Q: I have questions about “cannot” and “can not.” Is there a difference? If so, then how is each to be used? If not, which is the preferred usage?
A: The short answer is that you’ll almost always be right with one word and wrong with two.
The Oxford English Dictionary defines “cannot” as “the ordinary modern way of writing can not.”
There are only three situations in which it would be correct to separate the “can” and the “not”:
(1) when you want to emphasize “not”: “Maybe you can spend $500 for an opera ticket, but I most certainly can not.” (This would be better written as “… but I most certainly canNOT.”)
(2) when “not” is part of another expression (like “not only … but also”): “She can not only hit high C, but also break a glass while doing it.”
(3) when expressing an ability NOT to do something: “The true opera fanatic can not fall asleep even after six hours of Wagner.” (This is a rarely used construction. The idea would be better expressed as “can stay awake.”)
Otherwise, the common convention in standard English is to use “can’t” in casual speech or writing, and “cannot” in formal writing.
Interestingly, this isn’t a particularly new usage. There are only five examples of “can not” in Shakespeare, according to RhymeZone’s Shakespeare search tool, but hundreds upon hundreds of “cannot” examples, like this one from King Claudius in Hamlet: “You cannot speak of reason to the Dane.”
In fact, “cannot” apparently showed up in English around 1400, according to the OED, while “can not” didn’t make its first appearance until 1451. And “cannot” appears far more often in the dictionary’s citations.
In Old English, the negative of the verb “can” was ne can, as in this excerpt, circa 1000, from the Gospel of Matthew: Ne can ic eow (“I cannot know you”).
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