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