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