The Trinitarian heresy treating Father, Son, and Holy Spirit as three separate gods (rather than three Persons of one God). The position is the substantive opposite of Modalism / Sabellianism (which collapses three Persons to one). Tritheism over-emphasizes the threeness of the Persons at the expense of the substantive unity of the divine essence; Modalism over-emphasizes the unity at the expense of the substantive distinctions. Both fail orthodox Trinitarian confession. Historic outbreaks of Tritheism include (1) the sixth-century Monophysite Tritheist controversy among Eastern Christians (John Philoponus of Alexandria and his followers, who applied Aristotelian-philosophical species-and-individual categories to the Trinity in a way that produced effectively three divine individuals sharing the divine nature); (2) various medieval and early-modern moments when over-emphasis on the three Persons produced charges of Tritheism; (3) contemporary popular evangelical-charismatic over-emphases that sometimes effectively treat Father, Son, and Spirit as three distinct co-operating gods. The substantive orthodox confession (Athanasian Creed; Westminster Confession II.3) maintains the one divine essence shared by three Persons; the three Persons are not three gods nor three modes but three eternally distinct Persons consubstantial in the one divine essence. The Reformed-confessional tradition is rigorous on both halves: against Modalism, the substantive distinctions between Father, Son, and Spirit are eternal and substantive; against Tritheism, the divine essence is one and not three. The doctrine of perichoresis (Greek perichoresis, mutual indwelling; Latin circumincession) safeguards the substantive unity by maintaining the eternal mutual indwelling of the three Persons in the one divine essence.