Christopher Martin on Aquinas' Fifth Way

Christopher Martin provides an interpretation of the fifth way which I find rather plausible. He contends that “unconscious teleology is always relative to a system, is always a case of a part being for the sake of the whole” (1997, 200). Furthermore, he argues that if A is for the sake of B, and B is for the sake of C, but C is for nothing whatsoever, then A and B are also (in reality, initial appearances notwithstanding) for nothing whatsoever. As Martin puts it:

If l put my file on the floor, and then a book on top of it, and then my word-processor on top of the book, and then a flower-vase on top of the word-processor, and then put a stick in the flower vase, and then carefully wrap a small scrap of ribbon around the stick, a question arises of what the devil I'm up to; more scientifically, what is the point of all that? [...] If the last step of tying the ribbon, or the system as a whole, fails to have a point, one is surely entitled to say that the apparent point of each previous stage is wholly illusory. (Ibid., 196-197)

The fifth way then goes as follows: every instance of unconscious teleology is system-relative; the world is the all-encompassing system which includes all unconscious teleology. If the unconscious parts of the world are to have teleology, the world itself must have teleology (see Martin’s point above). “If the world has a point, if it is for anything, this cannot be a case of unconscious teleology, since unconscious teleology is always relative to a system, is always a case of a part being for the sake of the whole. There is, by definition, no greater whole of which the world forms a part. [...] Therefore the teleology of the world must be conscious: the point of the world must be conferred on it by some mind. ‘Therefore there is some being with understanding which directs all things to their end, and this, we say, is God.’” (ibid., 200). I think this is pretty convincing.

The Prior Probabilities of Theism and Naturalism

According to (what I think is) the right theory of intrinsic probability, there are three primary criteria which determine the prior of any given hypothesis:

1. Modesty: How little a hypothesis says about the world. 
• Example: "There is a living thing in my room" is a more modest claim than "there is a human being in my room," which in turn is more modest than "Richard Swinburne is in my room." More modest theories have more possible ways of being true: "There is a living thing in my room" could be true in any number of ways, "There is a human being in my room" in fewer ways, "Richard Swinburne is in my room" in only one way. Thus, more modest theories get a higher prior probability.
2. Coherence: How well the parts of a theory fit together, raising (or at least not lowering) one another's conditional probabilities.
• Example: "All Asian ravens are black and all non-Asian ravens are black" is a more coherent hypothesis than "All Asian ravens are black and all non-Asian ravens are white." (This is Draper's example.) Finding out that all Asian ravens are black increases the conditional probability that all of the non-Asian ravens are black, and vice versa. However, finding out that all Asian ravens are black reduces the conditional probability that all of the non-Asian ravens are white, and vice versa. So the parts of the first hypothesis raise one another's probability, while the parts of the second theory reduce one another's probability.
3. Brute limitations: Theories with arbitrary, inexplicable limitations should receive a lower prior than theories which lacks such limitations.
• Example: Consider two possible worlds, n and m. World n consists of a single particle moving at a constant finite velocity, while world m consists of a single particle moving at a constant infinite velocity. These two worlds seem to be equally modest and coherent: they both posit a single substance, behaving in a simple, uniform manner. Yet world m seems (to me at least) to be more intrinsically probable than world n. Why is this? The answer, I think, is that world n contains a brute limitation: why is the particle moving at the particular finite velocity that it is? Why not slightly faster, or slightly slower? World m, by contrast, has no such arbitrary limits. As such, it has a higher intrinsic probability.

(Note that this theory is largely a combination of Draper 2016 and Poston 2020.) It seems that if these three criteria are correct, then theism will always have an advantage over naturalism in terms of prior probability. The reason is this: the naturalist has to choose between coherence and a lack of brute limitations, whereas the theist can have both. Consider: if naturalism is true, then either every possible universe exists (i.e. there is something like a Lewisian multiverse), or else not. If not (i.e. if only one or some possible universes are realized), then the naturalist's theory will suffer from serious brute limitations. Why are these particular laws and physical structures instantiated, instead of all the other conceivable laws and physical structures which there could have been? Alternatively, if there is a Lewisian multiverse, then the naturalist's theory will avoid arbitrary limits, but only at the cost of an extreme lack of coherence (the Lewisian multiverse is just about the least uniform way that reality could conceivably be).

The upshot is that the naturalist faces an inevitable trade-off between coherence and a lack of brute limitations. The theist, however, faces no such difficulty: theism is both a highly coherent hypothesis (it posits a being with all possible perfections, which is a very uniform array of properties), and it is largely lacking in brute limitations (since God's properties are infinite). If all of this is correct, then it seems as though theism should get a relatively high prior as compared to naturalism.

Why Would God Make a Complex Universe?

While perusing Alexander Pruss' blog, I came across a post in which he offers this quote from Aquinas:

Hence we must say that the distinction and multitude of things come from the intention of the first agent, who is God. For He brought things into being in order that His goodness might be communicated to creatures, and be represented by them; and because His goodness could not be adequately represented by one creature alone, He produced many and diverse creatures, that what was wanting to one in the representation of the divine goodness might be supplied by another. For goodness, which in God is simple and uniform, in creatures is manifold and divided and hence the whole universe together participates the divine goodness more perfectly, and represents it better than any single creature whatever. (ST 1.47.1)

It occurs to me that this line of thinking could be used to support Swinburne's inductive cosmological argument, which goes like so: let "h" be theism, "e" be the existence of our universe, and "k" be our background knowledge (which in this case will consist only of logically-necessary truths). Since the physical universe is extremely complex, it is a priori very improbable that it should exist. However, Swinburne claims that God would have very good reason to produce such a universe, since he would be motivated to create embodied rational creatures, and such creatures would need a universe to live in. So P(e|h&k) is relatively high, while P(e|~h&k) is very low. Hence, P(h|e&k) > P(h|k).

Aquinas' aforementioned reasoning can, it seems to me, be used to substantially strengthen this argument. It does so by explaining why God would want to make a complex universe (such as we observe) rather than a very simple one, suited simply to the purpose of playing host to embodied rational agents. If all goodness involves participation in God (which it does), then (as Aquinas notes) the particular perfections of each individual type of creature can model the divine goodness in unique ways. This plausibly gives God good reason to make a varied and complex universe. This in turn raises P(e|h&k), thus strengthening the argument.