I could surf you could surf she could surf we could surf you could surf they could surf
V-ing form
I could be surfing you could be surfing she could be surfing we could be surfing you could be surfing they could be surfing
Perfect
I could have surfed you could have surfed she could have surfed we could have surfed you could have surfed they could have surfed
V-ing perfect
I could have been surfing you could have been surfing she could have been surfing we could have been surfing you could have been surfing they could have been surfing
Negation
Simple form
I could not surf you could not surf she could not surf we could not surf you could not surf they could not surf
V-ing form
I could not be surfing you could not be surfing she could not be surfing we could not be surfing you could not be surfing they could not be surfing
Perfect
I could not have surfed you could not have surfed she could not have surfed we could not have surfed you could not have surfed they could not have surfed
V-ing perfect
I could not have been surfing you could not have been surfing she could not have been surfing we could not have been surfing you could not have been surfing they could not have been surfing
Interrogative form
Simple form
could I surf? could you surf? could she surf? could we surf? could you surf? could they surf?
V-ing form
could I be surfing? could you be surfing? could she be surfing? could we be surfing? could you be surfing? could they be surfing?
Perfect
could I have surfed? could you have surfed? could she have surfed? could we have surfed? could you have surfed? could they have surfed?
V-ing perfect
could I have been surfing? could you have been surfing? could she have been surfing? could we have been surfing? could you have been surfing? could they have been surfing?
Interro-negative form
Simple form
could I not surf? could you not surf? could she not surf? could we not surf? could you not surf? could they not surf?
V-ing form
could I not be surfing? could you not be surfing? could she not be surfing? could we not be surfing? could you not be surfing? could they not be surfing?
Perfect
could I not have surfed? could you not have surfed? could she not have surfed? could we not have surfed? could you not have surfed? could they not have surfed?
V-ing perfect
could I not have been surfing? could you not have been surfing? could she not have been surfing? could we not have been surfing? could you not have been surfing? could they not have been surfing?