could fail
Verbo regular: fail - failed- failed

Afirmación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could fail
you could fail
she could fail
we could fail
you could fail
they could fail 	I could be failing
you could be failing
she could be failing
we could be failing
you could be failing
they could be failing	I could have failed
you could have failed
she could have failed
we could have failed
you could have failed
they could have failed	I could have been failing
you could have been failing
she could have been failing
we could have been failing
you could have been failing
they could have been failing	

Negación 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
I could not fail
you could not fail
she could not fail
we could not fail
you could not fail
they could not fail 	I could not be failing
you could not be failing
she could not be failing
we could not be failing
you could not be failing
they could not be failing	I could not have failed
you could not have failed
she could not have failed
we could not have failed
you could not have failed
they could not have failed	I could not have been failing
you could not have been failing
she could not have been failing
we could not have been failing
you could not have been failing
they could not have been failing	

Forma interrogativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I fail?
could you fail?
could she fail?
could we fail?
could you fail?
could they fail? 	could I be failing?
could you be failing?
could she be failing?
could we be failing?
could you be failing?
could they be failing? 	could I have failed?
could you have failed?
could she have failed?
could we have failed?
could you have failed?
could they have failed? 	could I have been failing?
could you have been failing?
could she have been failing?
could we have been failing?
could you have been failing?
could they have been failing? 	

Forma interro-negativa 	
Forma simple 	Forma con V-ing 	Perfecto 	Perfecto con V-ing 	
could I not fail?
could you not fail?
could she not fail?
could we not fail?
could you not fail?
could they not fail? 	could I not be failing?
could you not be failing?
could she not be failing?
could we not be failing?
could you not be failing?
could they not be failing? 	could I not have failed?
could you not have failed?
could she not have failed?
could we not have failed?
could you not have failed?
could they not have failed? 	could I not have been failing?
could you not have been failing?
could she not have been failing?
could we not have been failing?
could you not have been failing?
could they not have been failing?