Could is a helping verb that shows possibility, ability, or permission in a softer way than “can.”

When you say “I could go to the park,” you mean it's possible but not certain. When your teacher says “You could finish this by tomorrow,” she means you have the ability to do it. When your mom says “You could have one more cookie,” she's giving permission in a gentle way.

Could often appears when we're being polite or making suggestions. “Could you please pass the salt?” sounds more courteous than “Can you pass the salt?” When your friend asks “Could we play soccer instead?” she's proposing an idea without demanding it.

The word also talks about past abilities: “When I was younger, I could climb that tree easily” means you had that ability before, even if you don't anymore. Similarly, “I could have won the race” suggests a missed possibility, something that was achievable but didn't happen.

Notice how could makes statements less forceful. “You should study” sounds like an order, while “You could study now” sounds like a suggestion. This softer quality makes could useful when you want to be thoughtful about how others hear your words.