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