The third law is that of unity, which implies that the variety of the different moments composing the cosmos must be brought together so as to form a perfect whole. For, first, if the variety of moments, of species and individuals, is requisite in order to express the intensity of the ontological perfection and excellence of the type of the universe, which is the infinite grandeur of God, unity, also, is required, in order to express the simplicity and entirety of the type. In the second place, what would be the cosmos without unity but a numberless and confused assemblage of beings? Hence, whatever may be the variety of the moments and species of the cosmos, they must necessarily be brought together as parts and components of one harmonic whole. The nature of this unity will be gathered from the explanation of the other laws. And first, it begins to be sketched out by the law of continuity. This implies that there should be a certain proportion between each moment of the cosmos, between one species and another, and between the degrees and gradations within the species, all as far as the nature of the terms will permit. Hence, the law embraces two parts:
1st. The necessity of the greatest number of moments and of species, as much as possible alike to each other, without ever being confounded.
2d. The greatest possible number of gradations within the same species, in proportion as individuals partake more or less fully of the species.
To give an instance: the first part of this law explains why substantial creation is composed of, 1st, atoms which do not give any signs of sensitive life; 2d, of brute animals; 3d, of intelligent animals; 4th, of pure spirits. The second part of this law explains why each of the four species just mentioned is developed in gradations almost infinite—minerals composed and recomposed in all possible ways, manifesting forms, properties, and acts altogether different, and some so constantly as to defy any change from the force of nature so far known to man; hence, in force of that immutable type, they are taken by naturalists as so many scientific species, and the fifty-nine or sixty elements which chemistry so far enumerates; animals also, extending so gradually that the ladder of fixed marks, taken by natural philosophers as so many species, begins where the signs of life are almost insensible and dubious, and ends with man; nor is there wanting, as far as it may be known, any of the intermediate steps.
The pure spirits, as we know from revelation, are divided into choirs and legions innumerable, whose successive gradations in quality and number, to us unknown but certain, are unfathomable; and it is most probable that the ladder of pure spirits is higher, beyond measure, than that which we observe in the sensible universe, and that one spirit is far more superior and distant from another spirit than one star from another.
The necessity of this law springs from that of unity. For, if the type of the cosmos be one, each moment and species representing, as it were, a side of that type, there must be as much affinity and proportion between each moment and each species as to pave the way for the law of unity to represent and mirror the entirety and oneness of the type. We say as much affinity as it is possible to produce, because between each moment and each species there is necessarily a chasm which no continuity or affinity can fill up. For instance, between pure animality and pure intelligence there is necessarily a chasm. Man, placed between the two, draws them together as much as possible; yet the necessary distance marking the two distinct natures cannot by any proportion be eliminated, else the natures would be confounded and destroyed.
But variety, brought together by the law of continuity, cannot sufficiently exhibit unity. Hence the necessity of a fourth law, that of communion.
This law implies, 1st, that the terms of the cosmos should be so united together as to act one upon the other, and serve each other for sustenance and development; 2d, that, founded on the law of hierarchy, inferior beings should be so united to superior ones as to be, in a certain sense, transformed into them, the distinctive marks of their respective natures being kept inviolate.