English verb conjugation
COULD FAIL

Regular verb: fail - failed - failed

Affirmation

Simple form	V-ing form
I could fail you could fail he could fail we could fail you could fail they could fail	I could be failing you could be failing he could be failing we could be failing you could be failing they could be failing
Perfect	V-ing perfect
I could have failed you could have failed he 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 he could have been failing we could have been failing you could have been failing they could have been failing

Negation

Simple form	V-ing form
I could not fail you could not fail he 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 he could not be failing we could not be failing you could not be failing they could not be failing
Perfect	V-ing perfect
I could not have failed you could not have failed he 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 he could not have been failing we could not have been failing you could not have been failing they could not have been failing

Interrogative form

Simple form	V-ing form
could I fail? could you fail? could he fail? could we fail? could you fail? could they fail?	could I be failing? could you be failing? could he be failing? could we be failing? could you be failing? could they be failing?
Perfect	V-ing perfect
could I have failed? could you have failed? could he 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 he have been failing? could we have been failing? could you have been failing? could they have been failing?

Interro-negative form

Simple form	V-ing form
could I not fail? could you not fail? could he 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 he not be failing? could we not be failing? could you not be failing? could they not be failing?
Perfect	V-ing perfect
could I not have failed? could you not have failed? could he 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 he not have been failing? could we not have been failing? could you not have been failing? could they not have been failing?