Agnosticism Makes Knowledge Impossible

In chapter seven of Warranted Christian Belief, Alvin Plantinga discusses the epistemological implications of agnosticism - specifically David Hume's formulation of it.

I shall argue that one who displays a certain kind of agnosticism with respect to his origin and place in the universe, and also grasps a certain cogent argument, will not, in fact, know anything at all; nothing he believes will have warrant sufficient for knowledge (218).

Plantinga then reminds us that a skeptical position does not know where we have gotten our faculties from. He reminds us that when it comes to where the universe came from, Hume declares, "A total suspense of judgment is here our only reasonable resource." Not only does the agnostic not know where our faculties came from, but he does not know the exact purpose which they were designed to serve.

Given agnosticism, our cognitive faculties could have come from any number of logically possible sources:

• We might have been created by God.
• We might have arisen from vegetative principle.
• We might have arise from copulation on the part of animals we know not of.
• The list of possibilities goes on and on.

In some of these possibilities, we would have warrant for believing our faculties to be reliable, but not in all of them. Given agnosticism, we do not have epistemological grounds for discerning which possibility is legitimate and which is not. As such, Plantinga says that the probability of our faculties actually being reliable is inscrutable - or unknowable. Here is how he expresses it:

R = The Proposition that our cognitive faculties are reliable
F = The relevant facts about our faculties' origin, purpose, and provenance
P = Probability

P(R/F) is unknowable. "Another way to put it: the probability of R given Hume's agnosticism is inscrutable." Plantinga uses a story to illustrate. He suggests a scenario where our space ship lands on a distant planet and upon cracking upon the door of the spaceship we find a radio that is telling us things that we have no knowledge of (what the weather in Beijing is, whether Caesar had eggs on toast on the morning he crossed the Rubicon, whether the first human to cross the Bering Strait into North America was right or left handed, and so on). Plantinga reminds us that although this device is spitting out information, we have no grounds for believing its statements to be factual because we do not know what its purpose is, or whether it has a purpose. "You see that the probability of its being reliable, given what you know about it, is for you inscrutable."

The fact that we do not know what the device's purpose is, or whether it has a purpose is the defeater for the proposition that the device speaks the truth. We are not warranted in believing what the device is telling us, given this defeater. Plantinga then applies this to agnosticism.

Because B is just any belief I hold - because I have a defeater for just any belief I hold - I also have a defeater for my belief that I have a defeater for B. This universal, all-purpose defeater provided by my agnosticism is also a defeater for itself, a self-defeating defeater...Thus the true skeptic will be skeptical all the way down; he "will be diffident of his philosophical doubts, as well as his philosophical conviction" (226)

Skepticism is self-defeating. It is the undefeatable defeater. "That is because any doubt about our cognitive faculties generally is a doubt about the specific faculty that produces this conviction."

Even if our apologetic methodology differs from Plantinga's, even if we disagree with his arguments in God Freedom and Evil, this is a very strong argument, and one which we Van Tillians should be quick to utilize. This argument is very similar to Plantinga's argument that naturalism is self-defeating, and I plan on taking up that argument as well at some point in the future.