“But there are two kinds of sciences. There are those which proceed from the principles known by the natural light of the mind, as arithmetic and geometry. There are others which proceed from principles known by the light of a superior science: as perspective proceeds from principles made known through geometry, and music from principles known through arithmetic. And _sacra doctrina_ is science in this way, because it proceeds from principles known by the light of a superior science or knowledge which is the knowledge belonging to God and the beatified. Thus as music believes the principles delivered to it by arithmetic, so sacred doctrine believes the principles revealed to it from God.” The question then is raised whether _sacra doctrina_ is one science, or many. And Thomas answers, that it is one, by reason of the unity of its formal object. For it views everything discussed by it as divinely revealed; and all things which are subjects of revelation (_revelabilia_) have part in the formal conception of this science; and so are comprehended under _sacra doctrina_, as under one science. Nevertheless it extends to subjects belonging to various departments of knowledge so far as they are knowable through divine illumination. As some of these may be practical and some speculative, it follows that sacred science includes both the practical and the speculative, even as God with the same knowledge knows himself and also the things He makes. “Yet this science is more speculative than practical, because on principle it treats of divine things rather than human actions, which it treats in so far as man by means of them is directed (_ordinatur_) to perfect cognition of God, wherein eternal beatitude consists. This science in its speculative as well as practical functions transcends other sciences, speculative and practical. One speculative science is said to be worthier than another, by reason of its certitude, or the dignity of its matter. In both respects this science surpasses other speculative sciences, because the others have certitude from the natural light of human reason, which may err; but this has certitude from the light of the divine knowledge, which cannot be deceived; likewise by reason of the dignity of its matter, because primarily it relates to matters too high for reason, while other sciences consider only those which are subjected to reason. It is worthier than the practical sciences, which are ordained for an ulterior end; for so far as this science is practical, its end is eternal beatitude, unto which as an ulterior end all other ends of the practical sciences are ordained (_ordinantur_).