trichotomy, law of See CHOICE SEQUENCE, RELA -. TIO. Trinitarianism, the theological doctrine that God consists of three persons. The persons who constitute the Holy Trinity are the Father; the Son, who is Jesus Christ; and the Holy Spirit (or Holy Ghost). The doctrine states that each of these three persons is God and yet they are not three Gods but one God. According to a traditional formulation, the three persons are but one substance. In the opinion of Aquinas, the existence of God can be proved by human reason, but the existence of the three persons cannot be proved and is known only by revelation. According to Christian tradition, revelation contains information about the relations among the three persons, and these relations ground proper attributes of each that distinguish them from one another. Thus, since the Father begets the Son, a proper attribute of the Father is paternity and a proper attribute of the Son is filiation. Procession (or spiration) is a proper attribute of the Holy Spirit. A disagreement about procession has contributed to dividing Eastern and Western Christianity. The Eastern Orthodox church teaches that the Holy Spirit proceeds from the Father through the Son. A theory of double procession according to which the Holy Spirit proceeds from the Father and the Son has been widely accepted in the West. This disagreement is known as the filioque (‘and the Son’) controversy because it arose from the fact that adding this Latin phrase to the Nicene Creed became acceptable in the West but not in the East. Unitarianism denies that God consists of three persons and so is committed to denying the divinity of Jesus. The monotheistic faiths of Judaism and Islam are unitarian, but there are unitarians who consider themselves Christians. See also PHILOSOPHY OF RELIGIO. P.L.Q.