I could screen you could screen he could screen we could screen you could screen they could screen
V-ing form
I could be screening you could be screening he could be screening we could be screening you could be screening they could be screening
Perfect
I could have screened you could have screened he could have screened we could have screened you could have screened they could have screened
V-ing perfect
I could have been screening you could have been screening he could have been screening we could have been screening you could have been screening they could have been screening
Negation
Simple form
I could not screen you could not screen he could not screen we could not screen you could not screen they could not screen
V-ing form
I could not be screening you could not be screening he could not be screening we could not be screening you could not be screening they could not be screening
Perfect
I could not have screened you could not have screened he could not have screened we could not have screened you could not have screened they could not have screened
V-ing perfect
I could not have been screening you could not have been screening he could not have been screening we could not have been screening you could not have been screening they could not have been screening
Interrogative form
Simple form
could I screen? could you screen? could he screen? could we screen? could you screen? could they screen?
V-ing form
could I be screening? could you be screening? could he be screening? could we be screening? could you be screening? could they be screening?
Perfect
could I have screened? could you have screened? could he have screened? could we have screened? could you have screened? could they have screened?
V-ing perfect
could I have been screening? could you have been screening? could he have been screening? could we have been screening? could you have been screening? could they have been screening?
Interro-negative form
Simple form
could I not screen? could you not screen? could he not screen? could we not screen? could you not screen? could they not screen?
V-ing form
could I not be screening? could you not be screening? could he not be screening? could we not be screening? could you not be screening? could they not be screening?
Perfect
could I not have screened? could you not have screened? could he not have screened? could we not have screened? could you not have screened? could they not have screened?
V-ing perfect
could I not have been screening? could you not have been screening? could he not have been screening? could we not have been screening? could you not have been screening? could they not have been screening?