I could quit you could quit he could quit we could quit you could quit they could quit
V-ing form
I could be quitting you could be quitting he could be quitting we could be quitting you could be quitting they could be quitting
Perfect
I could have quit you could have quit he 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 he could have been quitting we could have been quitting you could have been quitting they could have been quitting
Negation
Simple form
I couldn't quit you couldn't quit he couldn't quit we couldn't quit you couldn't quit they couldn't quit
V-ing form
I couldn't be quitting you couldn't be quitting he couldn't be quitting we couldn't be quitting you couldn't be quitting they couldn't be quitting
Perfect
I couldn't have quit you couldn't have quit he couldn't have quit we couldn't have quit you couldn't have quit they couldn't have quit
V-ing perfect
I couldn't have been quitting you couldn't have been quitting he couldn't have been quitting we couldn't have been quitting you couldn't have been quitting they couldn't have been quitting
Interrogative form
Simple form
could I quit? could you quit? could he quit? could we quit? could you quit? could they quit?
V-ing form
could I be quitting? could you be quitting? could he be quitting? could we be quitting? could you be quitting? could they be quitting?
Perfect
could I have quit? could you have quit? could he 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 he have been quitting? could we have been quitting? could you have been quitting? could they have been quitting?
Interro-negative form
Simple form
couldn't I quit? couldn't you quit? couldn't he quit? couldn't we quit? couldn't you quit? couldn't they quit?
V-ing form
couldn't I be quitting? couldn't you be quitting? couldn't he be quitting? couldn't we be quitting? couldn't you be quitting? couldn't they be quitting?
Perfect
couldn't I have quit? couldn't you have quit? couldn't he have quit? couldn't we have quit? couldn't you have quit? couldn't they have quit?
V-ing perfect
couldn't I have been quitting? couldn't you have been quitting? couldn't he have been quitting? couldn't we have been quitting? couldn't you have been quitting? couldn't they have been quitting?