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