a thing actually existent cannot have nothing , or a thing nonexistent, for the cause of its existence.
IV . All the reality of perfection which is in a thing is found formally or eminently in its first and total cause.
V . Whence it follows likewise, that the objective reality of our ideas requires a cause in which this same reality is contained, not simply objectively, but formally or eminently. And it is to be observed that this axiom must of necessity be admitted, as upon it alone depends the knowledge of all things, whether sensible or insensible. For whence do we know, for example, that the sky exists? Is it because we see it? But this vision does not affect the mind unless in so far as it is an idea, and an idea inhering in the mind itself, and not an image depicted on the fantasy; and, by reason of this idea, we cannot judge that the sky exists unless we suppose that every idea must have a cause of its objective reality which is really existent; and this cause we judge to be the sky itself, and so in the other instances.