English verb conjugation
CAN FAIL

Regular verb: fail - failed - failed

Affirmation

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

Negation

Simple form	V-ing form
I can't fail you can't fail he can't fail we can't fail you can't fail they can't fail	I can't be failing you can't be failing he can't be failing we can't be failing you can't be failing they can't be failing
Perfect	V-ing perfect
I can't have failed you can't have failed he can't have failed we can't have failed you can't have failed they can't have failed	I can't have been failing you can't have been failing he can't have been failing we can't have been failing you can't have been failing they can't have been failing

Interrogative form

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

Interro-negative form

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