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