If you look up “cannot” in the dictionary, the definition usually says “a form of can not” or an “incapacity, inability or withholding permission.” From this, it is easy to assume that both spellings are correct. Technically speaking, the two spellings are interchangeable; however, modern convention and preference use the spelling “cannot.” Most modern word-processing software even highlights the use of “can not” as grammatically incorrect. In addition, specific style guides may give the distinction for this preference as well. When writing for Write.com, always use “cannot” rather than “can not.”
Many people argue that the definition of “cannot” is very literal, meaning that the possibility of doing something is not there. With this in mind, it is argued that “can not” is the correct choice when the possibility of doing something is there. However, even when a choice is present, the most accepted spelling is “cannot.” Consider the below example:
Example: She (cannot/can not) study anymore after six straight hours of doing it.
While the context of the above example implies that “she” could study more if she wanted to but is choosing not to study, “cannot” is still the preferred spelling.
Sometimes it is more acceptable to use “can not.” Usually this is true when the “not” is emphasized or used to show the implicit choice. Consider the following example:
Example: She can drive, or she can not drive.
In the above example, the use of “can not” implies that “she” has a choice. She can choose to drive, or she can choose not to drive. While this falls under the argument for “can not” from above, the distinction lies in the emphasis and the shown differential between the two clauses.
Most contractions represent the joining of two words. “Can’t” is an exception however. Following the rules that apply to most contractions, you probably find yourself tempted to replace “can’t” with “can not.” However, when replacing “can’t,” use “cannot.”
“Can’t” is usually acceptable in all forms of informal writing, so if you struggle with choosing between “cannot” and “can not” or the use of “can not” is something you favor, you can avoid the choice by using “can’t” when writing informally. On the other hand, the use of contractions is often frowned upon in more formal writing. Some style guides may even restrict the use of contractions. For example, when writing for Write.com, always spell out the words instead of using contractions. This means using “cannot” instead of “can not” because of the style preference for “cannot.”