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