that the matters of fact of which it consists are connected with one another through the permanent character of the “subjects” to which they belong as temporary “states” or “modifications.” But this special interpretation of the way in which the facts of experience form a system is no part of our initial postulate as to the general nature of the real; it is simply one among other theories of the concrete character of the universe, and it is for Metaphysics itself to test its merits. Similarly, we should be making an unwarranted addition to our initial postulate about Reality if we identified it with the doctrine of Hume and his followers, according to whom what really exists is _merely_ a series of “impressions and ideas” connected by certain psychological laws of succession, any profounder structural unity of experience being dismissed as a “fiction of the mind.” The secret of the fallacy here lies in the _petitio principii_ committed by the introduction of the word “merely” into our statement. From the identification of reality with psychical facts which somehow form a systematic unity, it does not in the least follow that the _only_ unity possessed by the facts is that of conformity to a certain law or laws of sequence. _That_ all reality consists of psychical facts, and _that_ these facts must form a system, we are, as we have already seen, entitled to assert as a fundamental metaphysical principle which cannot be doubted without falling into contradiction; _how_ they do so we have yet to discover, if we can.