Those who believe there is a real distinction(122) between the essence and the existence of all actually existing contingent beings mean by this that the real essence which comes into actual existence by creation, or by the action of created causes, is a reality distinct from the existence whereby it actually exists. The actually existing essence is the total term of the creative or productive act; but what we apprehend in it under the concept of _essence_ is really distinct from what we apprehend in it under the concept of _existence_: the existence being a real principle which _actualizes_ the essence, and this latter being itself another real principle which is in itself a positive, subjective _potentiality_ of existence.(123) Neither, of course, can actually exist without the other: no actual existence except that of a real essence; no existing essence except by reason of the existence which makes it actual. But these two real principles of existing contingent being, inseparable as they are and correlative, are nevertheless distinct realities—distinct in the objective order and independently of our thought,—and form by their union a really _composite_ product: the existing thing. We might attempt to illustrate this by the analogy of a body and its shape or colour. The body itself is really distinct from its actual shape and colour: it may lose them, and yet remain the same body; and it may acquire other shapes and colours. At any time the body has actually some particular shape and colour; but that by which it is formally so shaped and coloured is something really different from the body itself. Furthermore, before the body _actually_ possessed this particular shape and colour, these were in it _potentially_: that is to say, there were then in the body the real, passive, subjective potentialities of this particular shape and colour. So too _that by which_ a real (contingent) essence actually exists (_i.e._ the existential _act_, existence) is really distinct from _that which_ actually exists (_i.e._ the essence, the _potentiality_ of that existential act). The analogy is, however, at best only a halting one. For while it is comparatively easy to understand how the passive, subjective _potentiality_ of a shape or colour can be _something real_ in the _already actually existing_ body, it is not so easy to understand how the _potentiality of existence_, _i.e._ the real essence, can be anything that is itself real and really distinct from the existence.(124) The oak is _really_ in the acorn, for the passive, subjective potentiality of the oak is in the actual acorn; but is this potentiality anything really distinct from the acorn? or should we not rather say that the _actual_ acorn _is potentially_ the oak, or _is_ the potentiality of the oak? At all events even if it is really distinct from the actual acorn, it is in the actual acorn.