Shortly[5] after the Reformation, we find two great schools of thought dividing this class of subjects between them. The most influential of the two was at first the sect of school known to us as the Casuists, all of them in spiritual communion with the Roman Catholic Church, and nearly all of them affiliated to one or other of her religious orders. On the other side were a body of writers connected with each other by a common intellectual descent from the great author of the treatise _De Jure Belli et Pacis_, Hugo Grotius. Almost all of the latter were adherents of the Reformation, and though it cannot be said that they were formally and avowedly at conflict with the Casuists, the origin and object of their system were nevertheless essentially different from those of Casuistry. It is necessary to call attention to this difference, because it involves the question of the influence of Roman law on that department of thought with which both systems are concerned. The book of Grotius, though it touches questions of pure Ethics in every page, and though it is the parent immediate or remote of innumerable volumes of formal morality, is not, as is well known, a professed treatise on Moral Philosophy; it is an attempt to determine the Law of Nature, or Natural Law. Now, without entering upon the question, whether the conception of a Law Natural be not exclusively a creation of the Roman jurisconsults, we may lay down that, even on the admission of Grotius himself, the dicta of the Roman jurisprudence as to what parts of known positive law must be taken to be parts of the Law of Nature, are, if not infallible, to be received at all events with the profoundest respect. Hence the system of Grotius is implicated with Roman law at its very foundation, and this connection rendered inevitable--what the legal training of the writer would perhaps have entailed without it--the free employment in every paragraph of technical phraseology, and of modes of reasoning, defining, and illustrating, which must sometimes conceal the sense, and almost always the force and cogency, of the argument from the reader who is unfamiliar with the sources whence they have been derived. On the other hand, Casuistry borrows little from Roman law, and the views of morality contended for have nothing whatever in common with the undertaking of Grotius. All that philosophy of right and wrong which has become famous, or infamous, under the name of Casuistry, had its origin in the distinction between Mortal and Venial Sin. A natural anxiety to escape the awful consequences of determining a particular act to be mortally sinful, and a desire, equally intelligible, to assist the Roman Catholic Church in its conflict with Protestantism by disburthening it of an inconvenient theory, were the motives which impelled the authors of the Casuistical philosophy to the invention of an elaborate system of criteria, intended to remove immoral actions,