could alter
Regular verb: alter - altered- altered

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
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	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 	Perfect 	V-ing perfect 	
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	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 	Perfect 	V-ing perfect 	
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? 	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 	Perfect 	V-ing perfect 	
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? 	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?