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