They don´t take ` –s/ -es´ in the third person. She cans play the piano beautifully. They are followed by an infinitive without `to’. She should to eat more vegetables. They function like auxiliaries in Negative and interrogative sentences. Can you speak louder, please? Do you can speak louder, please? You shouldn´t talk like that. You don´t should talk like that. They have no –ing, infinitive nor past participle forms. canned canning to can They provide additional and specific meaning to the main verb of the sentence. You mustn´t drink that water, it´s dangerous. They don´t have all tenses. They use other verbs to do that Can Be able to Must Have toTo express present ability:She can play the guitar To make a request:Can I borrow your pen? To offer to do anything:Can I help you? To ask for permisssion:Can I leave earlier? Yes, you can. To express possibility or impossibility:Learning a language can be a real challenge It can´t cost more than a dollar or two. To express past ability: Nancy could ski like a pro by the age of 11. To express possibility:Extreme rain could cause the river to flood the city. To make suggestions:You could see a movie or go out to dinner To make a request:Could I use your computer to email my boss? In conditional sentences:We could go on the trip if I didn´t have to work. To express Obligation: You must obey the rules. To express necessity: Students must pass an entrance examination to study at this school. To express certainty: This must be the right address!. To express prohibition:Jenny, You mustn´t park there! ( PRESENT, PAST, FUTURE ) To express Obligation:He has had to leave early. To express necessity:The soup has to be stirred continuously to prevent burning To express certainty: This answer has to be right. To Advise:You should focus more on your family and less on work. To recommend:When you go to Berlin,you should visit the palaces in Potsdam. To express expectation:By now, they should alrady be in Dubai. To express Obligation:I really should be in the office by 7:00 a.m To offer:Would you like some tea?. To invite:Would you like to go to the cinema? To express repetition in the past:When I was a kid, I would always go to the beach. To express Possibility:It may rain tomorrow To make a request (formal): May I open the window, please? Give permission: Johnny, you may leave the table when you have finished your dinner. To express possibility: Your purse might be in the living room. To make a request ( very formal): Might I borrow your pen? To make suggestions: You might visit the botanical gardens during your visit.