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