Grammar - Pre-Intermediate
'For', 'Since' and 'Ago'.
We can use for or since with the present perfect to say how long something has happened.
I have known him since 1980.
The meaning is the same. For is used to talk about a period of time, since to talk about when the action started.
ago is more often used with the past simple to say when something started.
He started his own business six months ago.
So the difference between 'since' and 'ago'?
Since tells us the starting point of an action which is still continuing now. Ago tells us the starting point of an action which is finished.
I have lived in this city since 1980.
Modal verbs are irregular auxiliary verbs (they don't have regular past and present forms, for example) that express ability, necessity, requests, advice, permission, probability and so on. They are generally used with other verbs in the infinitive:
(See the next sections for modal verbs "will" and "must/mustn't".)
I must go to the hotel tomorrow.
There are modal verbs which have different meanings and different functions.
Should / Shouldn't
This is used to give advice or to express what you expect.
You should go to the doctor if your headaches continue.
We use "shouldn't" to talk about something you are advising a person not to do.
If you want to pass your exams, you shouldn't go out tonight.
May / Might
These are similar in meaning and are used to express possibility.
Q: Are you going to the cinema tonight?
Used in questions, these two are ways of asking for something in a polite/formal way.
Might I borrow your telephone for a few moments?
Can / CouldWe have already seen that "can" can be used to talk about ability, with "could" used in the past:
I can see, but I can't dance.
We can also use "can" to talk about possibility, permission and make polite requests:
I can't come to the party tonight. (possibility)
Note that all three of these modal verbs are followed directly by an infinitive verb without "to".
'Will' or 'Going To'
We have already discussed the use of "going to" to talk about the future. It is used to talk about plans already made and also to make predictions based on evidence we see now.
We will now talk about "will" and then see how they differ in direct comparison.
Will is a modal verb and is followed directly by an infinitive verb without "to".
I will see you tomorrow.
The main functions of "will" are:
a. to predict a future event:
The party will be at my house at eight o'clock.
b. to express a spontaneous decision:
I'll answer the phone.
Note the difference between will and going to in this use. We use going to if a decision has been made before speaking, but will if the decision is made now.
John: What are you doing this weekend?
In this dialogue, Mary's first answer uses going to as it is a plan she made before. Her second answer uses will as she now has to make a new plan, and her plan to visit Stefano is made now, as she speaks.
c. to express a prediction based on opinion, not on fact.
Howes will win the election.
Here, expressions of opinion and belief are common:
d. The old form of will, "shall" is often used to make offers and suggestions.
Shall we leave now? It's late.
"Have To" and "Must"
These two are very similar and both are used to talk about obligation.
Used in the positive/affirmative, these two are almost identical. They are used to say that there is an obligation, necessity for someone to do something.
Drivers in England have to drive on the left of the road.
Usually, have to is used when there is an external obligation on you, must when the obligation comes from the speaker.
Note the difference:
It's late, I'm really tired, I must go now. Bye!
Note the construction:
Used in the negative, have to and must are very different.
You mustn't drive over 70mph in this area.
Don't have to, on the other hand, means there is no obligation for you to do something. In other words, it isn't necessary.
Rich people don't have to work.
Must doesn't have a past form so you should use had to.
We missed the last bus last night so we had to catch a taxi.
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