Hello! I would say it depends on the situation. In everyday speech, we stress the first syllable. However, if we really want yo stress that something absolutely cannot be, we will stress the second syllable. I hope that helps.

Cannot is 3 times more common than can not (as separate words). Both are acceptable. As to pronunciation often the second syllable is stressed, yes. It's your choice. Perhaps the best thing is to contract it down to CAN'T when speaking! One syllable. End of problem. When it is used as two separate words, as in, Peter can not only run one hundred yards in 10 seconds, he can also sing while doing it..... again it's choice but probably the 'not' gets the stress or the 'can' and the 'not' get equal stress.

cannot = CANnot can not = canNOT

Hello XiaoKaoy: I do not know if there is a simple explanation for this practice of sometimes emphasizing the First syllable as in "CAN-not," and other times emphasizing "can-NOT" in the use of cannot. The human voice, in speaking will sometimes Rise in pitch and strength when the meaning requires that the emphasis be on the CAN. In other situations, the meaning requires emphasis be spoken so that it is on the second syllable NOT. If I can speak to you on Skype, I can show you the difference. In Text, it is most difficult to show you the distinction. If I am refusing to do something, I can put the emphasis on the first syllable, saying; "XiaoKaoy; I CAN-not drive you clear across town this afternoon. I have too much work to do here!" That may sound clear or seem clear; but at the same time, I can emphasize the second syllable to you in dialogue, and say also; "XiaoKaoy; I can-NOT drive you clear across town this afternoon. I have too much work to do here!" So....what can we learn from this? What it means that the different pronunciations show that in at least one instance, the rule for pronunciation is not being followed. So what you have is a kind of "slang" usage for "cannot". All it shows, no matter which syllable has the emphasis, is that somebody is not going to do something and they are telling about it with a bit of a strong feeling to show you the finality of their decision. Basically, this means you do not have to worry about it. If you speak the word cannot, with a balanced emphasis, equally on both the first and second syllables, your communication will be clear and precise, and whoever hears you will understand your meaning without question. You can say; "Bruce, I cannot drive you clear across town this afternoon. I have too much work to do here. You will have to take a Taxi." So you see, it is not a problem at all. Just balance your pronunciation equally, and say "cannot" in even tones and strength, and your use will be fine. .