Verb tense confusion - how can "could" be used to describe future events?

[pizzadude]

Hi.

I am having confusions with verb tense. If "could" is the past tense of "can", then how can "could" be used in a sentence to describe a future event like the following:

I could fail math class next week.

The word "should" (which is the past tense of shall) can also be used to describe future events like the following:

If you should ever find yourself in such a situation...

The second question I have is if I am in a room with a friend and I ask that friend to pass a pencil to me by saying, "Billy, could you pass that pencil to me". Is that sentence correct? I use "could" instead of "can" to describe an event in the present or future instead of in the past. I hear people say it like that all the times, and I don't know if it's correct or not.

[David L.]

can (could) and shall (should) are modal verbs and go together with another verb to indicate the tense
"I could fail math class next week."
I could have failed the math exam last week without all the tutoring you gave me."

"should' : you need to review in your dictionary all the uses of this word quite apart from that as past tense of 'shall'

'could' : Again, you will find these uses described in your dictionary.

[Soup]

Hi pizzadude

This is in addition to David's help.

Because could expresses a possibility, it can be used to express present, past, and future:

Present: Could you pass me a pencil?
=> a polite request
Note that, speakers will also use can.

Past: I couldn't call you yesterday.
=> meaning, I wasn't able to.

Future: I could call you tomorrow.
=> meaning, there is a possibility if (a) you so wish it or (b) I so wish it.


"Billy, could you pass that pencil to me?"
"Billy, can you pass that pencil to me?"