UppInt A: COULD Explanation

An extension of what we briefly discussed in class today...

COULD/COULDN'T

(+) = affirmative  (-) = negative   (1) = specific one time ability  (+1) = general past ability

  -use COULD (+) /COULDN'T (-) to express ability in the past
 - was able to = could

When I was young, I could play tennis very well. (+) (+1)

(When I was young, I was able to play tennis very well.) (+)(+1)

She could read when she was four. (+)(+1)

(She was able to read when she was four.) (+)(+1)

*COULD is not used when we want to say somebody did something one time (expressing a fulfilled ability (+) on one particular occasion (1)). Instead, we use: was/were able to, manage to (implied difficulty), succeed in (implied difficulty/more formal)

    How many slices of pizza could you eat?

Instead use: How many slices of pizzas were you able to eat? (+)(1)

 OR      How many slices of pizza did you manage to eat?  (+)(1)

             OR     How many slices of pizza did you succeed in eating?   (+)(1)

**But, we can use the negative couldn’t to say that something did not happen (-) on one occasion (1)

            I couldn’t go to the concert yesterday because I was busy. (-) (1)

            He couldn’t find her house.   (-) (1)

***Exception to this rule: with verbs of perception/senses and thinking, we can use COULD for (+) and (1)
 
OK                I could smell burning  (+) (1)
OK                We could understand her feelings.  (+) (1)


In conclusion, before you use COULD, think about.. is the sentence affirmative/positive (+) and is the sentence about a specific one time event (1)? If the answer is YES to both of these factors then you can't use COULD

USES OF COULD EXPLANATION + EXERCISES
http://www.englishpage.com/modals/could.html