The doctrine of the Trinity, proclaimed by Christians through the Nicene-Constantinople creed, is foundational to traditional Christian belief and worship of God. But is this doctrine logically coherent? How can there be three divine persons (Father, Son, and Holy Spirit), each is God, and yet there is only one God? This is a fundamental question for philosophers, but theologians have additional questions. This Element addresses philosophical and theological issues concerning the Trinity: Hermeneutical and Logical problems, Personal Pronouns, Monarchy, Equality, the Greek vs. Latin filioque debate, Real Relations, Unity of Action, Self-Knowledge in the Trinity, and Simplicity. Based on my recent rediscovery of the sixth ecumenical council's (Constantinople III) clarifications of Trinitarian doctrine, this Element introduces Conciliar Trinitarianism and shows how it responds to the issues, including a resolution to the fundamental logical question. It also compares Conciliar Trinitarianism with Miaphysite, neo-Sabellian, Social, and other models of the Trinity.
