'Can' expresses present ability, while 'could' indicates past ability. The document provides examples of affirmative, negative, and interrogative forms of both 'can' and 'could', along with common mistakes to avoid. Exercises are included to practice the correct usage of these modal verbs.

1. CAN AND COULD
FOR ABILITY
Prof. Jeraldin Ballesteros M.

2. UNDERS
TANDIN
G "CAN"
• "Can" is used to express present
ability. It shows what someone
is able to do now or generally.
• Examples:
• I can play the guitar.
• She can speak three languages.
• They can run 10 kilometers.
• We can solve this problem.

3. UNDERSTANDING "COULD"
• "Could" is used to express past ability. It shows what someone
was able to do in the past but possibly can’t do anymore.
• Examples:
• When I was younger, I could climb trees.
• He could swim very fast when he was a teenager.
• We could travel often before the pandemic.
• They could dance for hours when they were kids.

4. Affirmative
form of "can"
Use "can" to describe
something you are able to do
now.

5. Affirmative form of
"can"
• Examples:
• I can play the piano.
• We can meet tomorrow.
• They can read in English.
• She can cook Italian food.

6. NEGATIVE FORM
OF "CAN"
• Use the negative form to
describe what you are not
able to do now.

7. NEGative form of
"can"
Examples:
• I can’t drive a car.
• She can’t sing very well.
• We can’t attend the meeting today.
• They can’t understand Russian.

8. INTERROGATIVE FORM OF "CAN"
Use "can" in questions to ask about present abilities.

9. INTERROGATIVE
FORM OF "CAN"
Examples:
• Can you cook?
• Can she play the violin?
• Can they run fast?
• Can we finish this by tomorrow?

10. COULD

11. AFFIRMATIVE FORM OF
"COULD"
• Used to describe what you were able to do in the past.
Subject + could + base for the verb + compl.
She could swim when she was 5.

12. AFFIRMATIVE
FORM OF "COULD"
Examples:
• I could read when I was five.
• She could play chess as a child.
• We could go anywhere when we had
a car.
• He could lift heavy weights when he
was younger.

13. negATIVE FORM OF "COULD"
• Used to describe what you were not able to do in the past.
Subject + could not (couldn't) + base for the verb + compl.
She couldn't swim when she was
5.

14. negATIVE FORM
OF "COULD"
Examples:
• I couldn’t swim when I was a child.
• He couldn’t understand French
back then.
• They couldn’t afford a car last year.
• She couldn’t read until she was six.

15. INTERROGATIVE FORM OF
"COULD"
• Use "could" in questions to ask about past abilities.
Could + subject + base for the verb + compl.
Could she swim when she was 5?
Yes, she could
No, she couldn't

16. Interrogative
form of "could"
Examples:
• Could you swim when you were
younger?
• Could she play the piano as a child?
• Could they speak French when they lived
in Paris?
• Could you run fast when you were in
school?

17. COMMON MISTAKES WITH
"CAN" AND "COULD"
Avoiding Common Errors:
• Mistake 1: Using the wrong form.
• Incorrect: I could swim now.
• Correct: I can swim now.
• Mistake 2: Double negatives.
• Incorrect: I couldn’t never do that.
• Correct: I couldn’t do that.
• Mistake 3: Using "could" for present abilities.
• Incorrect: He could drive.
• Correct: He can drive.

18. Exercise 1
• Instructions: Fill in the sentences using "can" or "could"
depending on the context.
• When I was younger, I _______ run 10 kilometers easily.
• She _______ cook very well now.
• They _______ speak French fluently when they lived in France.
• He _______ play the guitar, but now he has forgotten how.

19. Exercise 2
Instructions: Create questions using "can" or "could" for the
following situations:
Ask your friend if they can play an instrument.
Ask someone if they could ride a bike when they were younger.
Ask if your classmate can help you with your homework.
Ask your parents if they could travel often when they were
young.

20. Thank you!
Are there any questions?