English verb conjugation
COULD WARN

Regular verb: warn - warned - warned

Affirmation

Simple form	V-ing form
I could warn you could warn he could warn we could warn you could warn they could warn	I could be warning you could be warning he 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 he 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 he 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 could not warn you could not warn he could not warn we could not warn you could not warn they could not warn	I could not be warning you could not be warning he could not be warning we could not be warning you could not be warning they could not be warning
Perfect	V-ing perfect
I could not have warned you could not have warned he could not have warned we could not have warned you could not have warned they could not have warned	I could not have been warning you could not have been warning he could not have been warning we could not have been warning you could not have been warning they could not have been warning

Interrogative form

Simple form	V-ing form
could I warn? could you warn? could he warn? could we warn? could you warn? could they warn?	could I be warning? could you be warning? could he 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 he 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 he 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
could I not warn? could you not warn? could he not warn? could we not warn? could you not warn? could they not warn?	could I not be warning? could you not be warning? could he not be warning? could we not be warning? could you not be warning? could they not be warning?
Perfect	V-ing perfect
could I not have warned? could you not have warned? could he not have warned? could we not have warned? could you not have warned? could they not have warned?	could I not have been warning? could you not have been warning? could he not have been warning? could we not have been warning? could you not have been warning? could they not have been warning?