This is part of a series of posts in response to "Letters to a Doubting Thomas" C. Stephen Layman.
For the first post, I'd like to lay out Layman's groundwork first chapter. In the book, Zach (the philosopher theist) receives a letter from his long lost college friend, Thomas (the agnostic). In the first chapter, Layman presents some recurring themes that will come back up throughout the book. For example, here is his definition of theism:
Theism: (1) There is exactly one entity that is (2) perfectly morally good and (3) almighty and that (4) exists of necessity.
Conversely, he defines naturalism thusly:
Naturalism: (1) There is a self-organizing physical reality (i.e., there is a physical reality whose nature is not imposed by a god or by any other force or agent), (2) physical reality exists either necessarily, eternally, or by chance, and (3) leaving aside possible special cases (see later), all entities are physical entities.
The reason to lay out both hypotheses is that Layman states that one can only compare apples to apples. One can't simply compare theism to ~theism; one needs to compare theism, a positive argument for how the world is, to another competing set of positive claims for how the world is. This is the first mistake in the book, in my opinion. One doesn't need a comprehensive explanation for all the various items Layman is going to attempt to explain with theism in order to evaluate whether or not theism does a good job. It isn't intrinsically about theism or naturalism; it's about theism vs. ~theism.
Zach also lays out some criteria for background knowledge (logic, common sense, etc.) as well as the "principle of simplicity" for Thomas as terms for establishing the advantage of one explanation over another for the future discussion. The criteria for simplicity are (my mini-explanations in parentheses):
1. The number of things postulated (less is better)
2. The number of kinds of things postulated (less is better)
3. The simplicity of the terms (this is to avoid hiding complexity in words; the definition of the words and resultant complexity derived from the definition must also be taken into consideration)
4. The number of statements within a hypothesis that receive little or no probabilistic support from other statements contained in the hypothesis (the more terms contained in an explanation, the more likely it is to be false)
Thomas accepts the terms and immediately recognizes that theism seems, a priori more complex than naturalism due to positing more things (not only a univers, but another entity), more kinds of things (natural and spiritual things), more complicated terms (like omniscience and omnipotence), and more claims in general (he points to Zach's definitions as containing 4 terms under theism and only 3 under naturalism). Zach, somewhat surprisingly, accepts Thomas' observations:
I end where I began, agreeing with your claim that Naturalism is a significantly simpler hypothesis than Theism.
The chapter ends with a discussion about how naturalism might be self-defeating. Layman refers to the work of Plantinga on this:
Plantinga's basic idea is that, from the standpoint of Naturalism, the origin of our cognitive faculties gives us a reason to doubt their reliability. Given Naturalism, our cognitive faculties evolved without God (or anyone else) overseeing their development. Only the "blind" forces of nature were at work, e.g., random genetic mutation and natural selection...
From an evolutionary standpoint, the human brain and nervous system enable us to behave in ways that promote survival and reproduction. In other words, from the standpoint of evolution, it is behavior that matters, not beliefs. So it seems possible that humans might be successful at survival while having mostly false beliefs (and, hence, unreliable cognitive faculties).
Here's the question we have to ask: How likely is it that our human cognitive faculties are reliable, assuming that Naturalism is true (and that our cognitive faculties evolved without guidance from any intelligent being)? Plantinga argues that the probability is low or beyond knowing; and either way, Naturalism leads us to doubt the reliability of our cognitive faculties. But, as noted earlier, Naturalists themselves believe that our human cognitive faculties are reliable. Thus, Naturalism is self-defeating.
Thomas is a bit skeptical of how we might have evolved with false beliefs, and Zach responds with some more material from Plantinga, who states that ancient man could have believed a tiger was cuddly but thought the best way to run toward it was actually running away, or that he wanted to go to the tiger but also wanted to lose weight and so ran away at top speed, or runs away because he doesn't think the tiger will see him despite him wanting to be eaten. The point is that someone could believe wrongly while still surviving.
While these are somewhat "cute" examples, they seem to complicate the matter. This sword is actually going to cut two ways. Layman wants the function of "belief" to seem "too good to be true," and thus point to an intelligent creator who gave us such a faculty. The first cut of the sword is that it's not self-evident that it would be evolutionarily advantageous or equivalent to have things not turn out like they did. Could these examples above really have provided equivalent survival mechanisms? These are just snapshots of one way a belief could have been different. But beliefs are more like a web or heuristic in these cases than a rolodex of individually targeted cause/effect notecards. Thus, the above examples seem fairly ad hoc to me. It over-complicates things to come up with a system of beliefs that might have been false while still surviving.
On that note, however, we have the other side of the sword. Let's grant that an omnipotent, omniscient being provided us with "true belief" faculties that let us exercise this fantastic ability and "believe rightly." Cognitive science shows us that we don't. The faculty isn't nearly as great as we'd like to believe. Man is not rational and believes wrongly all the time. We're filled with biases and false arguments. Thus, even giving Layman what he wants, an admission that belief is just too accurate about reality to have happened by chance, does't fit his purposes of pointing to god has having implanted it. Instead, we have something more fitting of evolutionary biology. We really do have a hybrid -- beliefs that track well enough for survival, but ones that aren't tracking as we get better and better at improving our maps of the territory around us.
In any case, this example doesn't carry very far in the book. The chapter primarily sets about to establish some definitions and the principle of simplicity. The next chapter examines why Zach things theism is still worth looking at.