Auxiliary verbs (can and could)

Auxiliary verbs which can also be called modal verbs. In English we know a lot of modal verbs, for example: cans, must, have to, has to, may etc. Now we focus on the modal verb can and can.

Can be used for:
* Express ability
Example:
^I can swim.
^I can swim. He can speak English
^He can speak English. Ron can drive     a car.
^Roni can drive a car.

* Used to make sentence requests / requests
We usually use question sentences if we want to ask someone to do something.
Example:
^Can you turn on the TV?
^Can you help me?
^Can you be quiet!

* Permission
We usually use cans to request or give permission.
Example:
A: Can I smoke in this room?
B: You can't smoke here.

For more details, note the formula for using cans below:

Positive Sentence
S + can + V1
Example:
^She can play soccer.
^They can swim.

Negative sentence
S + cannot / can't + V1
example:
^She can't play soccer.
^They can't swim.

Interrogative sentence
Can + S + V1
example:
^Can you sing a song? Yes, I can / No, I can't
^Can she play soccer? Yes, She can / No, She can't
^Can they swim? Yes, They can / No, They can't

Could be used for:
* Past / past shapes of cans, can be used to explain abilities in the past.
Example:
^I could swim when I was 5 years old. ^Toni could speak 7 languages.

To change the sentences into negative sentences, just add "notes" after the can.

^I could not swim when I was 5 years old.
^Toni Couldn't speak 7 languages.

* To make a sentence request / request and also an order / order
In this case if we use could in a command sentence or request, it will look formal or more polite when compared to using a can.
Example:
^Could you help me, please?
^Could you turn on the Tv, please? ^Could you tell me where the hospital is, please?