Verb be can be contracted with a subject or the negative adverb not. There is no difference in meaning between these phrases. Uncontracted: I am not happy. You are not late. She is not smart. We are not hungry. They are not young. Contracted: I'm not happy. --- You're not late. You aren't late. She's not smart. She isn't smart. We aren't hungry. We're not hungry. They're not young. They aren't young. / Nothing new , but it's necessary to remember these lessons, because it's one of the basic grammar at English language. / If I were you , I'll teach it the way you do..