talk about a skill or possibility in
the present, or to ask permission
Example
I can call you later.
John can speak French.
Could
talk about a skill or possibility in the
past or future, or to ask for something
politely
Example
I could help you if you want.
Grandpa could run very fast as a young man.
May
talk about a possibility in the future or the
present, or to ask for something politely
Example
Tal vez llegue tarde.
Can we come in?
Shall
hablar de algo que se hará en
el futuro
Example
I'm not going to give up!
Do I put the water to heat?
Must
talk about an obligation, a ban or a need
Example
I have to go!
He has to be crazy.
Should
talk about an obligation or recommendation
Example
Everyone must arrive on time.
You should try this pie
Would
talk about a preference or custom in the
past, or to ask something politely
Example
I would like to go to the cinema.
Grandma went to work by
bike when she was young.
Will
talk about something that will be done in the future
Example
I will see you later.
Will you be here tomorrow?
Rules
They are always followed by an infinitive verb, since they have
no meaning for themselves. Normally this verb does not lead to,
although there are some exceptions that are also considered
modal verbs: be able to, need to, have to and ought to.
In interrogative and
negative forms, they
do not need to add the
auxiliary (do or does).
For example: Can you
come with me
tomorrow?
They do not conjugate, that is,
they do not add -s in the third
person singular and have no
past or future. Nor do they
have infinitive, compound or
progressive times.