The plural form of could is coulds.

What is the plural for could?

Noun. could (plural coulds)

Can or could use?

Can, like could and would, is used to ask a polite question, but can is only used to ask permission to do or say something ("Can I borrow your car?" "Can I get you something to drink?"). Could is the past tense of can, but it also has uses apart from that--and that is where the confusion lies.