I could master you could master she could master we could master you could master they could master
V-ing form
I could be mastering you could be mastering she could be mastering we could be mastering you could be mastering they could be mastering
Perfect
I could have mastered you could have mastered she could have mastered we could have mastered you could have mastered they could have mastered
V-ing perfect
I could have been mastering you could have been mastering she could have been mastering we could have been mastering you could have been mastering they could have been mastering
Negation
Simple form
I could not master you could not master she could not master we could not master you could not master they could not master
V-ing form
I could not be mastering you could not be mastering she could not be mastering we could not be mastering you could not be mastering they could not be mastering
Perfect
I could not have mastered you could not have mastered she could not have mastered we could not have mastered you could not have mastered they could not have mastered
V-ing perfect
I could not have been mastering you could not have been mastering she could not have been mastering we could not have been mastering you could not have been mastering they could not have been mastering
Interrogative form
Simple form
could I master? could you master? could she master? could we master? could you master? could they master?
V-ing form
could I be mastering? could you be mastering? could she be mastering? could we be mastering? could you be mastering? could they be mastering?
Perfect
could I have mastered? could you have mastered? could she have mastered? could we have mastered? could you have mastered? could they have mastered?
V-ing perfect
could I have been mastering? could you have been mastering? could she have been mastering? could we have been mastering? could you have been mastering? could they have been mastering?
Interro-negative form
Simple form
could I not master? could you not master? could she not master? could we not master? could you not master? could they not master?
V-ing form
could I not be mastering? could you not be mastering? could she not be mastering? could we not be mastering? could you not be mastering? could they not be mastering?
Perfect
could I not have mastered? could you not have mastered? could she not have mastered? could we not have mastered? could you not have mastered? could they not have mastered?
V-ing perfect
could I not have been mastering? could you not have been mastering? could she not have been mastering? could we not have been mastering? could you not have been mastering? could they not have been mastering?