English verb conjugation
COULD WARN

Regular verb: warn - warned - warned

Affirmation

Simple form	V-ing form
I could warn you could warn she could warn we could warn you could warn they could warn	I could be warning you could be warning she could be warning we could be warning you could be warning they could be warning
Perfect	V-ing perfect
I could have warned you could have warned she could have warned we could have warned you could have warned they could have warned	I could have been warning you could have been warning she could have been warning we could have been warning you could have been warning they could have been warning

Negation

Simple form	V-ing form
I couldn't warn you couldn't warn she couldn't warn we couldn't warn you couldn't warn they couldn't warn	I couldn't be warning you couldn't be warning she couldn't be warning we couldn't be warning you couldn't be warning they couldn't be warning
Perfect	V-ing perfect
I couldn't have warned you couldn't have warned she couldn't have warned we couldn't have warned you couldn't have warned they couldn't have warned	I couldn't have been warning you couldn't have been warning she couldn't have been warning we couldn't have been warning you couldn't have been warning they couldn't have been warning

Interrogative form

Simple form	V-ing form
could I warn? could you warn? could she warn? could we warn? could you warn? could they warn?	could I be warning? could you be warning? could she be warning? could we be warning? could you be warning? could they be warning?
Perfect	V-ing perfect
could I have warned? could you have warned? could she have warned? could we have warned? could you have warned? could they have warned?	could I have been warning? could you have been warning? could she have been warning? could we have been warning? could you have been warning? could they have been warning?

Interro-negative form

Simple form	V-ing form
couldn't I warn? couldn't you warn? couldn't she warn? couldn't we warn? couldn't you warn? couldn't they warn?	couldn't I be warning? couldn't you be warning? couldn't she be warning? couldn't we be warning? couldn't you be warning? couldn't they be warning?
Perfect	V-ing perfect
couldn't I have warned? couldn't you have warned? couldn't she have warned? couldn't we have warned? couldn't you have warned? couldn't they have warned?	couldn't I have been warning? couldn't you have been warning? couldn't she have been warning? couldn't we have been warning? couldn't you have been warning? couldn't they have been warning?