English verb conjugation
COULD EXIST

Regular verb: exist - existed - existed

Affirmation

Simple form	V-ing form
I could exist you could exist he could exist we could exist you could exist they could exist	I could be existing you could be existing he could be existing we could be existing you could be existing they could be existing
Perfect	V-ing perfect
I could have existed you could have existed he could have existed we could have existed you could have existed they could have existed	I could have been existing you could have been existing he could have been existing we could have been existing you could have been existing they could have been existing

Negation

Simple form	V-ing form
I couldn't exist you couldn't exist he couldn't exist we couldn't exist you couldn't exist they couldn't exist	I couldn't be existing you couldn't be existing he couldn't be existing we couldn't be existing you couldn't be existing they couldn't be existing
Perfect	V-ing perfect
I couldn't have existed you couldn't have existed he couldn't have existed we couldn't have existed you couldn't have existed they couldn't have existed	I couldn't have been existing you couldn't have been existing he couldn't have been existing we couldn't have been existing you couldn't have been existing they couldn't have been existing

Interrogative form

Simple form	V-ing form
could I exist? could you exist? could he exist? could we exist? could you exist? could they exist?	could I be existing? could you be existing? could he be existing? could we be existing? could you be existing? could they be existing?
Perfect	V-ing perfect
could I have existed? could you have existed? could he have existed? could we have existed? could you have existed? could they have existed?	could I have been existing? could you have been existing? could he have been existing? could we have been existing? could you have been existing? could they have been existing?

Interro-negative form

Simple form	V-ing form
couldn't I exist? couldn't you exist? couldn't he exist? couldn't we exist? couldn't you exist? couldn't they exist?	couldn't I be existing? couldn't you be existing? couldn't he be existing? couldn't we be existing? couldn't you be existing? couldn't they be existing?
Perfect	V-ing perfect
couldn't I have existed? couldn't you have existed? couldn't he have existed? couldn't we have existed? couldn't you have existed? couldn't they have existed?	couldn't I have been existing? couldn't you have been existing? couldn't he have been existing? couldn't we have been existing? couldn't you have been existing? couldn't they have been existing?