Suffice it to say, if you're familiar with my blog, you'll know that I find natural theology to be a failure. I'm pretty dedicated to showing exactly how and why such arguments are false.
However, on thinking about the topic last night I was struck by a line of argument I've had on the periphery for a while.
Consider the definition of natural theology: "Natural theology is a program of inquiry into the existence and attributes of God without referring or appealing to any divine revelation."
Lets assume for a moment that if natural theology actually worked, that it was gods intention that it work. So it's not say, incidental to Christian theism being true.
Next, consider the direct implications of Christian focused natural theology: There is a god, and this god wants you to believe he both exists and has a specific set of properties. This god wants you to be a Christian. More specifically wants there to be evidence for his existence, and for belief in him to be achievable through reason.
Lets also consider a less direct implication of being a Christian: This god wants you to believe the bible is his divinely inspired word which is, liberally interpreted, "true in all things it teaches".
If god's goal in "leaving the breadcrumbs in creation" for natural theology to work was to leave a path for humans to eventually believe in him to come to a relationship with him, then natural theology is a particularly poor way to go about this.
There is very little in the way of natural theology in the bible. What happens when god wants to get someone's attention he performs miracles, and not just any kind of miracle. Generally we're talking about dramatic violations in the laws of physics/biology/chemistry.
Assuming the bible is accurate, when Jesus wanted to demonstrate to his apostles that he really was the messiah, he didn't, per Swinburne, engage in a very lengthy a priori metaphysical dissertation about how the necessary ground of all being must exist in a trinity that must redeem mankind from its own sinful nature.
No! He rose himself from the dead. He healed the sick. Walked on water. Multiplied food a thousandfold. Raised other people from the dead.
When Yahweh wanted to demonstrate his primacy over the false god Baal, Elijah didn't engage in apologetics. He called on Yahweh to rain fire from heaven to consume a water logged dead bull!
The list of examples I could give here is pretty extensive, but I think you get the idea.
As such I propose another principle I think Christians would have to agree with: When it comes to convincing people of his existence, let alone the specific truth of Christian theology, miracles are a far more effective tool than apologetics and natural theology.
Miracles don't happen these days
To be fair, I'm talking about a very specific type of miracle here. I'm talking about the kinds of dramatic miracles we have tons of examples of in the Bible. I'm not talking about the kinds of "miracles" you'll hear a subset of apologists defend today: the kind where some unlikely, but wholly explainable via naturalistic methods event occurs. Here's a good example of what I don't mean by miracle.
I'm talking about the kinds of dramatic miracle we see copious examples of in scripture: Walking through walls. Regrowing limbs. Raising people from the dead. Etc.
These miracles weren't just one off instances either. In many cases, the same person could perform multiple signs in the name of Yahweh. It was demonstrable and repeatable, which was absolutely key for proving that a prophet was of god, or in Jesus's case, was god.
What's worse for the theist is that in many cases where miracles are purported to have occurred and they can be investigated, they invariably show that no such miracle occurred.
If the purpose and intention of natural theology is to lead people to belief in god and more specifically a certain religion through evidence and reason - then even Christians will have to admit that it is a particularly poor way to accomplish that goal compared to other ways god has supposedly achieved that same goal in the past.
This seems to reflect poorly on theists, but how is it self defeating?
Well if god wants believers, but is no longer willing to use dramatic, laws of nature defying miracles to achieve that goal, then he must have some very specific, morally sufficient reason for relying on natural theology in modern times.
This means god is intentionally using a far less effective method to achieve his desired outcome.
If that's true, then god wants you to believe in him, and to have good reasons to believe in him, yet he won't give you the "best kinds" of reasons to believe. God supposedly wants to impose a significantly higher barrier to belief in him now than has existed in the past.
Why would an all loving god privilege the epistemic status of a tiny fraction of prehistoric and first century Jews over the rest of the species?
Theists will struggle to deny this
It is very hard for a theist to deny that belief in god now is significantly harder to achieve than it was in the time when Jesus and the apostles were regularly performing miracles.
To deny this is to say that the same number or less people would believe in, and refuse a loving relationship with god than if we had repeatable demonstrable miracles from Christians.
Can you imagine that being possible? I know I would believe in and accept the divine command theory of ethics if say only Catholic priests in good standing could actually perform the miracle of transubstantiation, outside of the body. That is they would transform bread and wine into the literal flesh and blood of Jesus Christ.
Imagine that! Imagine Catholic priests could do this in the intervening centuries since Jesus purportedly lived. No other religious adherents could do similar miracles. Imagine that as science progressed, we were able to see that all around the world the flesh and blood these priests miraculously transubstantiated had the exact same DNA! Imagine this could be done given every controlled experiment we could ever perform.
How many more people would convert to the Catholic faith if this were possible? Would apologists avoid pointing to this demonstrable and repeatable miracle when trying to convince others about the truth of Christianity? I sincerely doubt it!
One can't say that no one would have the option to rationally deny Christianity at that point. As I've written before, one can very easily add in the assumptions necessary to logically hold that such miracles aren't actually miracles. It's certainly much harder to deny, but it's not rationally impossible to do so, unless theists want to say that those who deny the external world are not rational (which would cause all sorts of conflicts with Plantinga's reformed epistemology).
The contentious nature of Natural Theology
In reality, even apologists will admit that there are responses, counter-responses, counter-counter-responses and so on to the arguments from natural theology. One point I hope to make in this new year is that if we start from the least amount of assumptions, natural theology will be unconvincing. That's a post for another time however. For now, the point is that natural theology is fraught with problems, yet is is one of the primary ways apologists try to get people to believe in god.
What's worse is their fall back position, that of subjective personal revelation. This is a method of knowing that is demonstrably unreliable for religious truths (if there are any), since all religious believers of contradictory religions all point to subjective personal experience to justify their beliefs.
In fact, when pressed on this point, apologists will quickly start talking about the ministerial use of reason rather than the magisterial use of reason. That is, they will argue it's arrogant to say a human can be justified in not believing in god because they never heard any good arguments to believe.
Yet at the same time very few actual theologians and philosophers of religion will say that atheism is irrational. That tends to the ground occupied by amateur hack apologists online.
So what's left is that god wants you to believe, for good reason, but not for reasons so good that it becomes harder to deny his existence than to affirm it. I hope to have shown that this is a consequence of the beliefs that natural theology will lead you to if you become a Christian. For this reason, I think at least Christian natural theology is self defeating.