Compare and contrast the modal auxiliary verbs ... - SS1 English Vowels, vocabulary, comprehension and model auxiliary verb Question

The modal auxiliary verbs can and could are often confused, but they have different meanings. Can is used to express ability or permission, while could is used to express past ability or permission. 

For example, the sentence "I can swim" expresses the ability of the speaker to swim. The sentence "You could go to the park" expresses the permission of the listener to go to the park.

In the past tense, can becomes could. For example, the sentence "I could swim when I was younger" expresses the past ability of the speaker to swim.

The modal auxiliary verb could can also be used to express a hypothetical situation. For example, the sentence "If I could fly, I would travel the world" expresses the speaker's desire to travel the world if they could fly.