Dr. Graham Oppy on the Nature of Arguments (With Existential Inertia as Bonus) | (MoR No. 4)

In this episode, I chat with Dr. Graham Oppy, professor of philosophy at Monash University, about the nature, purpose, and conditions of success for arguments. We also talk about Feser's Aristotelian proof and existential inertia. Those who wish to pursue these matters further can read "The Normative Status of Logic" (SEP).

~

I have a number of corrections and clarifications to make for what I said between 1:45:45 and 1:47:03.  

First, I am simply reporting what seems to me to be Feser's attitude toward his premises. I do not claim this is the only possible or rational interpretation of Feser's level of confidence or certainty. I cannot know Feser's own doxastic states, and I want to renounce any psychologizing of his doxastic states that I may have implied in what I said in this clip.

Second, there is evidence for my claims about Feser's thinking his premises are demonstrably certain. At the end of his Five Proofs, Feser writes:

"A third problem with [an objection previously considered] is that those who raise it often misunderstand what classical theists like Aquinas mean when they say that God’s existence can be “demonstrated”. What is meant is that the conclusion that God exists follows with necessity or deductive validity from premises that are certain*, where the certainty of the premises can in turn be *shown via metaphysical analysis*. That entails that such a demonstration gives us knowledge that is more secure than what any scientific inference can give us (as “science” is generally understood today), in two respects. First, the inference is not a merely probabilistic one, nor an “argument to the best explanation” which appeals to considerations like parsimony, fit with existing background theory, and so forth, but where some alternative explanation might in principle be correct. Again, it is instead an attempt at a strict deduction to what follows necessarily from the premises.

[...]  

[T]he argument can successfully be defended against *all objections claiming to show that the conclusion does not really follow or *that the premises are doubtful*. Now, that has been accomplished in this book with respect to the proofs just mentioned, from all of which it follows that God exists." (p. 307) [Emphasis mine]

This shows rather forcefully Feser's attitude towards his arguments, and -- at the very least -- my interpretation in the clip is not an uncharitable one. Feser then ends his book with the following:  

"Quod erat demonstrandum." (p. 307)  

Denotatively, this means 'that which was to be shown'. In fact, however, the connotation is extremely strong, often connoting a decisive proof or demonstration of something. Traditionally, it's placed at the end of formal mathematical proofs whose conclusions follow from indubitable premises and axioms. Its use in philosophy also traditionally signifies an indubitable, certain, demonstrable proof. Consider, for instance, Spinoza's Ethics (1677). Spinoza frequently used it at the end of his philosophical arguments in such a book. It's no coincidence, moreover, that the style and system of the book are, as Spinoza says, "demonstrated in geometrical order", with axioms and definitions followed by propositions.

Third, regarding the 'real debate' quote. Here is Feser's full quote:

"That is a confident claim, I realize. But natural theology, historically, was a confident discipline. A long fine of thinkers from the beginnings of Western thought down to the present day... have affirmed that God’s existence can be rationally demonstrated by purely philosophical arguments. The aim of this book is to show that they were right, that what long was the mainstream