This paper introduces Phenomenological Thomism by accomplishing the three tasks Thomas Aquinas sets for every prooemium. First, to promote goodwill (beniuolus), it shows how fruitful Phenomenological Thomism promises to be by arguing that it unites the strengths of two complementary alternatives to the modern starting point. Second, to make teachable (docilis), it delineates the principal vectors of phenomenological engagement, including philosophy of nature, philosophical anthropology, ethics, epistemology, metaphysics, philosophical theology, and revealed theology. Third, to arouse attention (attentus), it focuses on the theme of manifestation to highlight the challenge of bringing the two traditions together. In this way, the prooemium encourages the further development of Phenomenological Thomism as a research program involving countless scholars and an infinity of tasks.

The development of Thomas’s teaching on Christ’s headship relies upon the principle of the causality of the maximum: ‘the maximum in a genus is the universal cause in that genus’. This principle appears in the fourth way to demonstrate God’s existence. Applied to the humanity of Christ, Thomas argues that Christ, on account of his perfect fullness of grace, is, according to his humanity, the universal source of grace for all the members of the Church, including the angels. How does this cohere with Thomas’s teaching elsewhere in the Summa theologiae that it is only as Word that Christ causes grace in the angels? In this paper, I explore this tension and offer a way of understanding Thomas’s broader approach to the mystery of Christ.