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