QUATERNITY, or a fourfold structure (together with its multiples—eightfold, twelvefold, etc.), expresses symbolically the nature of the divine and, by extension, describes the structure of the world that mirrors that divinity. Like the other great numerical symbols in its class, quaternity is impersonal; it may stand alone, or it may be associated with the attributes of a personal god. God is one, says Plotinus, and so is the truth of this world. The divine is dual, say the Zoroastrians, and thus one must choose between truth and falseness. Christians say that God is a trinity, a perception that explains for Augustine the threefold nature of human love. Yet others have experienced the divine mystery as a quaternity, and its reality can be dimly perceived in the world's four cardinal directions, the four seasons, the four elements, and the four temperaments of classical thought.

Something of this symbol's...