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