To investigate the connections between rationalism and materialism I will entertain here what some may think of as an extreme version of rationalism , which consists of two principles. One is that we should only believe to be true statements that are supported by reasons (either by evidence or deduction), and that when several mutually exclusive alternatives are supported equally the easiest to falsify should be adopted (or, in other words, the one that makes the strongest claims, or the simplest; all three criteria usually support the same choice). I call this a radical version of rationalism because many versions of “rationalism” accept the idea that some things can be rationally known through intuition, an idea that doesn’t seem rational at all to me.
Foundationally we might ask why we should accept these principles as guides for thought. After all there are many possible ways of reasoning, labeling this one as rational doesn’t necessarily make it the best. It might be possible to construct a defense of rationalism based on some other, more universal principles, but I won’t bother, since history has shown that rationalist methods of approaching problems have always led to the best results, the most promising theories, the most reliable technologies. Other approaches may have had more followers than rationalism, for example the method of believing whatever you have been told (dogmatism), but none of them have come anywhere close to rationalism in achieving real results. Of course this doesn’t prove that rationalism is the universally best way of reasoning right off the bat, but given that we accept it within some domains we can ask the question: “are these domains all that rationalism can be applied to?” Since there is no rational reason to believe that rationalism is limited we should be compelled to accept that it is a universally good strategy, until proven otherwise.
Given then these rational principles, and reason to think they are universally applicable, we should be naturally led to ask: is it possible to reconcile rationalism with the idea that something non-material exists? Another way to put this idea might be to ask: is there any observation where a non-material explanation will be better than a material one ? Obviously the answer to that question must be no, because generally it is impossible to falsify non-material explanations of phenomena, but it is easy (or at least easier) to falsify materialist explanations, since one expects material causes to be observable. For example, the thesis that tiny creatures cause disease is more rational than the idea that disease is caused by evil spirits; the tiny creatures hypothesis could be disproved with the correct observations. This holds true even if one currently can’t build a microscope, because could eventually hope to construct one, but never an evil-spirits detector.
Of course when considering explanations about past events considerations of what is rational become trickier. Certainly we can still use our criterion of being supported by reasons to eliminate some bad theories, for example the hypothesis that aliens built the pyramids is supported by evidence to a smaller degree than the theory that slaves built the pyramids. In some ways we might also still be able to use the criterion of falsification, since surely more information will be revealed to us by archeological finds, and this new evidence will have the possibility of falsifying some theories (for example, evidence of alien graffiti). However, let us assume that we are in a position of having all the evidence and that the evidence equally supports two theories. In this case I would have to say that neither is more rational than the other, which doesn’t invalidate our rationalist requirement, but does illustrate how much harder it is to acquire knowledge when new experiments can’t be done to test hypotheses.
The reason I bring up considerations of past events because it is possible to form a hypothesis to the effect that something non-material existed in the past, and not have this hypothesis be defeated simply on concerns of testability. However, as mentioned above, the historical data will support different hypotheses to different degrees, and thus the non-material hypothesis will be passed over in favor of material ones . And since the non-material will never be supported by rationalism, either as an explanation of phenomena in general or past events in particular, we can conclude that rationalism, or at least this form of rationalism, leads avoidably to materialism.
1. Strictly speaking this might be a view that could be reconciled with the traditional doctrines of “rationalism” at all. This is however irrelevant to the current discussion, in which I am more interested in considering whether principles of rational thought, which I will call rationalism for convenience, lead to materialism.
2. Of course some of this argument turns on exactly what we mean by material. For example photons aren’t “material”, but certainly we still consider them part of the material world. For simplicities sake I will define material as anything that interacts with the observable world in a predictable way, allowing us to theorize about it and predict its behavior. Generally spirits and other such non-material entities are not considered accessible to such scrutiny and prediction, and hence non-material. If one could built spirit detectors and create reliable theories of spirit particle physics then it would make such spirits simply another part of the material world, and not really “spiritual” at all.
3. Evidence A can only support explanation B if it is known that B is the most likely cause of evidence A. The non-material however will never be thought of as the most likely cause, because it must be, by its nature, unpredictable, and thus we would never have reason to believe that it was the most likely cause. If the non-material could be reliably known to be the cause of certain events that would make it simply another part of the material world, as mentioned above.