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