Cannot? Can not?

Andrew, a fellow English teacher, writes:
One of my ESL students asked me a question that I could not find an answer to:

Why is "cannot" written as one word?

Just because! I know. But perhaps there is a better answer? I defer to your experience. Admittedly, it is a question that has haunted me for some time.

I've often wondered the same thing, so this question got me moving—toward my dictionary. There I find that "cannot" is "the negative of the auxiliary verb can: written can not for emphasis."

So I speculate that at some time in the past, people stopped writing "can not" as two words, and the single word became the general usage. Emphasis would fall on the first syllable, as it usually does in two-syllable English words: I CANnot do this.

But I can see how breaking it back into two words would shift the emphasis to the negative: I can NOT do this.

Comments

[Andrew]

I am not sure I understand your response here. I understand the trend towards first syllable stress, but why stick the words together in the first place? We don't write "donot," for example?
Isn't there any reference that we might consult on this question?
Andrew

[Anna]

Hi, I come here again. Hah
I think “cannot” is more polite and more common. When I studied in middle school in China, my English teacher told me “cannot” is more formal that is better than “can not”in English writing.

[Nick]

"cannot" refers to the inability to do something.

"can not" refers to the ability not do do something if one so chooses.

"Can not" is frequently seen used incorrectly (as cannot) in publications such as the The Guardian, which really ought to know better.

[BoggyWoggy]

Well, to add to the discussion, consider this: "can" is a positive. "Not" is a negative. It actually seems quite odd to consider that people can NOT do things. Instead, it might be better to say, "I am not capable," yet, once again, "am" and "not" contridict one another...