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