What to Know Both cannot and can not are perfectly fine, but cannot is far more common and is therefore recommended, especially in any kind of formal writing. Can't has the same meaning, but as with contractions in general, it is somewhat informal. In some cases, the not following can is in fact part of another phrase, such as “not only"; in such instances can not is the appropriate choice. CANNOT definition: 1. the negative form of the verb "can": 2. used to say that something will certainly happen: 3…. Learn more. ‘ cannot ’ is the unabbreviated form and is preferably used in formal language or for particular emphasis: “Unfortunately, we cannot accept your offer.” Such a sentence may be found in a more formal email. “This cannot be true!” Here, the statement is strongly confirmed by the use of the regular (long) form. This guide will help you discover which is the correct one to use; cannot or can not .
