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 couldn't alter you couldn't alter he couldn't alter we couldn't alter you couldn't alter they couldn't alter	I couldn't be altering you couldn't be altering he couldn't be altering we couldn't be altering you couldn't be altering they couldn't be altering
Perfect	V-ing perfect
I couldn't have altered you couldn't have altered he couldn't have altered we couldn't have altered you couldn't have altered they couldn't have altered	I couldn't have been altering you couldn't have been altering he couldn't have been altering we couldn't have been altering you couldn't have been altering they couldn't 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
couldn't I alter? couldn't you alter? couldn't he alter? couldn't we alter? couldn't you alter? couldn't they alter?	couldn't I be altering? couldn't you be altering? couldn't he be altering? couldn't we be altering? couldn't you be altering? couldn't they be altering?
Perfect	V-ing perfect
couldn't I have altered? couldn't you have altered? couldn't he have altered? couldn't we have altered? couldn't you have altered? couldn't they have altered?	couldn't I have been altering? couldn't you have been altering? couldn't he have been altering? couldn't we have been altering? couldn't you have been altering? couldn't they have been altering?