This study works through an argument in analytic theology for the necessity of the Trinity — not merely its coherence, but why God being triune is not an arbitrary fact, the way it might be arbitrary that God chose to make one sun rather than two. The argument is adapted from a 2021 article by the philosopher Joshua Reginald Sijuwade, "Love and the Necessity of the Trinity: An A Posteriori Argument," published open access in the journal Religions (vol. 12, article 990, under a Creative Commons Attribution license). Sijuwade builds on, and reformulates, an older argument from the philosopher Richard Swinburne, so we begin with Swinburne's version before seeing why Sijuwade thought it needed rebuilding.
The doctrine, stated carefully
The Trinity is the Christian teaching that one God exists as three persons — Father, Son, and Holy Spirit (Greek: hypostases) — each fully sharing the one divine nature (Greek: ousia). It is not three gods, and it is not one person wearing three masks. It is one what and three whos.
The question this study addresses is narrower and more technical than "is the Trinity true?" or even "is the Trinity coherent?" It is: if there is a single divine person, is it necessarily true that two others exist? If the answer is yes, then the Trinity is not simply revealed as a brute fact to be accepted — it is the kind of thing that follows from what God's nature already is.
Swinburne's Love Argument
Swinburne's case, following the medieval theologian Richard of St. Victor, runs like this. Suppose there exists a solitary divine person — an essentially, everlastingly omnipotent being. Perfect love, Swinburne argues, has two necessary features:
- Mutuality — a total sharing of oneself with an equal, reciprocated in kind, the way a good marriage involves each spouse giving the other what is good for them.
- Unselfishness — a love that does not remain closed between two people but actively seeks to include a third in what is shared, the way a loving couple often desires to extend their family.
If perfect love requires both of these, then a single divine person cannot fully exemplify it alone — there is no one to love mutually. So this person has an "overriding reason" (a reason that makes an action not just good but the one a perfectly good being must take) to generate a second divine person, an equal, so mutual love becomes possible. And two divine persons loving each other only mutually would still be missing something — the unselfish reach outward — so together they generate a third, so that each has someone to love and be loved by beyond the pair.
On this argument, the existence of three divine persons is not a decision God makes freely, the way God freely decides to create a universe. It follows necessarily from what perfect love is, once you grant that a perfectly good, omnipotent being exists. And crucially, for Swinburne, this is knowable a priori — by thinking carefully about the nature of love, independent of any empirical investigation of the world.
The Intuition Objection
Here is the difficulty. The whole argument leans on a specific claim: that mutuality and unselfishness are the "great-making," essential features of perfect love — rather than, say, self-sufficiency, or some other quality entirely. Swinburne offers this as something we should simply see to be true on reflection. But intuitions are not self-certifying. The philosopher Harry Frankfurt, for instance, has argued that self-love, not other-directed love, is the truest form of love. Nothing in the argument itself rules that reading out except Swinburne's own sense of what love must be like.
So a sympathetic critic can grant every later step of the argument and still ask the question that undoes it at the root: why these two features, rather than some other conception of love that carries no Trinitarian implications at all? Without an answer, the "necessary truth" of the Trinity turns out to rest on one philosopher's intuition — which is a thin foundation for a claim this large.
This is the problem Sijuwade sets out to solve — not by abandoning the Love Argument, but by rebuilding its foundation on something other than intuition: an empirical, revealed fact about what love actually is, combined with a specific philosophical tool for turning empirical facts into necessary truths. That tool is the subject of the next study.
Why it matters
Even before the technical reconstruction, the shape of Swinburne's argument is worth sitting with on its own: it treats the Trinity not as a puzzle to be defended against the charge of incoherence, but as the expected shape of a God who is, in his very nature, love. If that argument can be made to stand, it changes what it means to worship a triune God — not "God happens to exist as three," but "a God who is truly loving could not have existed any other way."