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