Modal verbs/can – could and should

"Can," "could," and "should" are modal verbs in English, each with distinct uses.

can

"I can swim." (present ability)

"It can rain later." (present possibility, often with a higher probability)

"Can I borrow your pen?" (permission, informal)

could

"I could play the piano when I was younger." (past ability)

"It could rain later." (past possibility, often with a lower probability)

"Could you please give me your pen?" (polite request)

should

"You should eat more vegetables." (recommendation/advice) "I should be home by 10 pm." (obligation/expectation) "The train should arrive soon." (probability)

In essence, "can" is the most straightforward, "could" adds a layer of past tense or politeness, and "should" introduces advice, obligation, or expectation.