A Formulation of Bonaventure’s Ontological Argument


Image Source: Wikipedia “Bonaventure

<<Si Deus est Deus, Deus est.>>

Bonaventure writes the following argument:

No one can be ignorant of the fact that this is true: the best is the best; or think that it is false. But the best is a being which is absolutely complete. Now any being which is absolutely complete, for this very reason, is an actual being. Therefore, if the best is the best, the best is. In a similar way, one can argue: If God is God, then God is. Now the antecedent is so true that it cannot be thought not to be. Therefore, it is true without doubt that God exists (Bonaventure, De mysterio trinitatis 1.1 fund. 29 (ed. Quaracchi V 48).

The overly-simplified version of the argument is:

P1) If God is God, then God is.

P2) God is God.

C) God is.

Noone and Houser (2013) write, “…the premise If God is God is not an empty tautology (Seifert 1992, 216–217). It means ‘if the entity to which the term God refers truly possesses the divine essence.’ And the conclusion means that such an entity must exist.”  This inspired me to reconstruct Bonaventure’s argument as best I can.

Informally the argument is:

D1) “God” is the absolutely complete being.
P1) There is an object to which the term “God” refers.
P2) If the object to which the term “God” refers does not truly and completely possess the divine essence, then God is not absolutely complete.
P3) If object to which the term “God” refers truly and completely possesses the divine essence, then God exists in reality.
C) God, the being who truly and completely possesses the divine essence, exists in reality.
Explanation of D1: Here we stipulate that God is defined as complete in every positive simple attribute, which is to say that by “God”, we mean a perfect being. This definitions is a definite description, i.e. it refers to a singular term, since absolute completeness implies omnipotence, and there can only be one omnipotent being. For, if there were two, one could will contrary to the other, and absurdity would follow. A stipulation is to be granted, so long as it is coherent, otherwise any conclusion could be deduced from it. As to whether the definition of an absolutely complete being is coherent, it should be noted that perfections, in being both simple and positive, cannot contain any explicit or implicit contradiction, and so the stipulate is logically coherent.
Defense of P1: This is to say that the term “God” refers to some imagined, conceived, or real object. The atheist should agree that “God” refers to some object, even if the object is just something in the theist’s fancy.
Defense of P2: Since the antecedent of (P2) specifies a way in which object to which the term “God” refers would be incomplete, it follows of analytic necessity that the object named by “God” is not absolutely complete, i.e. God is not absolutely complete.

Defense of P3: To grant that there is an object which truly and completely possesses the divine essence is semantically equivalent to granting that that which everyone calls “God”, i.e. a perfect being, exists in reality.

Further notes:

  • In other words, it is asking whether the object to which “God” refers is a perfect being. If it is not a perfect being, then “God” means an absolutely complete being and does not refer to an absolutely complete being. There is an “incompleteness” inherent in this relationship, which means that if “God” fails to refer to that which is truly God, then we mean that God, a complete being, is not a complete being. Our sense of “God” would be contradictory in nature.
  • We cannot include in the sense of what “God” is, the notion that “God” refers to something that isn’t completely God.
  • The only consistent alternative is to mean that the object which we name “God” exists in reality, and completely has the divine essence.
  • What Bonaventure is saying is that the sense of “God” must include that it references God, or else the the sense is incoherent. So to grant that there is an object to which the sense of “God” refers is sufficient to prove there is God.



Cx ≝ x absolutely complete
Dx ≝ x truly and completely has the divine essence
Rxy ≝ x is the entity to which “y” refers
E!x ≝ x exists in reality
g ≝ (ɿx)Cx

1. (∃x)Rxg (premise)
2. (∀x)[(Rxg ∧ ~Dx) → ~Cg] (premise)
3. (∃x)(Rxg ∧ Dx) → E!g (premise)
4. Rμg (1 EI)
5. Rμg ∧ ~Dμ (IP)
6. (Rμg ∧ ~Dμ) → ~Cg (2 UI)
7. ~Cg (5,6 MP)
8. (∃x)[Cx ∧ (∀y){[Cy →(y = x)] ∧ ~Cx} (7 theory of descriptions)
9. [Cν ∧ (∀y){[Cy →(y = ν)] ∧ ~Cν (8 EI)
10. [(∀y){[Cy →(y = ν) ∧ Cν] ∧ ~Cν (9 Comm)
11. (∀y){[Cy →(y = ν) ∧ [Cν ∧ ~Cν] (10 Assoc)
12. Cν ∧ ~Cν (11 Simp)
14. ~(Rμg ∧ ~Dμ) (5-13 IP)
15. ~Rμg ∨ ~~Dμ (14 DeM)
16. ~~Rμg (4 DN)
17. ~~Dμ (15,16 DS)
18. Dμ (17 DN)
19. Rμg ∧ Dμ (4,18 Conj)
20 (∃x)(Rxg ∧ Dx) (19 EG)
21. E!g (3,20 MP)



Noone, Tim and Houser, R. E., “Saint Bonaventure”, The Stanford Encyclopedia of Philosophy (Winter 2014 Edition), Edward N. Zalta (ed.), URL = <https://plato.stanford.edu/archives/win2014/entries/bonaventure/&gt;.

Seifert, Josef, 1992. “‘Si Deus est Deus, Deus est’: Reflections on St. Bonaventure’s Interpretation of St. Anselm’s Ontological Argument,” Franciscan Studies, 52: 215–231.

Posted on July 20, 2019, in Arguments for God and tagged , . Bookmark the permalink. 1 Comment.

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