This paper demonstrates and develops Peter Thomas Geach’s identity-relativism as an analytic theological theory that provides a promising understanding of the Christian doctrine of the Trinity. According to identity-relativism, it is the case that the Father and the Son are distinct persons while they are the same God, for numerical identity is to be relativized by what is commonly called sortal concepts such as divine persons and God. To show the consistency of this theory, I proceed to the discussion in the following way. In Section 1, I provide an overview of what is called the logical problem of the Trinity and its solutions proposed thus far. In Section 2, I introduce Geach’s identity-relativism as a theory applicable to the Trinity, and show its notable advantage of avoiding both polytheism and modalism in solving the logical problem. In Section 3, based on an account related to counting Gods and its criterion, I propose possible responses to criticisms of identity-relativism and suggest the simplicity of God taken as a sortal concept. In Section 4, by specifying a logical mechanism that enables the compatibility of identity and distinctness between the Father and the Son, I argue that identity-relativism provides a superior explanation to the Trinity in comparison to similar theological accounts such as constitutionalism and the strategy of sameness without identity. Through this series of discussions, I aim to show how to be an identity-relativist about the Trinity, namely how to reconcile the Trinitarian theology with identity-relativism.