I can warn you can warn she can warn we can warn you can warn they can warn
V-ing form
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
I can have warned you can have warned she can have warned we can have warned you can have warned they can have warned
V-ing perfect
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
I can't warn you can't warn she can't warn we can't warn you can't warn they can't warn
V-ing form
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
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
V-ing perfect
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
can I warn? can you warn? can she warn? can we warn? can you warn? can they warn?
V-ing form
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
can I have warned? can you have warned? can she have warned? can we have warned? can you have warned? can they have warned?
V-ing perfect
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
can't I warn? can't you warn? can't she warn? can't we warn? can't you warn? can't they warn?
V-ing form
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
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?
V-ing perfect
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?