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 couldn't caution you couldn't caution he couldn't caution we couldn't caution you couldn't caution they couldn't caution
V-ing form
I couldn't be cautioning you couldn't be cautioning he couldn't be cautioning we couldn't be cautioning you couldn't be cautioning they couldn't be cautioning
Perfect
I couldn't have cautioned you couldn't have cautioned he couldn't have cautioned we couldn't have cautioned you couldn't have cautioned they couldn't have cautioned
V-ing perfect
I couldn't have been cautioning you couldn't have been cautioning he couldn't have been cautioning we couldn't have been cautioning you couldn't have been cautioning they couldn't 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
couldn't I caution? couldn't you caution? couldn't he caution? couldn't we caution? couldn't you caution? couldn't they caution?
V-ing form
couldn't I be cautioning? couldn't you be cautioning? couldn't he be cautioning? couldn't we be cautioning? couldn't you be cautioning? couldn't they be cautioning?
Perfect
couldn't I have cautioned? couldn't you have cautioned? couldn't he have cautioned? couldn't we have cautioned? couldn't you have cautioned? couldn't they have cautioned?
V-ing perfect
couldn't I have been cautioning? couldn't you have been cautioning? couldn't he have been cautioning? couldn't we have been cautioning? couldn't you have been cautioning? couldn't they have been cautioning?