʰǽːn/kʰɛːn]I can if you want me to[aɪ̯kʰæ̀:n ɪfyuwɑ́nt̚.mitʰu]

b) When can is followed by a verb or other word in a neutral utterance (not emphasized), it's normally reduced to short [kʰɛ̣n] (the underdot indicates no word stress within the utterance).

I can ask him tomorrow. [aɪ̯ɛ̣næ̀skǝm tʰǝmɑ́roʊ̯]I can also text you.[aɪ̯kʰɛ̣nɑ̀ɫsoʊ̯ tʰɛ́kst̡t̡yu]

Nina's going over the RSVPs for her upcoming wedding and notices that one of her friends has declined her invitation.

____________

Nina: Bobby, I just saw your RSVP… you can’t come to my wedding?

Bobby: I can come — I just don’t want to. I don’t want to be anywhere near my ex-wife and her new husband. 

____________

Here, can is emphasized by the speaker in order to insist, so, naturally, it has its full pronunciation.

c) Especially in rapid speech, very often American speakers will reduce the already reduced form [ɛn] to [kʰɴ] as in I can tell you  [aɪ̯kʰɴ tʰɛɫyu] in the following example. Here, [ɴ] stands for syllabic [n]: an n-sound acting as the vowel in this word. (See Vowels)

I don’t know why people are so gung ho on the idea of going to Mars. I can tell you this — they’ll have to make at least a thousand successful trips before I even consider getting into a spaceship!

d) Especially after a word ending in a vowel sound, many Americans will pronounce reduced [kʰɴ] with an initial [g] sound: [gɴ]. This can be easy to miss since it amounts to little more than a sort of short gulp, so you have to listen very carefully for it.  For example, If you can tell me...  [ɪfyu.tʰɛɫmi]

Note that the final /n/ of [kʰɛn] [kʰɴ] and [gɴ] assimilates to a following velar or labial consonant:

(i) In front of the velar consonants [g k], /n/ is pronounced [ŋ] or syllablic [Ŋ] — both pronounced like the -ng in sing. 

____________

I can call you later. 

[aɪ̯kʰɛŋkʰɑ̀lyu léɪ̯ɖʀ]

[aɪ̯gŊkʰɑ̀lyu léɪ̯ɖʀ]


We can go tomorrow

[wikʰɛŋgòʊ̯ɖǝmɑ́roʊ̯]

[wigŊgòʊ̯ɖǝmɑ́roʊ̯]


(ii) In front of the labial consonants [b p m], /n/ is pronounced [m] or syllablic [M]:

____________

I can buy it online.

[ai̯kʰɛmbàyɪɖɑnlá:n]

[ai̯gMbàyɪɖɑnlá:n]

I can put another steak on.

[ai̯kʰɛm.pʰʊ̀ɖǝnǝðʀ stéi̯kɑn]

[ai̯gM.pʰʊ̀ɖǝnǝðʀ stéi̯kɑn]

I can make you a steak.

[ai̯kʰɛm.mèi̯kyuwǝstéi̯k]

[ai̯gM.mèi̯kyuwǝstéi̯k]

In this snippet, you'll hear examples of all three endings: 
he can count [higŊ.kʰæʊ̯nt̚] he can print his name [higM.pʰrɪnɪzneɪ̯m]he can speak English and Spanish [hi.spikɪ̀ŋglɪʃ ɛnspǽːnɪʃ]

My little boy’s only three years old and already he can count to a hundred, he can print his name, and he can speak English and Spanish. 

2 can't

a) The negative form can’t differs from can in pronunciation, of course, with the addition of final [t], but there’s another more important difference; even in a neutral statement, can’t almost always has a secondary stress. In other words, it’s stressed, but it's not the most stressed word in the utterance — another word always has the primary stress and it's usually the verb that follows.

In this snippet, notice that every occurrence of can't has a secondary stress. In other words, it's not the most stressed word in the sentence, but unlike can, which normally has no stress, can't is stressed and the [æ] has its canonical pronunciation, as in catAlso note that in front of words beginning with a consonant, the final [t] isn't released and the whole word is significantly short. This isn't the case with can't in front of a vowel. (See (b) below)

Bobby: I can’t believe how fast your tulips are growing! I can’t͜ understand why mine are growing so slowly.

Jim: I can'imagine. You can't water them every day. They can’t͜ absorb that much water. Water them once a week — you can't go wrong.

b) When can’t is followed by a word beginning with a vowel, things can get a little complicated for the non-native ear. In very careful speech, you might hear someone pronounce I can’t imagine as [aɪ̯.kʰæ̀nt͜ ɪmǽːǧɪn], with a very light [t] and a short ]

However, the vast majority of American speakers will swallow the final [t], as is common with words ending in -nt, and say [aɪ̯.kʰæ̀n͜ ɪmǽːǧɪn] with a slightly longer [æ]. Since this theoretically sounds like can, the only indicator that it's actually negative is the secondary stress.

In other words, in front of a vowel, we'll pronounce can’t like can and still be understood to mean can’t. How is that possible? The key is the stress. Remember that in neutral utterances, can is pronounced with practically no vowel and is unstressed. However, can't has a secondary stress. 

Listen to I can imagine and then I can't imagine

Listen to Bobby and Jim's conversation about the tulips again, and note the pronunciation of the phrases can't understand, can't imagine, can't absorb.

3 cannot

a) You may have been taught that cannot is just a more formal version of can’t. However, there's more to it than that. First let's look at its pronunciation, and then talk about usage.

Cannot can be pronounced in one of three ways: the first syllable may be stressed, in which case it's simply pronounced [kʰǽ(:)nɑt̚] Alternatively, the second syllable may be stressed and the first vowel pronounced as [æ] or [ɛ] or even [ɴ]: [khænɑ́t̚] [khɛnɑ́t̚] [kʰɴ.ɑt̚]

Additionally, some speakers may double the [n]: [kʰænnɑ́t̚], [khɛnnɑ́t̚] [ɴ.nɑ́t̚]

In terms of usage, although cannot may be used as a formal equivalent of can't, it has another important role: cannot (or can't) is used instead of can not, where it's not the modal can that's being negated, but rather what follows not. For instance, the statement You can't/cannot go means You are not able/allowed to go. However, You can not go means You have the option of not going. 

Nicky wants to take his family to the beach, but he has to give his son a little "encouragement" to join them.

___________

Nicky: Alex, put on your swimming trunks — we're about to leave.

Alex: I don't want to go. I think I might just hang out here.

Nicky: Do you now! Well, you have two options: you can not go to the beach with us, in which case you'll have to mow the lawn, or you can go with us and mow the lawn next weekend. The choice is yours.

Alex: Yeah... let me put on my shorts.

Nicky: That's what I thought. Good choice!

b) Although cannot is a formal equivalent of can't, it does have its place in conversation and everyday speech. For instance, sometimes teachers and parents choose to speak very formally to their children when they want to sound official and categorical. For instance, in the snippet below, Nicky wants to make it clear that he can't, under any circumstances, tolerate certain behaviors.

Nicky finds out his teenage son came home drunk last night and is in his room with a hangover.

____________


Nicky: Are you awake?

Bobby: Ugh, can we talk later? 

Nicky: No, we cannót! I hope last night was worth it, young man, because you're not going to see Dougie or Ray outside of school for a month. I want you to come straight home from school and I'm going to have a list of chores for you to do around the house. And I'm going to call their parents and let them know what you three got up to last night. Even though I can imagine they're in the same state you are.

Bobby: What?! Dad, please!

Nicky: Please nothing! I cánnot and will not tolerate drinking in this house! And don't let me find out you drove everyone home last night in that state!

____________As you can see, the father pronounced cannot two different ways in this snippet. In the first one, he's purposely stressing the syllable not in order to be categorical. In the second instance, he stresses the first syllable to match the stressed will that follows.