The modal verbs are:

can could
may might
shall should
will would
must  

We use modal verbs to show if we believe something is certain, probable or possible (or not). We also use modals to do things like talking about ability, asking permission making requests and offers, and so on.
 

Section: 

Comments

Dear Sir,

Why do we use the structure "If I were" to show imagination?

"if I were" shows past form of tense.

Kindly guide.

Hello amol,

The past simple is used to speak about unreal or imaginary situations. So if you say 'if I were a rich man', it means you are not a rich man - you are talking about an imaginary situation.

See the section on the second conditional on our Conditionals 1 page - I think this will help you see how this works.

All the best,
Kirk
The LearnEnglish Team

i can (simple present, CAN is main verb)

i can a can

i can cans

a can can be canned

Could a can have been canned?

canned cans can can cans (personification)

can canned can can cans?

sir, i know these sentences are not used normally,
but i tried to make sentences
is there any grammatical mistake?

One woman is able to destroy the whole world.
One woman is capable of destroying the whole world.

.
can 'BE ABLE TO' be replaced with CAPABLE OF?

Hello pyramid,

Yes, you can do that and in general they mean the same thing.

All the best,
Kirk
The LearnEnglish Team

Hello Sir,

If "COULD" is the past form of "CAN", why can we use it to make polite requests in present tense?

Hello amol,

'could', like almost any auxiliary verb, is used in many, many different ways. Its use in polite requests is one use and its use as a past form of 'can' is another. 

All the best,
Kirk
The LearnEnglish Team

sir,
1) when we use COULD to make a request, is it considered to be in simple present tense.
commands, requests are always in simple present.
.
2) can other tenses or special patterns be used for making command?

.
.
eg.
1) someone is sitting in the chair,
i saw him/her and said, " i want to sit here.

.
2) hadn't you sat in the chair, it would have been fine?

are above sentences considered to be commands?

Hello pyramid.org,

'Could' is a modal verb and it is not appropriate to describe it with names given to non-modal verb forms. There are many forms used to give instructions or commands. However, we cannot provide lists such as this in the comments sections. We're happy to provide answers to concrete questions, of course.

Your first example is grammatically correct but is rather rude. We would not simply say 'I want to sit here', but would preface it with 'Excuse me...' or 'I'm sorry but...' Of course, the tone of voice is key too.

Your second sentence is not grammatically correct and I think it sounds more like criticism than any kind of instruction.

 

Best wishes,

Peter

The LearnEnglish Team

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