What is the difference between "can not", "cannot", and "can't"?

Question

From what I've learned "can't" is just short for "can not", but I never really understood the difference between these three. Can someone explain to me?

Answer 1

The words "cannot" and "can't" only mean "not able to."

The phrase "can not" may mean "cannot" or "can't," but it also may mean "able not to," which is much different than "not able to" as it conveys the ability to not do something rather than the inability to do it.

The contraction "can't" only ever means what "cannot" means, so it doesn't mean "able not to" but only means "not able to." The word "can't" is a contraction of "cannot" and of "can not" but only of "can not" when "can not" means "cannot" and not when "can not" means "able not to."

Because "able not to" is only expressed by "can not," not by "cannot" or "can't," most style guides require that "can not" only be used to mean "able not to" in order to eliminate confusion with "cannot" and "can't." When "not able to" is what is meant, most style guides require using "cannot" or "can't," never "can not."

Examples:

• "I can't go" means I am not able to go or I don't have permission to go.

• "I cannot go" means I can't go.

• "I can not go" means either I am not able to go (i.e., I can't go) or I am able not to go.

Since the third example's two possible meanings contradict one another, one meaning expressing an inability to go and the other meaning expressing an ability not to go and thus also implying an ability to go, this creates confusion. Therefore, it has become conventional in writing, even required by many style guides, to use "can not" only to mean "able not to" and never to mean "not able to," never to mean "cannot" or "can't," though "can not" technically still does have that meaning.

Additional Example:

"John, come to the party with me," pleaded Jane.

"Party? No, I can't go," responded John.

"Please!"

"No, I cannot go. I've got too much homework. In fact, I was really hoping you'd be able to help me because it's way over my head and I don't know how else I'll get through it."

"Well, I suppose I can not go and stay here and help you instead, but you owe me a night out."

In the above example, "can't" is used to mean that John's not able to go to the party, "cannot" is used to more emphatically reiterate that John's not able to go to the party, and "can not" is used to mean that Jane is able to not go to the party, that she has it in her power to stay home and help John instead of going to the party, but she still can go to the party, like if she changes her mind about helping John instead, so "can not" there doesn't mean that she can't go to the party, only that she's able not to.