Those who think that the distinction between essence and existence in created things is a real distinction, hold that accidents as such have no existence of their own, that they are actualized by the existence of the substance, or rather of the concrete, composite individual; that since the latter is a real unity—not a mere artificial aggregation of entities, but a being naturally one—it can have only one existence: _Impossibile est quod unius rei non sit unum esse_;(261) that by this one existence the concrete, composite essence of the substance, as affected and determined by its accidents, is actualized. They contend that if each of the principles, whether substantial or accidental, of a concrete individual being had its own existence, their union, no matter how intimate, could not form a natural unitary being, an individual, but only an aggregate of such beings. It is neither the matter, nor the form, nor the corporeal substance apart from its accidents, that exists: it is the substance completely determined by all its accidents and modes that is the proper subject of existence.(262) It alone is actualized, and that by _one_ existence, which is the “ultimate actuality” of the concrete, composite, individual essence: _esse est ultimus actus_. Hence it is too, they urge, that an accident should be conceived not properly as “a being,” but only as that whereby a being is such or such: Accidens non est ens, sed _ens entis_. But it cannot be so conceived if we attribute to it an existence of its own; for then it would be “a being” in the full and proper sense of the word. This is the view of St. Thomas, and of Thomists generally. The arguments in support of it are serious, but not convincing. And the same may be said of the reasons adduced for the opposite view: that existence not being really distinct from essence, accidents in so far as they can be said to have an essence of their own have likewise an existence of their own.