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