Modal Auxiliaries

Modal Auxiliaries
These auxiliaries add to the verb a special semantic component such as ability, obligation, possibility. Some of the modal auxiliaries express the same kinds of semantic coloring as verbs in the subjunctive mood (note the relationship between modal and  mood).
Modal auxiliaries generally have no-s suffix for third person, and no infinitive or participial form. They have two formal tenses, the present and the past, which are used with the simple form of the lexical verb (may offer, might offer), the progessive form (may or might be offering), the perfect form (may or might have offered)

Example :

a. Can and May
- Can I borrow your car?
- May John come to the movies with us?

b. Should and Ought To
- You should do your homework every day
- She ought to eat less if she wants to lose weight

c. Must and Have To
- I must save some money every week
- This is an execellent book. You have to read it