Can And Could

The modal auxiliary Can is used

* To express ability ( in the sense of being able to do something or knowing how to do something) Example: He can speak Spanish but he can’t write it very well.* To expression permission (in the sense of being allowed or permitted to do something)Example: Can I talk to my friends in the library waiting room?
* To express theoretical possibility:American automobile makers can make better cars if they think there’s a profit in it.

Can has the same form for all the pronouns.
I/ you/he/she/it/we/they CAN

Positive sentences |Negative sentences use can + not (can’t) | Interrogative forms | Examples of wh questions with Can |
1.- You can play basketball. | 1.- The baby can’t eat on his awn. | 1.- Can you solve this addition? |1.- What languages can you speak? |
2.- He can fly! Well, he is Superman. | 2.- We can’t speak Japanese. | 2.- Can we play like them? | 2.- Who can write in japanese? |
3.- We can ride a bicycle.| 3.- I can’t water ski. | 3.- Can he program a Computer? | 3.- How fast can you run? |

The modal auxiliary could is used.

* To express an ability in the past. Example: I could always beatyou at tennis when we were kids.
* To express past or future permission. Example: Could I bury my cat in your back yard?
* To express present possibility. Example: We could always spend theafternoon just sitting around talking.
* To express possibility or ability in contingent circumstances. Example: If he studied harder, he could pass this course.
I/ you/he/she/it/we/theyCOULD

Positive sentences | Negative sentences | Interrogative sentences | Examples of wh questions with Could |
1.- He could speak English very well 3 years ago. | 1.- It couldn’t snow tomorrow. |1.-Could he do his work so well as she did it? | 1.-When Could you come? |
2.- You could see the doctor. | 2.- She couldn’t write it. | 2.- Could you help me? | 2.-who Could you call James? |...