English verb conjugation
CAN WARN

Regular verb: warn - warned - warned

Affirmation

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

Negation

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

Interrogative form

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

Interro-negative form

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