Anselm's Proof that God is One and Three in Monologion XXXVIII–LX: Ontology and the Future of Philosophical Cosmology

Introduction and Thesis

Anselm's attempt to prove the doctrine of the Trinity by reason alone (sola ratione) invites questions about the relation of faith to reason and of philosophy to theology. Many, especially those who have studied Aquinas, are accustomed to regard matters Trinitarian as theological questions that lie beyond the limits of philosophy. For Aquinas, the truth of the matter lies beyond the demonstrative capacities of unaided human reason. One must obediently accept that God is triune on the authority of Scripture and tradition and, just as important, carefully keep in check any further purely philosophical speculation on the matter. It is little wonder then that a premier Thomistic philosopher of the 20th century, Etienne Gilson, once characterized Anselm's project as reckless rationalism.¹

Aquinas' reasons for excluding consideration of the Trinity within the limits of reason alone were partly prudential (failure to prove what one states one can prove will weaken the faith) and partly epistemological (cause and effect reasoning cannot illuminate the immanent life and nature of God). Anselm shared Aquinas' prudential caution; one need only note the tentativeness with which he explains his project of proceeding sola ratione, his deference to previous authorities (especially Augustine), and his frequent confession of the limits of his arguments throughout the Monologion. But apparently, he did not share Aquinas' epistemological reservations; while speaking of the summa natura and the word (verbum) that it utters, Anselm states: "in respect of the fact that it does not derive existence from that word, but that word from him, they admit of an ineffable plurality, ineffable certainly, for although necessity requires that they be two, it can in no wise be explained why they are two."² Confessions of ineffability certainly moderate Anselm's recklessness; but, for present purposes, the key point is that it is necessity rather than authority that requires their plurality.

The question I consider in this essay is not about the relationship between faith and reason. I will not address the methodological considerations involved in distinguishing philosophy from theology as distinct academic disciplines. The epistemological differences that might explain why Anselm believes that the Trinity is subject to rational demonstration and why Aquinas does not, are also beyond the scope of the essay. Like Aquinas, I think Anselm's argument fails. Since Anselm abandons any attempt to demonstrate the Trinity in Proslogion, perhaps he came to share this assessment. My question is about why the argument fails on metaphysical rather than on epistemological grounds.

My thesis is that the argument fails, indeed is bound to fail, because Anselm begins with an ontology that is completely non-relational and that must, even at a purely conceptual level, exclude any otherness and thereby any duality (or trinity) in the divinity. Having made that case, I will take up the question about the division of labor between philosophy and theology that became the standard (especially for philosophers and theologians within or strongly influenced by the revival of Thomism in the 19th and 20th centuries) at the end of the essay to suggest that Anselm's is a model better suited for configuring the interplay of contemporary theology and philosophical cosmology.

Non-Relational Realism: The Ontology of Boethius and Anselm

First, a definition: The phrase non-relational ontology refers to any metaphysical system in which "to be" means "to be what one is apart from any relation to anything other than oneself." Parmenides is the prime example of non-relational ontology: being is and it is impossible that it not be in any respect. Were there more than one such being, the second would not be the first and thereby differ from it, that is, not be it—in which case being would not-be in at least one respect. For the same reason, being can admit of no intrinsic distinctions, for the whole is not the part. Democritean atoms are Parmenides' "being" writ small: there are many of them, and they have extension...