|Evolutionary Argument Against Naturalism|
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The ANPD Scenario
It would seem to be the case that Pr(R|N&E&SE) is low, but what if SE were false? What if in spite of Plantinga’s Argument Against Materialism, one is still convinced that the semantic content of a belief is causally relevant on naturalism? In that case there’s another thought experiment I’ll call the “ANPD scenario.”
Suppose a mad scientist creates an artificial neurophysiological device (ANPD), a many-tentacled device implanted near Smith’s brainstem that controls both his thoughts and behavior. The mad scientist can remotely control the ANPD’s electrochemical processes to vary Smith’s beliefs and behavior in innumerable and diverse ways. For example, Smith is dehydrated, and the mad scientist, wanting his victim to be in good health, uses the ANPD to force Smith to drink some water while simultaneously making him believe I am thirsty and this water will quench my thirst. The second time Smith is dehydrated, the mad scientist uses a different electrochemical setting to make Smith believe Drinking this water will grant me superpowers in the afterlife while producing the same drinking behavior (and suppose this belief is false). Here, the electrochemical process that produces fitness-enhancing behavior also produces a false belief. The ANPD can even produce “garbage” semantic beliefs that have little to do with the forced behavior, such as making Smith believe that Grass is air or that 1 + 1 = 3 at the same time it causes Smith to drink the water. The third time Smith is dehydrated the mad scientist configures the ANPD so that it causes Smith to drink the water while also causing him to believe Grass is air. Indeed, the mad scientist can associate just about any belief with the same drinking behavior.
For those who think that the semantic content just is neurophysiology and think that this avoids SE (it doesn’t, as I argue in the reductive and nonreductive materialism section in my article on Plantinga’s argument against materialism) let it be noted that the mad scientist can even use the device so that the physical properties of the belief Grass is air trigger an electrochemical reaction that causes Smith to drink the water, and this is possible because on naturalism it’s how a belief’s physical properties interact with the rest of the system that determines one’s behavior. So even if it were the semantic content of Grass is air that is causing the action here, the ANPD scenario would show that the semantic content need not cause behavior in a manner befitting a rational agent; the causal link could be akin to the effects of SE whereby the semantic content of the belief doesn’t even need to have anything to do with one’s external environment (thereby mimicking the effects of SE when SE says it’s the NP properties and not the semantic content that causes belief). To have some handy terminology, let’s say that semantic content is causally relevant in a meaningless way when it fits situations like the semantic content Grass is air causing one to drink water, and say that semantic content is causally relevant in a meaningful way the casual link is more apropos of a rational agent, such as when This water will quench my thirst is (part of) what causes me to drink water.
Such an artificial neurophysiological device is not only metaphysically possible, but it also seems to be physically possible (given that beliefs and behavior can be brought about by electrochemical means). The ANPD scenario shows that false beliefs can be associated with fitness-enhancing behavior, even to the point where the false beliefs are garbage beliefs (beliefs that are wildly unrelated to the external environment, as in dreams). But if the scenario’s artificial neurophysiology is physically possible, then it is at least metaphysically possible for an evolved creature’s natural neurophysiology to have the same “disconnect” between semantics and behavior. Even if were possible for a belief’s semantic content to be causally relevant, the ANPD scenario shows that for any given behavior B, there are innumerably many semantic contents C—even C’s wildly unrelated to the external environment—that could be associated with B. Like SE, this would still allow for the possibility for beliefs and behavior to be linked in a meaningful manner (e.g. I believe a plant is poisonous so I won’t eat it) but like SE, this also allows for the possibility of even garbage beliefs to be associated with advantageous behavior, and have belief/behavior disconnects identical in effect with SE even if SE were false, e.g. when the physical properties of Grass is air cause Smith to drink water, thereby mimicking the effects of SE when SE says it’s the NP properties and not the semantic content that is causally relevant. One could argue that the relation between semantic content and behavior is in this way functionally equivalent to SE in spite of the falsity of SE. Call this view semantic pseudo-epiphenomenalism (SPE).
Two key claims of SPE are (1) SE is false; (2) even though SE is false, it is still possible for even garbage beliefs to be associated with advantageous behavior (as by semantic content influencing behavior in a meaningless way)—and the ANPD scenario demonstrates that this is indeed physically possible (since the device is physically possible). The ANPD scenario thus shows that if SE isn’t true, then SPE is. Both SE and SPE permit a great divorce between beliefs and behavior (again think of the case where the belief Grass is air causes Smith to drink water). Upon reflection it’s very easy to envisage a set of moving atoms that create advantageous behavior while producing beliefs unrelated to the external world, and it’s easy to take for granted our rather fortunate truth-conducive relationship between belief and behavior because it is so familiar to us. Yet if naturalism were true and SE were false, semantic content being casually relevant in a meaningless way would be very possible.
To again avoid bias our own species, think not of us but of alien creatures on some other world where N&E&SPE holds for them. While it’s easy to assume that beliefs and behavior would be linked in a “rational” manner (e.g. a man believes water will quench his thirst so he drinks), there’s nothing on N&E&SE or N&E&SPE alone to believe such a link would occur for the aliens (whose physiology, we may presume, differs from ours), since both SE and SPE easily allow garbage beliefs to be connected with advantageous behavior. Because SPE is functionally equivalent to SE, and given the enormous variety of diverse beliefs that could be associated with a given behavior (e.g. Bachelors are married, Grass is air, 2 + 2 = 1, and 2 + 2 = 2) an evolving race of alien creatures afflicted with SPE has a low probability of evolving reliable cognitive faculties just as if they were afflicted with SE. In sum, naturalism entails that either SE or SPE is true, and since Pr(RA|N&E&SE) and Pr(RA|N&E&SPE) are low, it follows that Pr(RA|N&E) is likewise low. But then if Pr(RA|N&E) is low, then Pr(R|N&E) is also low (since, as with the case of the aliens, we are basically considering the likelihood of R on N&E without further relevant information).
In response one could put forth the following rebuttal. Even though naturalism unavoidably entails an SE-type problem—whether via semantic epiphenomenalism or semantic pseudo-epiphenomenalism—the fitness-enhancing neurophysiological properties that are most likely to be selected by natural selection (say that a certain neurophysiology is selectable if it’s likely to be selected by natural selection) happen to be those that are truth-conducive. The ANPD scenario, while physically possible, is contrived and produces certain belief-behavior pairs that are unlikely to obtain in real human physiology. The most selectable and efficient way for neurophysiology to produce advantageous behavior also produces mostly true beliefs. Thus, even though the SE-type situation exists for semantics and behavior, luckily for us the physiological relation between semantics and behavior is such that true beliefs usually obtain.
All that may be true, but as an objection against the Probability Thesis it falls short. A major problem is that even if a favorable physiological relation between beliefs and behavior obtains for our species, such a favorable relation does not appear to be knowable from N&E alone. It is not knowable from N&E&SE alone, nor is it knowable from N&E&SPE alone. To illustrate the problem, consider a planet with aliens whose neurophysiology radically differs from ours (though we don’t know much more about it). On N&E&SE where the semantic content of a belief is causally irrelevant, it would still be possible that mostly true beliefs are associated with advantageous behavior, but since the semantic content of their beliefs could be anything and it wouldn’t matter, it would be the most serendipitous of coincidences if that were to occur. Similarly on N&E&SPE where even garbage beliefs can be associated with advantageous behavior, it would still be possible that the alien electrochemical reactions causing advantageous behavior also generate mostly true beliefs, but it would be a rather serendipitous coincidence if that were to occur, given the enormous variety of beliefs that can be associated with a given behavior (as the ANPD scenario suggests) and given that we have no further relevant information about the physiology of the aliens.
One could concede that the probability of R given (just) N&E is low but also claim we know some proposition P (perhaps that the physiological relation between beliefs and behavior happens to be benevolent for our species) such that Pr(R|N&E&P) is high, and we have excellent reason to believe that P is true. Therefore, Pr(R|N&E) being low does not defeat R for the evolutionary naturalist. This however would be an objection against the Defeater Thesis rather than the Probability Thesis, so it will not be discussed in this section. Can the Defeater Thesis withstand this objection? For that matter, why accept the Defeater Thesis in the first place?
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 Plantinga, Alvin. “A New Argument against Materialism” Philosophia Christi 14.1 (Summer 2012) p. 21