Cambridge Grammar of English Hardback with cd-rom a comprehensive Guide

Good wishes and curses

May

is used in formal expressions of good wishes and in formal curses:

[speech at a wedding, addressing the newly-married couple]

May you both have a long and happy married life together.

May you rot in hell!

Û

also 385 Might; 384 Can, could and may; 386 Could, may and might

Û

408–423 Speech acts

CAN, COULD AND MAY

384

Probability

When assessing probabilities, can refers to what the speaker believes to be a fact

or to be usually the case. Could and may refer to possible events. Compare:

It 

can be very cold in Stockholm, so take a big coat.

(this is a known fact)

It 

could/may be very cold in Stockholm, so take a big coat.

(it is possible that it will be cold in Stockholm when you are there)

Could

and may rather than can are used to speculate about whether something is

true or possible:

A: Where’s Julia?

B: She could be in the garden.

(or: She may be in the garden.) 

(She can be in the garden.)

It 

could rain this afternoon.

(It can rain this afternoon.)