I could diagram you could diagram she could diagram we could diagram you could diagram they could diagram
V-ing form
I could be diagraming you could be diagraming she could be diagraming we could be diagraming you could be diagraming they could be diagraming
Perfect
I could have diagramed you could have diagramed she 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 she 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 she 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 she 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 she 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 she 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 she diagram? could we diagram? could you diagram? could they diagram?
V-ing form
could I be diagraming? could you be diagraming? could she be diagraming? could we be diagraming? could you be diagraming? could they be diagraming?
Perfect
could I have diagramed? could you have diagramed? could she 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 she 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 she 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 she 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 she 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 she have been diagraming? couldn't we have been diagraming? couldn't you have been diagraming? couldn't they have been diagraming?