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 couldn't master you couldn't master he couldn't master we couldn't master you couldn't master they couldn't master	I couldn't be mastering you couldn't be mastering he couldn't be mastering we couldn't be mastering you couldn't be mastering they couldn't be mastering
Perfect	V-ing perfect
I couldn't have mastered you couldn't have mastered he couldn't have mastered we couldn't have mastered you couldn't have mastered they couldn't have mastered	I couldn't have been mastering you couldn't have been mastering he couldn't have been mastering we couldn't have been mastering you couldn't have been mastering they couldn't 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
couldn't I master? couldn't you master? couldn't he master? couldn't we master? couldn't you master? couldn't they master?	couldn't I be mastering? couldn't you be mastering? couldn't he be mastering? couldn't we be mastering? couldn't you be mastering? couldn't they be mastering?
Perfect	V-ing perfect
couldn't I have mastered? couldn't you have mastered? couldn't he have mastered? couldn't we have mastered? couldn't you have mastered? couldn't they have mastered?	couldn't I have been mastering? couldn't you have been mastering? couldn't he have been mastering? couldn't we have been mastering? couldn't you have been mastering? couldn't they have been mastering?