could
1 used as the past tense of ‘can’
2 used ask if you can do sth
3 used to politely ask an to do sth for you
4 used to show that sth is or might be possible
5 used to suggest sth
6 used to show that you are annoyed that an did not do sth
7 (informal) used to emphasize how strongly you want to express your feelings
couldの意味はこの7つのみです。
おそらく1番の意味で使えると思っているのでしょうがこれは時制の一致のときの話ですので本文ではそういう意味を持ちません。(否定文はただのcanの過去の意味を持てる)
