could alter
Regular verb: alter - altered- altered

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