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