I could caution you could caution he could caution we could caution you could caution they could caution
V-ing form
I could be cautioning you could be cautioning he could be cautioning we could be cautioning you could be cautioning they could be cautioning
Perfect
I could have cautioned you could have cautioned he could have cautioned we could have cautioned you could have cautioned they could have cautioned
V-ing perfect
I could have been cautioning you could have been cautioning he could have been cautioning we could have been cautioning you could have been cautioning they could have been cautioning
Negation
Simple form
I could not caution you could not caution he could not caution we could not caution you could not caution they could not caution
V-ing form
I could not be cautioning you could not be cautioning he could not be cautioning we could not be cautioning you could not be cautioning they could not be cautioning
Perfect
I could not have cautioned you could not have cautioned he could not have cautioned we could not have cautioned you could not have cautioned they could not have cautioned
V-ing perfect
I could not have been cautioning you could not have been cautioning he could not have been cautioning we could not have been cautioning you could not have been cautioning they could not have been cautioning
Interrogative form
Simple form
could I caution? could you caution? could he caution? could we caution? could you caution? could they caution?
V-ing form
could I be cautioning? could you be cautioning? could he be cautioning? could we be cautioning? could you be cautioning? could they be cautioning?
Perfect
could I have cautioned? could you have cautioned? could he have cautioned? could we have cautioned? could you have cautioned? could they have cautioned?
V-ing perfect
could I have been cautioning? could you have been cautioning? could he have been cautioning? could we have been cautioning? could you have been cautioning? could they have been cautioning?
Interro-negative form
Simple form
could I not caution? could you not caution? could he not caution? could we not caution? could you not caution? could they not caution?
V-ing form
could I not be cautioning? could you not be cautioning? could he not be cautioning? could we not be cautioning? could you not be cautioning? could they not be cautioning?
Perfect
could I not have cautioned? could you not have cautioned? could he not have cautioned? could we not have cautioned? could you not have cautioned? could they not have cautioned?
V-ing perfect
could I not have been cautioning? could you not have been cautioning? could he not have been cautioning? could we not have been cautioning? could you not have been cautioning? could they not have been cautioning?