could letter
Regular verb: letter - lettered- lettered

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could letter
you could letter
he could letter
we could letter
you could letter
they could letter 	I could be lettering
you could be lettering
he could be lettering
we could be lettering
you could be lettering
they could be lettering	I could have lettered
you could have lettered
he could have lettered
we could have lettered
you could have lettered
they could have lettered	I could have been lettering
you could have been lettering
he could have been lettering
we could have been lettering
you could have been lettering
they could have been lettering	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could not letter
you could not letter
he could not letter
we could not letter
you could not letter
they could not letter 	I could not be lettering
you could not be lettering
he could not be lettering
we could not be lettering
you could not be lettering
they could not be lettering	I could not have lettered
you could not have lettered
he could not have lettered
we could not have lettered
you could not have lettered
they could not have lettered	I could not have been lettering
you could not have been lettering
he could not have been lettering
we could not have been lettering
you could not have been lettering
they could not have been lettering	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I letter?
could you letter?
could he letter?
could we letter?
could you letter?
could they letter? 	could I be lettering?
could you be lettering?
could he be lettering?
could we be lettering?
could you be lettering?
could they be lettering? 	could I have lettered?
could you have lettered?
could he have lettered?
could we have lettered?
could you have lettered?
could they have lettered? 	could I have been lettering?
could you have been lettering?
could he have been lettering?
could we have been lettering?
could you have been lettering?
could they have been lettering? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I not letter?
could you not letter?
could he not letter?
could we not letter?
could you not letter?
could they not letter? 	could I not be lettering?
could you not be lettering?
could he not be lettering?
could we not be lettering?
could you not be lettering?
could they not be lettering? 	could I not have lettered?
could you not have lettered?
could he not have lettered?
could we not have lettered?
could you not have lettered?
could they not have lettered? 	could I not have been lettering?
could you not have been lettering?
could he not have been lettering?
could we not have been lettering?
could you not have been lettering?
could they not have been lettering?