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