Modal Verbs of Obligation

We can use have to + infinitive, must + infinitive and should + infinitive to express obligation (something you have to do).

Present	Positive	Negative
have to / don’t have to	strong obligation (possibly from outside) Children have to go to school. (sometimes ‘have got to’)	no obligation I don’t have to work on Sundays. You don’t have to eat anything you don’t like.
must / mustn’t	strong obligation (possibly based on the speaker’s opinion) I must study today.	negative obligation You mustn’t smoke here.
should / shouldn’t	mild obligation or advice You should save some money.	mild negative obligation or advice You shouldn’t smoke so much.

Be careful about the difference between mustn't and don't have to!
Mustn't means it's not allowed, or it's a bad idea:

You mustn't eat so much chocolate, you'll be sick

Don't have to means you don't need to do something, but it's fine if you want to do it:

I don't have to get up early at the weekend
(of course, if I want to get up early, that's fine, but I can stay in bed if I want

Past	Positive	Negative
had to / didn’t have to	obligation in the past I had to go to wear a school uniform when I was a child.	no obligation in the past We didn’t have to go to school on Saturdays.
must*	changes to 'had to'	-
should have + pp / shouldn’t have + pp	a past action which didn’t happen: the advice / regret is too late You should have gone to bed earlier, now you have missed the train.	a past action which didn’t happen: the advice / regret is too late You shouldn’t have taken that job., it was a bad idea.

* Remember ‘must have done’ is a modal verb of deduction or speculation, not obligation in the past. For example: Julie must have left. Her coat’s not here.

EXERCISE ONE
EXERCISE TWO
EXERCISE THREE

Form

Present Perfect Simple	Present Perfect Progressive
irregular verbs: form of 'have' + 3rd column of irregular verbs Example: I / you / we / they have spoken he / she / it has spoken regular verbs: form of 'have' + infinitive + ed Example: I / you / we / they have worked he / she / it has worked	form of 'have' + been + verb + ing Example: I / you / we / they have been speaking he / she / it has been speaking
Exceptions
Exceptions when adding 'ed' : when the final letter is e, only add d Example: love - loved after a short, stressed vowel, the final consonant is doubled Example: admit - admitted final l is always doubled in British English (not in American English) Example: travel - travelled after a consonant, final y becomes i (but: not after a vowel) Example: worry - worried but: play - played	Exceptions when adding 'ing' : silent e is dropped. (but: does not apply for -ee) Example: come - coming aber: agree - agreeing after a short, stressed vowel, the final consonant is doubled Example: sit - sitting after a vowel, the final consonant l is doubled in British English (but not in American English). Example: travel - travelling final ie becomes y. Example: lie - lying

Use

Both tenses are used to express that an action began in the past and is still going on or has just finished. In many cases, both forms are correct, but there is often a difference in meaning: We use the Present Perfect Simple mainly to express that an action is completed or to emphasise the result. We use the Present Perfect Progressive to emphasise the duration or continuous course of an action.

Result or duration?

Do you want to express what has happened so far or how long an action has been going on yet?

Present Perfect SimplE	Present Perfect Progressive
Result (what / how much / how often) I have written 5 letters. / I have been to London twice.	Duration (how long) I have been writing for an hour.

Certain verbs

The following verbs are usually only used in Present Perfect Simple (not in the progressive form).

state: be, have (for possession only)

Example: We have been on holiday for two weeks.

senses: feel, hear, see, smell, taste, touch

Example: He has touched the painting.

brain work: believe, know, think, understand

Example: I have known him for 3 years.

Emphasis on completion or duration?

Do you want to emphasise the completion of an action or its continuous course (how has somebody spent his time)?

Present Perfect Simple	Present Perfect Progressive
Emphasis on completion I have done my homework. (Meaning: My homework is completed now.)	Emphasis on duration I have been doing my homework. (Meaning: That's how I have spent my time. It does not matter whether the homework is completed now.)

Result or side effect?

Do you want to express that a completed action led to a desired result or that the action had an unwanted side effect?

Present Perfect Simple	Present Perfect Progressive
desired result I have washed the car. (Result: The car is clean now.)	unwanted side effect Why are you so wet? - I have been washing the car. (side effect: I became wet when I was washing the car. It does not matter whether the car is clean now.)

Time + negation: last time or beginning of an action?

In negative sentences: Do you want to express how much time has past since the last time the action took place or since the beginning of the action?

Present Perfect Simple	Present Perfect Progressive
since the last time I haven't played that game for years. (Meaning: It's years ago that I last played that game.)	since the beginning I haven't been playing that game for an hour, only for 10 minutes. (Meaning: It's not even an hour ago that I started to play that game.)

Permanent or temporary?

If an action is still going on and we want to express that it is a permanent situation, we would usually use the Present Perfect Simple. For temporary situations, we would prefer the Present Perfect Progressive. This is not a rule, however, only a tendency.

Present Perfect Simple	Present Perfect Progressive
permanent James has lived in this town for 10 years. (Meaning: He is a permanent resident of this town.)	temporary James has been living here for a year. (Meaning: This situation is only temporary. Maybe he is an exchange student and only here for one or two years.)

Signal words

Present Perfect Simple	Present Perfect Progressive
how often ... times	how long since for

Exercises on Present Perfect Simple and Present Perfect Progressive

EXERCISE ONE

EXERCISE TWO

EXERCISE THREE

(INTERMEDIO 2) NB2.1 INGLÉS

lunes, 25 de abril de 2016

EXÁMENES DE MAYO

martes, 12 de abril de 2016

MUST, HAVE TO & SHOULD.

Modal Verbs of Obligation

lunes, 4 de abril de 2016

PRESENT PERFECT SIMPLE & CONTINUOUS