podcast 271 – Does your Trinity theory require relative identity?

Apologists, this episode is for you. Some of you hold a Trinity theory which will clearly be incoherent unless relative identity theory is true. In this episode, I explain the concept of (numerical) identity, the basic idea behind Catholic analytic philosopher Peter Geach’s relative identity theory, and how all of this applies to Trinity theories. It will help you to start to consider whether or not relative identity is a price you’re willing to pay.

Along the way I discuss this argument, which I think we should agree must be unsound. But the question is: Why? (Most philosophers agree that it is obviously valid.)

1. The Father just is God.
2. The Son just is God.
3. Therefore, the Son is the Father (and vice-versa).

And in the last segment I discuss this challenging argument, which interestingly, both me and some trinitarians would say is sound (i.e. it is valid and the premises are true, so the conclusion is true too).

1. The Father and the Son have simultaneously and/or timelessly differed. (theological and biblical premise)
2. Nothing can either simultaneously or timelessly be and not be some way. (self-evident premise)
3. Therefore, Father and the Son are not numerically one thing. (1,2)
4. For any a and any b, and any type of thing F, a and b are the same F only if a and b are numerically one thing. (self-evident premise)
5. Therefore, the Father and the Son are not the same god. (3, 4)

But what do you say about this argument? That’s the point.

(In this episode I don’t discuss Brower’s and Rea’s sort of non-Geachian relative identity theory, on which see this.)

Links for this episode:

• Identity
• “Trinity,” Stanford Encyclopedia of Philosophy
• Peter van Inwagen, “Not by Confusion of Substance But by Unity of Person,” “And Yet They Are Not Three Gods But One God”
• the apologetics blind-spot on numerical identity
• On Numerical Sameness / Identity / “Absolute” Identity
• podcast 28 – Interview with Dr. William Hasker about his Metaphysics and the Tripersonal God – Part 2
• podcast 27 – Interview with Dr. William Hasker about his Metaphysics and the Tripersonal God – Part 1
• podcast 231 – Swinburne’s Social Theory of the Trinity
• This week’s thinking music is “Two Pianos” by Stefan Kartenberg.