Can and Could: Modals of Ability
A modal verb is a type of auxiliary (helping) verb that has no meaning on its own but it modifies the main verb, changes its meaning and gives more details about the action. Could is the past form of the modal verb can. These are types of modal auxiliary verbs used to express the idea of ability or permission {see Can: Modals of Ability, A1 Level}. https://open.books4languages.com/english-a2-grammar/chapter/can-and-could-modals-of-ability/