English verb conjugation
COULD ALTER

Regular verb: alter - altered - altered

Affirmation

Simple form	V-ing form
I could alter you could alter he could alter we could alter you could alter they could alter	I could be altering you could be altering he could be altering we could be altering you could be altering they could be altering
Perfect	V-ing perfect
I could have altered you could have altered he could have altered we could have altered you could have altered they could have altered	I could have been altering you could have been altering he could have been altering we could have been altering you could have been altering they could have been altering

Negation

Simple form	V-ing form
I could not alter you could not alter he could not alter we could not alter you could not alter they could not alter	I could not be altering you could not be altering he could not be altering we could not be altering you could not be altering they could not be altering
Perfect	V-ing perfect
I could not have altered you could not have altered he could not have altered we could not have altered you could not have altered they could not have altered	I could not have been altering you could not have been altering he could not have been altering we could not have been altering you could not have been altering they could not have been altering

Interrogative form

Simple form	V-ing form
could I alter? could you alter? could he alter? could we alter? could you alter? could they alter?	could I be altering? could you be altering? could he be altering? could we be altering? could you be altering? could they be altering?
Perfect	V-ing perfect
could I have altered? could you have altered? could he have altered? could we have altered? could you have altered? could they have altered?	could I have been altering? could you have been altering? could he have been altering? could we have been altering? could you have been altering? could they have been altering?

Interro-negative form

Simple form	V-ing form
could I not alter? could you not alter? could he not alter? could we not alter? could you not alter? could they not alter?	could I not be altering? could you not be altering? could he not be altering? could we not be altering? could you not be altering? could they not be altering?
Perfect	V-ing perfect
could I not have altered? could you not have altered? could he not have altered? could we not have altered? could you not have altered? could they not have altered?	could I not have been altering? could you not have been altering? could he not have been altering? could we not have been altering? could you not have been altering? could they not have been altering?