Can, Can't, Could, & Couldn't

1. Overview: Modal verbs "can," "can't," "could," and "couldn't" are used to express ability, possibility, and permission. They help us talk about what we are able to do or what we are not able to do. 2. Cases of Usage: Case 1: "Can" is used to express ability or skill. Example: I can swim. Case 2: "Can't" is used to express inability or something that is not possible. Example: She can't ride a bike. Case 3: "Could" is used to talk about past abilities or to make polite requests. Example: When I was younger, I could climb trees. Case 4: "Couldn't" is used to express past inability. Example: He couldn't play soccer last year. 3. Exceptions or Things to Pay Attention To: "Can" and "can't" are often used in everyday conversation. "Could" and "couldn't" are usually used when talking about the past or when making polite requests. Remember that "can" is for the present and "could" is for the past. 4. Additional Notes: Be careful with the contraction "can't"-it means "cannot." A common mistake is using "can" instead of "could" when talking about past abilities. Always use "could" for past situations.