Book excerpt: Can a philosopher defend the rational warrant for belief in Christianity? Is it reasonable to be religious? Is it philosophically responsible to be a Christian who believes in the mystery of the Trinity? Principles of Catholic Theology explores these questions in a systematic way by considering questions of ultimate explanation. Why not hold that modern atheistic naturalism provides the best explanation of reality? Or, if there is a transcendent first principle that explains all of reality, is it impersonal rather than personal? Contrastingly, if monotheism constitutes the best explanation for created being, how can we reasonably believe in any particular revelation concerning God? What are the criteria for rational belief in revelation? Thomas Joseph White, OP, considers these questions by exploring a series of topics: the transcendentals (existence, oneness, truth, goodness, beauty); rational argument for the existence of God; the immateriality and subsistence after death of the personal soul of the human being; the historical and conceptual coherence of Trinitarian doctrine; and the reasonableness of the natural desire to see God. The aim of Principles of Catholic Theology, Book 2 is to place contemporary natural reason in profound dialogue with the Catholic faith and to think about ways that we can consent to the profound mystery of the Holy Trinity that are in robust concord with the knowledge obtained from philosophical, scientific, and historical sources.