The Essence of Contingent Beings Is Not the Same as That It Is

Contingent beings are indifferent to being and not being, says Aquinas. But whatever has an existentially open essence must receive its existence from another. The essence of cat can receive existence, and you could have the existence of a concrete cat. Or that existence can go away, and the cat can just simply cease to be. There's nothing in the essence of cathood which accounts for its being or guarantees its being.