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 couldn't fail you couldn't fail he couldn't fail we couldn't fail you couldn't fail they couldn't fail	I couldn't be failing you couldn't be failing he couldn't be failing we couldn't be failing you couldn't be failing they couldn't be failing
Perfect	V-ing perfect
I couldn't have failed you couldn't have failed he couldn't have failed we couldn't have failed you couldn't have failed they couldn't have failed	I couldn't have been failing you couldn't have been failing he couldn't have been failing we couldn't have been failing you couldn't have been failing they couldn't 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
couldn't I fail? couldn't you fail? couldn't he fail? couldn't we fail? couldn't you fail? couldn't they fail?	couldn't I be failing? couldn't you be failing? couldn't he be failing? couldn't we be failing? couldn't you be failing? couldn't they be failing?
Perfect	V-ing perfect
couldn't I have failed? couldn't you have failed? couldn't he have failed? couldn't we have failed? couldn't you have failed? couldn't they have failed?	couldn't I have been failing? couldn't you have been failing? couldn't he have been failing? couldn't we have been failing? couldn't you have been failing? couldn't they have been failing?