TENSES

     A sentence we would not expect to Read in English would be: "I saw him tomorrow." And you could give two explanations. You could say that "Tomorrow" should be changed to something like "Yesterday" or "last week";or that "saw" should be changed to "will see". These are yet more rules of English, and they concern the relationship between the tense of a verb and related adverbs.
     By now, you may have noticed that when we talk about rules, we often mean making things agree with each other.
We have to do the right thing, otherwise there will be chaos. But rather than reffering to These matters as 'rules' ,It is sometimes easier to see them as 'costoms'.
     But when we talk about the customary way of speaking a language we're not Just talking about grammar: we're also talking about pronunciation, for example. When you listen to speakers of English on television, you can usually understand the people who speak like your English teachers, but others are very difficult to understand.