Estudiante

The verbs can, could, will, would, should, may, might, must, ought and shall are verbs which 'help' other verbs to express a meaning: it is important to realise that these"modal verbs" have no meaning by themselves. A modal verb such as would has several varying functions; it can be used, for example, to help verbs express ideas about thepast, the present and the future. It is therefore wrong to simply believe that "would is the past of will": it is many other things.

A few basic grammatical rules applyingto modal verbs

 Modal verbs are NEVER used with other auxiliary verbs such as do, does, did etc. The negative is formed simply by adding "not" after the verb; questionsare formed by inversion of the verb and subject.
 Modal verbs NEVER change form: you can never add an "-s" or "-ed", for example.
 Modal verbs are NEVER followed by to, withthe exception of ought to.

The modal auxiliary can is used
* to express ability (in the sense of being able to do something or knowing how to do something):
He canspeak Spanish but he can't write it very well.
* to expression permission (in the sense of being allowed or permitted to do something):
Can I talk to my friends in thelibrary waiting room? (Note that can is less formal than may. Also, some writers will object to the use of can in this context.)
* to express possibility:
Americanautomobile makers can make better cars if they think there's a profit in it.
Can has the same form for all the pronouns
What languages can you speak?   I can speak Spanish,Italian.
What sports can you play? I can play tennis and golf
Who can write in Japanese? I can
How fast can you run? I can run very fast!