As a Christian, I believe that “God is a knower, and indeed the supreme knower… We human beings, therefore, being created in his image, can also know much about our world, ourselves, and God himself.” As such, when I attempt to think clearly I suppose that I reflect God’s character as a rational being.
What about the skeptic? Previously I discussed how the combined belief in naturalism and evolution undermines itself. If they are both true, then one has a reason to doubt the reliability of one’s cognitive faculties. If that is so, then one must doubt every belief that one holds, including the belief in naturalism and evolution.
A similar argument can be made addressing agnostics in particular. Alvin Plantinga also argues that “agnosticism with respect to origins destroys knowledge.” If his argument is cogent, then the agnostic finds themselves in an awkward position—especially if they claim to inhabit the “reasonable camp” within the “God” discussion. Those who regard theism to be intrinsically unreasonable or irrational ought to take note. Tu quoque.
Let’s get started. Suppose that one abandons the view “that we have been created by a benevolent deity.” According to Plantinga, this should lead to an “existential crisis.” How does merely not believing in God get one into such a crisis? Consider the following example.
Suppose you travel to a different planet as part of an interstellar expedition. On arrival, you discover a box that looks something like a radio. This box periodically broadcasts sounds that turn out to be English sentences. These sentences offer seemingly random facts about things of which you have no knowledge.
For example, it tells you “whether Caeser had eggs on toast on the morning he crossed the Rubicon, whether the first human being to cross the Bering Strait and set foot on North America was left-handed, and the like.” You may be initially impressed and believe the alien box. Indeed, how else could you discover such facts?
But then a doubt enters your mind, “you recall that you have no idea at all what the purpose of this apparent instrument is, whether it has a purpose, or how it came to be. You see that the probability of it being reliable, given what you know about it, is for you inscrutable.”
The reasonable thing to do is withhold belief about whether the alien box speaks the truth. Without knowledge of its purpose and origin, one cannot trust it. One must neither believe nor disbelieve the facts offered by the alien box.
The agnostic faces a similar situation regarding their own cognitive faculties. Agnosticism towards God leads to agnosticism about the origin of one’s cognitive faculties (unless you positively believe naturalism and evolution, but that’s another story).
But if one is agnostic about the origin of one’s cognitive faculties, then there is little reason to think that they are reliable guides to truth. Since all beliefs are the fruit of one’s cognitive faculties, one must also be agnostic about all one’s beliefs.
Agnosticism thereby leads to “complex, confusing, multilayered, reflexive … skepticism in which I am skeptical of my beliefs and also of my doubts, and of the beliefs that lead to those doubts, and of my doubts with respect to those doubts, and the beliefs leading to them. Thus the true skeptic will be skeptical all the way down.”
Of course very few of us actually feel this way. What does that prove? Not much. If a man is accused of being a liar, we can’t just ask him whether or not he is in fact a liar. Similarly, I can’t claim the Bible is true just because it says so. The same standard applies to one’s cognitive faculties—they can’t vouch for themselves when they themselves are on trial.
One needs an epistemic anchor outside of oneself to avoid this bottomless skepticism. Theism offers such an anchor; atheism and agnosticism do not (for different reasons).
Prior to being appraised of this argument, however, the agnostic may indeed have knowledge of the world, themselves, etc. After all, on theism even the agnostic is made in God’s image and does in fact have reliable cognitive faculties.
However, once appraised of this argument—and unable to avoid deep skepticism—the agnostic will lose their knowledge. This is a strange situation where “by learning more, one comes to know less.” Simply claiming to be rational won’t do. The agnostic must face the fact that they cannot justify trusting their own thought processes.
 Alvin Plantinga, Where the Conflict Really Lies: Science, Religion, and Naturalism (New York, NY: Oxford University Press, 2011), 268.
 Alvin Plantinga, Warranted Christian Belief (New York, NY: Oxford University Press, 2000), 227.
 Ibid., 222.
 Ibid., 224–225.
 Ibid., 224.
 Ibid., 226 emphasis added.