could sum
Verbo regular: sum - summed- summed

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could sum
you could sum
she could sum
we could sum
you could sum
they could sum 	I could be summing
you could be summing
she could be summing
we could be summing
you could be summing
they could be summing	I could have summed
you could have summed
she could have summed
we could have summed
you could have summed
they could have summed	I could have been summing
you could have been summing
she could have been summing
we could have been summing
you could have been summing
they could have been summing	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could not sum
you could not sum
she could not sum
we could not sum
you could not sum
they could not sum 	I could not be summing
you could not be summing
she could not be summing
we could not be summing
you could not be summing
they could not be summing	I could not have summed
you could not have summed
she could not have summed
we could not have summed
you could not have summed
they could not have summed	I could not have been summing
you could not have been summing
she could not have been summing
we could not have been summing
you could not have been summing
they could not have been summing	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I sum?
could you sum?
could she sum?
could we sum?
could you sum?
could they sum? 	could I be summing?
could you be summing?
could she be summing?
could we be summing?
could you be summing?
could they be summing? 	could I have summed?
could you have summed?
could she have summed?
could we have summed?
could you have summed?
could they have summed? 	could I have been summing?
could you have been summing?
could she have been summing?
could we have been summing?
could you have been summing?
could they have been summing? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I not sum?
could you not sum?
could she not sum?
could we not sum?
could you not sum?
could they not sum? 	could I not be summing?
could you not be summing?
could she not be summing?
could we not be summing?
could you not be summing?
could they not be summing? 	could I not have summed?
could you not have summed?
could she not have summed?
could we not have summed?
could you not have summed?
could they not have summed? 	could I not have been summing?
could you not have been summing?
could she not have been summing?
could we not have been summing?
could you not have been summing?
could they not have been summing?