The Logical Problem of the Trinity

Doctoral Dissertation


The doctrine of the Trinity is central to mainstream Christianity. But insofar as it posits “three persons” (Father, Son and Holy Spirit), who are “one God,” it appears as inconsistent as the claim that 1+1+1=1.

Much of the literature on “The Logical Problem of the Trinity,” as this has been called, attacks or defends Trinitarianism with little regard to the fourth century theological controversies and the late Hellenistic and early Medieval philosophical background in which it took shape. I argue that this methodology, which I call “the Puzzle Approach,” produces obviously invalid arguments, and it is unclear how to repair it without collapsing into my preferred methodology, “the Historical Approach,” which sees history as essential to the debate. I also discuss “mysterianism,” arguing that, successful or not, it has a different goal from the other approaches. I further argue that any solution from the Historical Approach satisfies the concerns of the Puzzle Approach and mysterianism anyway.

I then examine the solution to the Logical Problem of the Trinity found in St. Gregory of Nyssa’s writings, both due to his place in the history of the doctrine, and his clarity in explicating what I call “the metaphysics of synergy.” I recast his solution in standard predicate logic and provide a formal proof of its consistency. I end by considering the possibilities for attacking the broader philosophical context of his defense and conclude that the prospects for doing so are dim. In any case, if there should turn out to be any problem with the doctrine of the Trinity at all, it will not be one of mere logical inconsistency in saying that “These Three are One.”


Attribute NameValues
  • etd-04172014-143816

Author Beau Branson
Advisor Richard Cross
Contributor Richard Cross, Committee Chair
Contributor Fr. Brian Daley, SJ, Committee Member
Contributor Peter van Inwagen, Committee Member
Contributor Ted Warfield, Committee Member
Degree Level Doctoral Dissertation
Degree Discipline Philosophy
Degree Name PhD
Defense Date
  • 2014-04-08

Submission Date 2014-04-17
  • United States of America

  • Philosophical Theology

  • Analytic Theology

  • Patristics

  • Trinity

  • Gregory of Nyssa

  • Logic

  • University of Notre Dame

  • English

Record Visibility Public
Content License
  • All rights reserved

Departments and Units


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