English verb conjugation
COULD MASTER

Regular verb: master - mastered - mastered

Affirmation

Simple form	V-ing form
I could master you could master he could master we could master you could master they could master	I could be mastering you could be mastering he could be mastering we could be mastering you could be mastering they could be mastering
Perfect	V-ing perfect
I could have mastered you could have mastered he could have mastered we could have mastered you could have mastered they could have mastered	I could have been mastering you could have been mastering he could have been mastering we could have been mastering you could have been mastering they could have been mastering

Negation

Simple form	V-ing form
I could not master you could not master he could not master we could not master you could not master they could not master	I could not be mastering you could not be mastering he could not be mastering we could not be mastering you could not be mastering they could not be mastering
Perfect	V-ing perfect
I could not have mastered you could not have mastered he could not have mastered we could not have mastered you could not have mastered they could not have mastered	I could not have been mastering you could not have been mastering he 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	V-ing form
could I master? could you master? could he master? could we master? could you master? could they master?	could I be mastering? could you be mastering? could he be mastering? could we be mastering? could you be mastering? could they be mastering?
Perfect	V-ing perfect
could I have mastered? could you have mastered? could he have mastered? could we have mastered? could you have mastered? could they have mastered?	could I have been mastering? could you have been mastering? could he have been mastering? could we have been mastering? could you have been mastering? could they have been mastering?

Interro-negative form

Simple form	V-ing form
could I not master? could you not master? could he not master? could we not master? could you not master? could they not master?	could I not be mastering? could you not be mastering? could he not be mastering? could we not be mastering? could you not be mastering? could they not be mastering?
Perfect	V-ing perfect
could I not have mastered? could you not have mastered? could he not have mastered? could we not have mastered? could you not have mastered? could they not have mastered?	could I not have been mastering? could you not have been mastering? could he not have been mastering? could we not have been mastering? could you not have been mastering? could they not have been mastering?