1. Here you have a little introduction
to know about the topic. Read it
with your teacher and then talk with
a classmate about it.

2. The modal verb CAN is used to speak about
abilities in the present. The negative for is can
not or on its contractive form can´t and it is
used to express lack of ability.

3. For instance:
•I can swim.
•I can dance very well.
•Can you jump over the desk? Yes, I can/ No I can´t.
NOTE: Can not or can´t are denoting that the person is not capable to
jump over the desk in the present.

4. When you talk about abilities in the present, it
is also used the expression be able to.
For example:
•I am able to run very fast.
•She is not able to cook delicious meal
NOTE: can is much commonly used, be able to is more formal and it
is not so used in written informal English.

5. When we want to speak about abilities in the past
we can use the past form of can, the modal verb
could/could not (its contractive form couldn´t).
For example:
•When I was young, I could run 10 km a day.
•She couldn´t ride by horse when she was six
years old. (now, she can ride by horse)
•That day I couldn´t do my homework.
NOTE: could not/couldn´t are used to express lack of ability to do
something in the past.

6. Furthermore, if you want to express an ability in a
particular event in the past, you can use was/were
able to.
For instance:
•Even though, she was eighty five years old, she
was able to fly an aeroplane.
•They were able to climb a mountain when they
were twenty years old. (now, they can not do it)

7. But, when we form sentences in the past using
verbs of sense perception(see, smell, taste,
hear, feel), and verbs of thinking (understand,
decide, remember, believe, guess), we must use
could/couldn´t. We can not use was/were able
to.
For instance
There were something burning at that house
because I could smell it.
NOT: There were something burning at that
house because I was able to smell it.

8. When I was at school sitting near the window, I
could see the stranger man.
NOT: When I was at school sitting near the
window, I was able to see the stranger man.
They said, they couldn´t believe their eyes.
NOT: They said, they weren´t able to believe their
eyes.