I often see people write “can not” where they actually mean “cannot.” I have tended to dismiss this as a spelling error, but a sentence I encountered today made me look a little deeper into the matter. Here, I simplify that sentence: “We should do everything we can not to raise taxes.” In this sentence, we cannot substitute “cannot” for “can not”—the unrelated words “can” and “not” are juxtaposed rather by accident.
In fact, “cannot” is the negative form of “can,” and the only thing that can be substituted for it directly is the contraction “can’t.” Consider this sentence: “We cannot raise taxes.” This sentence has the meaning either that we should not raise taxes or that we are incapable of raising taxes. But what happens if we substitute “can not” for “cannot”? We get this sentence: “We can not raise taxes.” This sentence might have slightly different connotations depending upon the context, but the basic meaning is nearly the opposite of one of the meanings of the corresponding sentence containing “cannot”—it means that not raising taxes is an option, but the implication is that raising taxes is an option, perhaps the most obvious or likely one.
Think carefully when next you are tempted to write “can not.”