Another circumstance that has led to the belief in the disappearance of books of rules is the observation that from those books dealing with the so-called _arts,_ there has come to be a treatment of the philosophy of their subject-matter, in which those treatises have been dissolved. Thus from Poetics and Rhetorics has come Æsthetic, from Grammatic the Philosophy of language, from the Art of teaching and of reasoning Logic and Gnoseology, from the historical Art, Historic, from the Arts of economic government, the Science of Economy, from the treatises on Natural Law, the Philosophy of Law. When such philosophies, then, had appeared, treatises upon the Arts seemed to have become superfluous, and to this is attributed the cause of their diminution or disappearance. But although it be impossible not to recognize the historical process above described from books on the arts to books of systems, it is necessary to be careful to interpret it exactly and not to confuse it with a passing from empiria to philosophy. Thus it will be seen that the part absorbed and dissolved in philosophy has been precisely those philosophical attempts that were mingled with such collections of rules and precepts. For it was very natural that the writers who put them together and had ideas as to what should be done and what avoided, were often led to investigate the principles from which sprung the particular rules. Believing that they were strengthening, they really came to surpass them, that is, they passed unwittingly from one form of treatment to another, from Psychology to Philosophy. But not even here has empiricism been refined into philosophy (a refinement which, strictly speaking, is impossible), but a more perfect philosophy has been substituted for one less perfect. The dissolution, then, has not been of the rules, but of that imperfect philosophy, a chemical process which has left the rules in what they possess of original as residuum. Hence their persistence, and indeed the impossibility that they should not persist, side by side with the most pure and perfect of philosophies. [Sidenote: _Casuistic: its nature and utility._]