2. Modal verbs are helping/auxiliary verbs that express ideas like ability, necessity, and prohibition. Many modal verbs have more than one meaning. They are always followed by the simple form of a verb.

3. HAD BETTER o 'D BETTER OUGHT TO SHOULD SHOULDN´T

4.  We can use 'must' to show that we are certain something is true. In general, must expresses personal obligation. Ex. We must show our passport at the airport We often use have to to say that something is obligatory. In general, have to expresses impersonal obligation Ex. John has to wear a tie at work. Children have to go to school We can use need to say something is necessary or unnecessary Ex. You usually need to chec k in at least two hours before a flight leaves. I don’t need to take a raincoat

5.  We use “ had better ” to give advice about specific situations, not general ones. Ex. You'd better tell her everything. Is used to advise or make recommendations. also expresses assumption or expectation as well as strong probability. Ex. You ought to stop smoking. R ECOMMENDATION This stock ought to increase in value. PROBABILITY We often use should when offering advice or opinions. Ex. You should see the new James Bond movie. It's great!. People should worry more about global warming.

6. http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/3 30-modals-necessity1.htm