I can exist you can exist he can exist we can exist you can exist they can exist
V-ing form
I can be existing you can be existing he can be existing we can be existing you can be existing they can be existing
Perfect
I can have existed you can have existed he can have existed we can have existed you can have existed they can have existed
V-ing perfect
I can have been existing you can have been existing he can have been existing we can have been existing you can have been existing they can have been existing
Negation
Simple form
I cannot exist you cannot exist he cannot exist we cannot exist you cannot exist they cannot exist
V-ing form
I cannot be existing you cannot be existing he cannot be existing we cannot be existing you cannot be existing they cannot be existing
Perfect
I cannot have existed you cannot have existed he cannot have existed we cannot have existed you cannot have existed they cannot have existed
V-ing perfect
I cannot have been existing you cannot have been existing he cannot have been existing we cannot have been existing you cannot have been existing they cannot have been existing
Interrogative form
Simple form
can I exist? can you exist? can he exist? can we exist? can you exist? can they exist?
V-ing form
can I be existing? can you be existing? can he be existing? can we be existing? can you be existing? can they be existing?
Perfect
can I have existed? can you have existed? can he have existed? can we have existed? can you have existed? can they have existed?
V-ing perfect
can I have been existing? can you have been existing? can he have been existing? can we have been existing? can you have been existing? can they have been existing?
Interro-negative form
Simple form
can I not exist? can you not exist? can he not exist? can we not exist? can you not exist? can they not exist?
V-ing form
can I not be existing? can you not be existing? can he not be existing? can we not be existing? can you not be existing? can they not be existing?
Perfect
can I not have existed? can you not have existed? can he not have existed? can we not have existed? can you not have existed? can they not have existed?
V-ing perfect
can I not have been existing? can you not have been existing? can he not have been existing? can we not have been existing? can you not have been existing? can they not have been existing?