In this video, learn the difference between: 'cannot', 'can not' and 'can't'. Cannot is the negative form of the verb can. Simply replace 'can' with 'cannot' to make the sentence negative. Notice how 'cannot' is one word, with two n's. Can't is the contracted form of 'cannot'. You can think of it as the short form. To use it, simply replace 'can' with 'can't' to make the sentence negative. 'Can't' is the most common choice in American English and using it will help you sound fluent and natural.