Can you or not?
I would like to ask about the phrase: Can I use the Computer, car, pen, ....etc.
I would like to know if someone will ask you politely to give her the permission to use the Computer saying "Can I use the computer?" what you will understand of this?
My teacher used to say: "I don't know if you can use it, can you?"
It sounds to me like if he understand it as if she was questioning her appelities in using the computer!
By the way he is a British teacher, I am saying this in case you will say that the variety of English may make sense
Re: Can you or not?
It means that he was playing some practical jokes over us.
The variety of English has nothing to do with it.
"Can" is a modal which is used either to indicate Ability or to indicate Capability/Skill. It is ambiguous in the sense that one's Ability to do something might be compromised by
(i) a lack of knowledge or experience
(ii) the prevailing circumstances.
Thus, in isolation the question "Can Tom use the computer" could be taken to mean
(i) Does Tom have the knowledge and background that would confer upon him the capability or skill to use the computer
(ii) do present circumstances permit Tom the use of the computer. (eg. time; spare computers etc)
The question "Can I use a computer" would usually be taken to have meaning along the lines of (ii), because one would expect a person to know whether they themselves have or don't have a certain capability or skill.
The question "can you use a computer" could be easily taken to have either meaning, especially if the listener knows that the speaker has no prior knowledge as to the listener's abilities or skills. In fact in English one must occasionally seek clarification from a speaker because of this inherent linguistic ambiguity in English.
Your teacher should have made his jokes only after he had made you aware of this important linguistic point. My guess is that he was not aware of the idiosyncratic subtleties of Modality in English or of the importance that there is for teachers in finding ways to make learners aware of them. So yes, of course English speakers understand "Can you...?" questions, and they often can be confusing even for native speakers. Your teacher simply wasn't doing his job.
If you start your question with "May I..." "Could I...." Please can I...." and so on, not only is it more polite, it also immediately removes the ambiguity.
Thank you very much. This was useful. 8)