English verb conjugation
CAN WARN

Regular verb: warn - warned - warned

Affirmation

Simple form	V-ing form
I can warn you can warn he can warn we can warn you can warn they can warn	I can be warning you can be warning he 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 he 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 he 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 he 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 he 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 he 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 he 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 he warn? can we warn? can you warn? can they warn?	can I be warning? can you be warning? can he 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 he 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 he 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 he 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 he 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 he 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 he have been warning? can't we have been warning? can't you have been warning? can't they have been warning?