You can't use philosophy to demonstrate that God exists

Over the years in writing this blog, William Lane Craig has provided plenty of cannon fodder for me; more recently, Randal Rauser has proved to be a wellspring of facepalm-worthy apologetics and pseudoscience. Both have one thing in common: they're both philosophers by trade who think that it's possible to prove the existence of God through the use of deductive logical arguments.

Here's a quote, for example, from Randal's latest post, which is itself a quote of another apologist-philosopher type, Edward Feser:
In each case we have [apologetic] arguments to the effect that the material universe in principle must have had a cause and that the divine cause arrived at not only happens not to have a cause (as a “brute fact” would) but rather in principle could not have had or needed a cause and in principle could not have not existed.  And the reasons, of course, have to do with the metaphysics of potency and act, the difference between composite substances and that which is metaphysically absolutely simple, the real distinction between essence and existence in anything contingent, and other aspects of classical metaphysics in the Aristotelian, Neo-Platonic, and Scholastic traditions.
All of this quasi-academic blather rests upon the misguided notion that it's even possible to establish knowledge about the external world (its properties, origin, causes, etc.) without actually going out there and looking at it. It's not an empirical endeavor that relies on observation, but one that relies on a priori "truths" in the Rationalist vein of Rene Descartes.

The Kalam Cosmological Argument is a fine example. William Lane Craig says that the basis for the first premise ("Everything that begins to exist has a cause for its existence") is based on "the metaphysical intuition that something can't come from nothing". Wait... "metaphysical intuition"? Let's look at that more carefully. When asked to expound on that point in both his debates and his written work, Craig usually goes on to point out that this is consistent with what we observe – that we don't see things just "popping into existence", so to speak. We always observe things coming into existence as the outcome of prior causes.

The problem is, that is an empirical observation. What Craig then does is treat that observation as an a priori truth – it's not just something we observe in our day-to-day reality, but something that is always true in every conceivable circumstance. The entire Kalam is therefore undermined with the most basic retort to its first premise: maybe not.  Now, personally, I would argue (and have argued) that classical concepts of logic and especially causality are nonsensical when trying to describe quantum mechanics. No philosopher could have ever describe the double-slit experiment through a priori reasoning. But even if I didn't have quantum mechanics on my side – if I had been living in antiquity, for example – I still could have rejected such a premise on principle alone. How does Craig know that all things in all conceivable circumstances behave according to the same rules and laws he observes in his immediate frame of reference? If that seems a little narrow-minded, that's because it is.

I've seen this objection to the Kalam put much more simply: just because things within the universe are subject to causality does not mean that the universe itself must be subject to causality. There are two reasons for thinking that this case has not been established. The first is that we don't know what it's like to measure the universe as a set. How could we? How could we step "outside the universe" and make empirical observations? The second is that it's arguably nonsensical to even talk about something like causality without the context of the physical universe. Every observation of what causality is – and that includes Aristotle's "Four Causes" all the way to a more modern Newtonian scientific definition – has been inferred from observation of the physical universe. If we strip the universe away, why should we assume the rules still apply? What does it mean to talk about causality without time, space, matter or energy?

When confronted on this in an old Q&A, Craig retreated to the old "prove it's impossible" canard. But we're not the ones asserting the first premise of the Kalam as an a priori truth, and the burden is on him to demonstrate it as so. Unfortunately for Craig, he simply can't, because that would require something theists are fond of accusing atheists of flouting – knowledge of everything.

Possible objection 1: "Scientists do that all the time!"

Here's a predictable objection: Scientists do that all the time! If you don't acknowledge certain a priori truths, you can never do any experiments in the first place!

This objection (or some variation of it) is one that I've heard innumerable times from theists over the years on this blog and elsewhere on the theological underbelly of the interwebs. But it's conflating two very different things: a priori knowledge and provisional assumptions.

A fine example is the ubiquity of physical laws: scientists assume that the laws of physics are the same everywhere in the universe. But unlike a priori truths, scientists know that you can't actually learn anything about the universe with a provisional assumption; rather, it's more like a starting point to spearhead further empirical inquiry – and it's an assumption that, by natural of being provisional, could be wrong. No scientist would be caught dead using an argument like this:
  • The law of gravity holds within the currently observable universe
  • The laws of physics are the same in all parts of the universe
  • Ergo, the law of gravity holds beyond the currently observable universe
It's entirely possible – although improbable – that we could indeed someday observe a region of deep space in which the law of gravity does not hold.  We do not mistake our empirical observations for immutable truths – and yet that is exactly what Craig and those of his ilk do when they cantilever a priori truths into realms that are either untested or even untestable. How can Craig possible know that "everything that begins to exist has a cause"? He can't, of course, because he's making the mistake of deriving an a priori "truth" from an empirical observation.

Possible objection 2: "It's like math!"

I've seen mathematics brought up on more than one occasion as an example of something that supposedly allows us to learn about the world through reason alone. After all, so the theists say, you can't prove the foundations of mathematics are true; you just have to acknowledge them as a priori truths in order to learn anything about the world at all! But the foundation of mathematics, which is called "set theory", is indeed based on empirical observation: the observation of discrete objects that can be grouped into sets. From that, we can abstract arithmetic, irrational numbers, and various theorems and complex mathematical axioms.

However, all mathematics can do is tell us the consequences of axioms. It can't tell us which of those axioms actually correspond to reality! If that were possible, then physicists wouldn't bother doing experiments; they'd simply "math" their way to the secrets of the universe. But physicists do experiments because it's impossible to know, just by mathematics alone, what the universe is actually like. It's entirely possible for us to create mathematical structures that have absolutely no referent in physical reality whatsoever, and/or to create ones that are contradictory to each such that either might exist, but both could not. That's why, just like with anything else, learning anything about the world through math requires observation and experiment.

Possible objection 3: "It's properly basic!"

This is a lot like the first objection, in that the assumption is that we have to hold certain things as true in order to make sense of anything else. But in this case, we might take the process all the way down to our basic perception of the world and our subjective experience: i.e., "rational intuition". But the problem for a priori knowledge again rears its ugly head. We can't know that we're not plugged into a Martix-like simulation, or that we're not a manifestation of another creature's dream, or that we weren't created moments ago with the illusion of memory; instead, we simply acknowledge that there's no justification for assuming such things to be true. Not unlike the ubiquity of physical laws, we can take the basic axioms of rational intuition, such as "I exist" and "My sensory experience is generally reliable", as provisional assumptions that are a starting point to further inquiry rather than immutable truths.

One theist offered this retort:
I say the knowledge of efficient-final causality is embedded in our mind by nature, and we know it a priori.
Oh... he says! Well golly, I'm convinced! Look, this is like saying that you know God exists because God gave you the knowledge that he exists. It relieves your position of epistemic humility and begs the question at the same time! The fact that some theists fail so completely to recognize such flagrantly circular reasoning shows just how ridiculous the whole charade really is.

There's a trend I'm seeing more and more frequently in which theists trot out all sorts of obscure philosophical arguments for God's existence. Each one has umpteen different forms, so if you take the time to refute one of them, the theist can just come back with "Oh, but that's not the version of the argument I agree with," or some such nonsense. We can avoid a lot of useless discourse if we really start hammering these Christian-philosopher types with a basic fact: you cannot prove or disprove the existence of God with logical argumentation.

Logical axioms give us a framework for understanding the world around us – not a basis for inferring immutable truths. When we point this out, theists have no choice but to retreat to the idea that belief in God is just a matter of faith. I mean obviously, we don't sit around arguing about whether the sun or the moon or you or I merely exist (well... anti-realists not withstanding...). That's because there's evidence – such overwhelming evidence, in fact, that it's easy to take it for granted. The evidence that God exists? It's right there, as long as you're content to worship the sun.


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