It certainly must have required a wonderful effort of imagination on the part of Dr. Warren to transform "weight" and "density," mere passive affections of matter, into self-activity, intelligence, thought, and design. Weight or density are merely relative terms. Supposing one particle or mass of matter to exist alone, and there can be no attractive or gravitating force. There must be a cause of gravity which is distinct from matter.] 3d. The validity of "_the principle of unity_" is also discredited by Watson. "If, however, it were conceded that some glimmerings of this great truth, the existence of a First Cause, might, by induction, have been discovered, by what means could they have demonstrated to themselves that the great collection of bodies which we call the world had but _one_ Creator."[369] [Footnote 369: "Institutes of Theology," vol. i. p. 275.] We might answer directly, and at once, that the oneness or unity of God is necessarily contained in "the very notion of a First Cause"--a _first_ cause is not many causes, but _one_. By a First Cause we do not, however, understand the first of a numerical series, but an ἀρχή--a principle, itself unbeginning, which is the source of all beginning. Our categorical answer, therefore, must be that the unity of God is a sublime deliverance of reason--God is one God. It is a first principle of reason that all differentiation and plurality supposes an incomposite unity, all diversity implies an indivisible identity. The sensuous perception of a plurality of parts supposes the rational idea of an absolute unity, which has no parts, as its necessary correlative. For example, extension is a congeries of indefinitesimal parts; the continuity of matter, as _empirically_ known by us, is never absolute. Space is absolutely continuous, incapable of division into integral parts, illimitable, and, as _rationally_ known by us, an absolute unity. The cognition of limited extension, which is the subject of quantitative measurement, involves the conception of unlimited space, which is the negation of all plurality and complexity of parts. And so the cognition of a phenomenal universe in which we see only difference, plurality, and change, implies the existence of a Being who is absolutely unchangeable, identical, and one.