Grammar Focus: Modals: Ability, Permission, Advice (can, could, should)

Modal verbs are auxiliaries followed by the base form of a verb.

• Ability: can (present) — I can come to your office. could (past ability or polite request) — I couldn't make it work. Could you spare some time?
• Permission: can (informal) / could (more polite) — Could I borrow your pen?
• Advice: should — I should have asked for help earlier. You should study harder.