"would", "will","could", "can" are called Modal Auxiliary Verb. It is necessary to use auxiliary verbs in the formation of both questions and negatives. eg: Can she speak English? Will you come to my house today? Would you carry this for me? I wonder if he could get cheap air fares I can write very well. The meaning of this auxiliaries :- "will" (past Would) - prediction (eg: She will have arrived in Japan by now) - willingness (eg: She will help you with your bags.) - request (eg: Will you take this for me?) (eg: Would you clean this cups for me?) - invitation (eg: Will you be free to come to my house tonight?) (eg: Would you like to play with me?) - offer (eg: Would you like another glass of water?) "can" (past Could) -ability (eg: I can run very fast) - sometimes (The electrical can be dangerous) - requesting permission (eg: Can I borrow your pen?) -sugesstion (eg: You could peel those apples for me)

Hmmmmm - you shouldn't but you will hear it. Can shows certainty (or ability in the present/future) Could shows possibility (or ability in the past) Could is also politer than can when asking permission for something It is much the same for will and would (although we do not use these to indicate ability - that is the role of can/could!) For example; Please can you come here? Yes I can / No I can't Will you come here please? Yes I will / No I won't Would you go there? Yes I would / No I wouldn't Could you come here? Yes I could / No I couldn't (ps it should always be come here or go there not another combination of the words :))