English verb conjugation
COULD ALTER

Regular verb: alter - altered - altered

Affirmation

Simple form	V-ing form
I could alter you could alter she could alter we could alter you could alter they could alter	I could be altering you could be altering she 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 she 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 she 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 she 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 she 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 she 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 she 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 she alter? could we alter? could you alter? could they alter?	could I be altering? could you be altering? could she 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 she 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 she 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 she 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 she 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 she 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 she not have been altering? could we not have been altering? could you not have been altering? could they not have been altering?