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