The "I-Thou" Argument for the Trinity: Wherefore Art Thou?

The following thesis typifies a recent current of thought in Trinitarian theology: "The living God can … be thought of only as Father and Son, while a non-trinitarian, purely monotheistic God would in fact have to be declared dead." Such an opinion, it would seem, would have struck twentieth-century Jewish thinker Martin Buber as false. After all, the central message of the Shema is "Hear, O Israel: The Lord our God is one Lord" (Deut 6:4, RSV). Buber did not read this prayer as Trinitarian, but he did have "monotheistic" faith in the living God. Were he alive, Buber might register surprise that the author of the thesis is a major proponent of ecumenical and interreligious dialogue, Walter Cardinal Kasper. Further, Kasper argues to the thesis by way of a reformulation of Buber's own claim: "An I without a Thou is unthinkable."¹ Did Buber simply fail to grasp the universality of his own insight and so apply it to the God beyond the firmament? Or did Kasper overreach?

Kasper presents an iteration of what I call the "I-Thou" argument for the Trinity. The argument is almost always attended by the so-called "Social Analogy," according to which God is contemplated through the iconic similitude of a community of human persons, an analogy disfavored by the influential Fr. Karl Rahner, S.J.² The "I-Thou" argument and the Social Analogy are, however, favored by a wide range of recent and contemporary theologians. For example, Catherine Mowry LaCugna, otherwise appreciative of Rahner, embraces the analogy and even utilizes it to defend the proposition that, if God exists, an economy of salvation (without hierarchical structures) will exist.³ Protestant theologian Jürgen Moltmann argues that the divine unity is not that of a numerically identical substance, but rather, that of the developing relational "at-oneness" of divine persons.⁴ Romanian Orthodox theologian Dumitru Staniloae meditates profoundly on subjects and their adequate objects, contending that God cannot exist except in intersubjectivity.⁵ Joseph Cardinal Ratzinger writes, "At bottom [only] belief in the Trinity, which recognizes the plural in the unity of God, is [the final] elimination of dualism as a means of explaining plurality alongside unity; only through this belief is the positive validation of plurality given a definitive base."⁶

The present article seeks to elaborate and then to evaluate the basic structure of the "I-Thou" argument and, to some extent, the Social Analogy. How well does the "I-Thou" argument serve theological science with respect to the Church's sober confidence about natural reason's capacities, with respect to the loftiness of faith's object, and with respect to theology's remote task of interreligious dialogue? Two critical teachings will serve as norms of the inquiry: (1) natural reason retains the capacity to discover the truth of God's existence and certain of his attributes, and (2) that the truth of the Holy Trinity is a strict mystery.

Elaboration of the Norms for the Inquiry

The First Vatican Council solemnly defines that human reason can discover the truth of God through creatures. No doubt, due to original sin and actual sins, human reason is darkened from that splendor in which it was constituted by God's grace. Notwithstanding, natural reason is a real and discerning light, not a dominating volition to power that by nature fabricates and conceals. The dogma would be beside the point if it regarded human reason only as such and not in its present condition. Moreover, the papal tradition before and after the Council affirms both that natural reason in its present state can come to know God and that such knowledge can be demonstrative.⁷ It can also consist in the informal inference that a farmer makes in wonder at creation; hence, "The fool says in his heart, 'There is no God'" (Ps 14:1; 53:1). The concrete possibility of knowing God's existence with certainty helps account for Scripture's teaching that idolaters and atheists, even those who never encounter God's special covenants, are without excuse (Wis...