Can is pronounced both strongly as "can" and weakly as "c'n". Strong form is used in short answers and when emphasizing the word. Can is longer and higher in pitch than "c'n"
Both can and could are used in present tense. They always require a verb stem after them. They cannot be followed by 'to'. They can replace other auxiliary verbs
Can and could are modal verbs expressing possibility or ability. Modal verbs include will/would, shall/should, may/might, must, ought to
Both express abilities, knowledge, or talent. Can is used for present and future. Both can be used for negation with "cannot" or "not able to"
Used for present abilities and general possibilities. Can't/cannot used for negation. Can be used informally for offers and requests
May appeared in manuscripts from 8th century as strength/power verb. May evolved to mean ability, possibility, and permission before 1000AD. Can emerged around 1000 as "know" and "have ability". By 1800s, can also meant permission