How does one define the universe?
St. Thomas argues that the universe can be considered under higher lights: for instance, as possessing the good of a unity of order with God as its separate, common good. (See St. Thomas, In Meta., lib. XII, lect. 12, nn. 2629–37.) However, it seems that there are three moments in speculative philosophy where the universe is defined through its formative principles. Each of these brushes with “the all” paint the universe under the light of a “unity of order” or a “totality of consistently interacting things and their very unity.” (Jaki, “Thomas and the Universe,” 545)
First, in general natural philosophy, the universe is defined as a unity of order among mobile beings in place and time grounded by a fundamental physical agency, the primum mobile. This defines the universe in reference to its fundamental constituents of order and agency. Second, in the study of the soul—and this is especially so if one incorporates an updated version of Thomistic psychology that includes evolution—one sees that lower substances are essentially ordered to the human substance (and even so ordered in time given evolution as a hypothesis).—(De Koninck defends this thesis in his unfinished work, The Cosmos; see in particular 263–68, 287–88. Here I note that De Koninck places his treatment of evolution in the cosmos on a hypothetic footing; ibid., 262–63: “An important point for the form under which we treat this question is that from the existence of the first composite (supposing that the world had a beginning in time) all possible natural forms were given in the potency of prime matter.” My emphases.)—This defines the universe (or, the physical universe, at least) in reference to the noblest part that serves as its end. Finally, metaphysics defines the universe according to the most encompassing note of the unity of its order in reference to its extra-cosmic agency and ultimate telos.
It is striking that the grand triad of German idealism (God, the world-whole, and the soul) find parallels in perennial philosophy. However, the universe does not enter into perennial philosophy as a regulative idea that is part of a system comprehended by the ghostly transcendental mind. Rather, the mind enters into the universe through no fewer that three separate approaches—touching upon but not encompassing its totality and ultimate principle.