some that exist through themselves and others that exist through something else. You may consider this with respect to each existing thing individually and with respect to the totality, and say:

It is impossible for any individual existing thing to exist through something nonexistent. For if every existing thing existed through something nonexistent, it would follow that each existing thing existed through a nonexistent thing, which is impossible. Since this is impossible, either every existing thing exists through itself or it exists through something nonexistent; the latter is impossible. Since this is impossible, either every existing thing exists through itself, or every existing thing exists through the existence of another, or some exist through themselves while others exist through the existence of another.

The first alternative is impossible because there are things that have come into existence and do not exist through themselves.

The second alternative is impossible because, if every single existing thing existed through the existence of another, and that other were itself among the existing things that exist only through another existent being, then there would be nothing among them except things dependent upon and in need of another. Whatever is intrinsically dependent upon and in need of another exists only through the existence of that other. And whatever cannot itself exist except through another is all the more incapable of independently bringing another into existence. It would therefore follow that, among existing things, none exists through itself and none brings another into existence. It would then follow that none of the existing things exists, since an existent being exists either through itself or through the existence of another. This consequence follows only from the assumption that every existing thing exists through something else.