Can or could?

[Weibing]

Hi guys, I decided to break the silence with a new thread. My query seems so simple or too general?! I know 'could' is the past form of 'can'. In addition to this obvious,basic distinction, can/could you give me some more suggestions on how to use 'could' properly? Thanks!

[Kevin Vosper]

Dear Weibing

You are right in that we do use "could" when talking about past abilities eg:

"When I was a teenager I could walk twenty kilometers."

or

"Early man could use fire."

However the relationship between "could" and "can" is in fact a little more complex than just past and present. Compare the following:

"Could you pass the salt?"

"Can you pass the salt?"

It is possible to use both sentences in exactly the same situation, ie a dinner party. Here there is no question about "could" being about past time but the relationship between the two words is in fact exactly the same. I would use "can" to a close friend and "could" to a more distant person such as my boss. The key word is "distance." Here it refers to distance in a relationship but in the previous example it refered to distance in time eg the past.

"Could" is also used in conditional sentences and again is used as a more "distant" variation of "can." In this case when we want to show distance between something which is probable and something which is improbable. For example:

"If I accept the job I can buy a new car." (probable)

"If I won the lottary I could buy a new car." (improbable)

Notice also that "win" changes to "won" in conditionals. The past simple is also used in English to show distance in the same way.

The same relationship also exists between other modal pairs eg:

will-would
shall-should
may-might

For some reason "must" does not have a partner. If anybody knows why please post the answer since I would love to know.

I find it easiest when teaching to teach the idea of distance in modals right from the start because students who just think "could" is a past form of "can" get very confused when they find out this isn't always true.

Sorry I haven't been posting over the last few months but I've been without a computer.

Best wishes

Kevin

[Weibing]

Hi, Kevin, long time no see! Welcome back and thank you very much for your perfect answer! I'm glad you came back here again - I really like to enjoy your posts (informative but readable). Actually, I (maybe not only I) was hoping you would appear and continue to post - a dream come true now!

As for my query, you answered it with the key word 'distance' - distance in time, distance in a relationship. Yes, it's quite understandable. And I'd like to add one more 'distance' - 'distance' in the extent of politeness and certainty.

Thanks again!

Best wishes

Weibing