So much has been written on both the doctrinal detail and broad themes of Aquinas' Trinitarian theology, a contemporary investigator setting himself the task of examining a point of basic perspective in this theology assumes the burden of proof that the examination is really called for. One would think, for instance, that the Thomist concept of theological science, its methodological ideal, the scope and limitations of rational process within this ideal, were all questions that had been more or less settled by previous criticism. The fact is that only recently no less a scholar than Dom Cyprian Vagaggini, in a contribution to the Anselmian commemorative volume Spicilegium Beccense (Paris 1959) confronted the traditional interpretation of St. Thomas' Trinitarian expositions with a most interesting and academically stimulating challenge. As Dom Vagaggini reads the text, St. Thomas reached a point in his more mature works where he had, for every practical purpose, made quite his own St. Anselm's rationes necessariae and the ideal of rational demonstration based on the notion of pure perfections.