Modal verbs - Can and Could - English Grammar lesson :
In this lesson Rachna explains the difference between 'could' and 'can' when expressing possibility? Most of the time it is clear from the context, but use of can can also express possibility (rather than ability). For example, giving advice answering the question:
How can/could I improve my English?
You can/could listen to the radio, watch TV and read the newspaper.
Both are possible. Students want to know when to use 'could' and when to use 'can'.
Similarly, How could I improve my English? is more a request for advice, whereas How can I improve my English?is more a factual question about available options. (But of course we can also answer this question by giving advice.)
Can and could, like the other modal verbs, have developed quite a range of meanings and uses. You ask how to explain the difference, and explanation can certainly help, but learning all the ins and outs of these verbs is a long process which requires plenty of experience, observation and experiment. Watch this video lesson to understand when to use Can and Could.