They are incomplete verbs that don't have all tenses like the past participle needed for the passive voice. They use other verbs like "be able to" or "have to" to complete their tenses. They are followed by an infinitive without "to" in most cases and don't require an auxiliary verb in questions or negatives. Examples of common modal verbs are can, may, must, should, and would. The modal perfect tense is formed with a modal verb plus "have" and the past participle to talk about logical conclusions, assumptions, abilities, or regrets regarding the past.

2. They are INCOMPLETE VERBS. They don’t have all the tenses. There is not past participle, so there is not passive. They use other verbs to complete the tenses. - CAN is completed with BE ABLE TO “ They can play the piano.” “ They will be able to play the piano in the future.” - MUST is completed with HAVE TO “ You must come early.” “ You had to come early yesterday.”

3. They don’t have –s in third person singular of the present simple “ He can open the door” “ She must come early”

4. T hey are followed by an infinitive without 'to' in most cases. BUT: NEED takes 'to' when expressing absence of obligation in the negative: You do not need to stay if you don't want to. OUGHT TO is a special case and you must learn it like that. It expresses convenience. Ex: You ought to study more more if you want to pass the exam.

5. They don’t need auxiliary verb in the interrogative or negative form “ Can I help you?” “ We shouldn’t go to the toilet”

6. PROBABILITY/ POSSIBILITY ABILITY PERMISSION OBLIGATION/ ADVICE OFFERS CAN I can play the piano Can I go out tonight? CAN’T She can’t be his mum. She ‘s too young I can’t speak German Can I borrow the car? No, I can’t. MIGHT It might rain tomorrow MAY NOT MIGHT NOT If the bus doesn’t arrive soon, we may not see the start of the film COULD It could rin tomorrow I could already read when I was two Could I see your passport please, sir? MAY It may rain tomoroww May I leave the table? MUST She must be his sister because they look alike. You must leave before the clock strikes twelve. HAVE TO I have to study tonight. SHOULD / OUGHT TO You should see it. It’s excellent. HAD BETTER You had better sleep more. WOULD Would you like a drink?

7. Son modales que se refieren siempre a acciones ocurridas en el pasado. FORMACIÓN: MODAL + HAVE + PARTICIPIO PASADO Ejemplos: It must have been a difficult decision They should have invited her to their wedding

8. MODAL PERFECT USES EXAMPLES MUST HAVE + P.P. Conclusión lógica sobre un hecho del pasado Linda has arrived late. She must have been in a traffic jam MAY / MIGHT HAVE + P.P. Una suposición sobre algo pasado She may / might have taken the wrong bus. COULD HAVE + P.P. Habilidad de haber hecho algo pero finalmente no lo hizo You could have asked the doctor before taking that medicine COULDN’T HAVE + P.P. Certeza de que algo no pudo haber sucedido He couldn’t have gone to the concert because he was doing a test WOULD HAVE + P.P. Quiso haber hecho algo, pero no pudo hacerlo por causas externas I would have gone to the party, but I was too busy SHOULD / OUHT TO HAVE + P.P. Queja de que algo haya ocurrido en el pasado o lamento de que no se haya cumplido lo que esperábamos You should / ought to have warned me earlier SHOULDN’T HAVE + P.P. Crítica sobre un acontecimiento pasado que no debería haber ocurrido He shouldn’t have forgotten about her birthday NEEDN’T HAVE + P.P. No había necesidad de hacer lo que se hizo en el pasado You needn’t have brought anything to my party.