One often hears the argument that it is not reasonable to analyse the likelihood or otherwise of a supernatural and transcendent deity using scientific means, as such a deity is, by definition, outside of the material universe – and is thus beyond science’s sphere of applicability. In answer to that, I would firstly point out that we have no evidence that there exists anything outside of the physical world (i.e. supernatural). However, even if we are to suppose that some supernatural entity does exist, we nevertheless seem to be limited in our enquiries to the material world alone – as that is the world that we inhabit. Hence, we can only attempt to infer the existence of such a supernatural entity by searching for traces of its effects upon the material world. So, in order to make any progress with this question, we need to frame our supernatural entity hypothesis in such a way that it makes predictions about the material world that we are able to investigate.
I would further point out that if we were to persist in the requirement that any supernatural event or entity is forever beyond scientific investigation, even in principle, then we are actually saying that no such thing (or effect of this thing) can ever be observed. For, if it can be observed, then it can also be investigated scientifically. If we hold this view, then we believe in the existence of something that we have no way of ever verifying or falsifying. It exists as a metaphysical construct only. Whilst it might be interesting to construct such a metaphysical hypothesis, I would contend that it is not rational to believe that it exists in reality unless one has some good reason for doing so (beyond mere wishful thinking).
If we are to really make any progress on this question, then how would we define a supernatural event? As a starter, I would suggest Keith Augustine’s definition for a candidate supernatural event: “(1) the cause of the event cannot be identified as any known physical force or entity nor is it supervenient upon any known physical force or entity; (2) the cause of the event cannot be located in space and time; (3) the event defies all attempted scientific explanations thus far; (4) the event appears to violate well-established scientific laws (as distinguished from genuine laws of nature); (5) the event is highly improbable if it solely has known natural causes; and (6) the event exhibits apparently purposive or intelligent behaviour.”
As far as the concept of the supernatural that is disallowed by metaphysical naturalism, the following definition explains it well: “What all metaphysical naturalists agree on, however, is that the fundamental constituents of reality, from which everything derives and upon which everything depends, is fundamentally mindless. So if any variety of metaphysical naturalism is true, then any mental properties that exist (hence any mental powers or beings) are causally derived from, and ontologically dependent on, systems of nonmental properties, powers, or things. This means metaphysical naturalism would be false if any distinctly mental property, power, or entity exists that is not ontologically dependent on some arrangement of nonmental things, or that is not causally derived from some arrangement of nonmental things, or that has causal effects without the involvement of any arrangement of nonmental things that is already causally sufficient to produce that effect.
In lay terms, if metaphysical naturalism is true, then all minds, and all the contents and powers and effects of minds, are entirely constructed from or caused by natural phenomena, while if metaphysical naturalism is false, then some minds, or some of the contents or powers or effects of minds, are causally independent of nature, either partly or wholly caused by themselves, or existing or operating fundamentally on their own. Belief in the latter entails some form of supernaturalism (the opposite of naturalism), which is not limited to supernatural beings, but can encompass mindless things with distinctly mental properties, like magical objects, or causally efficacious Platonic Forms or the existence of Love as a cosmic force.”
Now, when we investigate the material world, we should do so scientifically, as this is by far the most successful methodology that we have at our disposal for such an enterprise. It combines logic with observation (not to mention peer review) in the most rigorous way that we have so far been able to invent. Now, you may try to argue that we cannot investigate the non-material world scientifically, but that is not what we are attempting to do here. I repeat, as this is the crux of the argument, that since we appear to be limited to the material world (and have no direct evidence that any supernatural realm exists at all), we have no choice but to attempt to infer the existence of the supernatural by looking for its effects within the material universe. Therefore, that objection is just a red herring. For, if we are not able to observe any supernatural event or entity, then it is not rational to presume that such things exist at all.
On a mundane level, this involves testing psychics and the like by carrying out empirical tests of their supposed powers. They have framed their assertions in such a way that the purported phenomena should be detectable to us in the material world. Therefore, if they are not detected, then the psychics’ hypotheses are falsified. By contrast, if we were able to consistently reproduce some event that fits the definition of supernatural given earlier, then we would have some explaining to do. Is it actually supernatural – therefore falsifying metaphysical naturalism – or is it some as yet unexplained natural event? It would need careful analysis. However, do date no such event has been consistently observed.
Similarly, in order to investigate the supernatural god hypothesis, we need to frame it in such a way that it makes predictions about what we would expect to observe in the material universe. If we are not able frame our god hypothesis in such a way, then it cannot be investigated at all, as we have no other means at our disposal. Logic alone will not do here, as we can formulate any number of hypotheses that would pass the logical consistency criterion. Furthermore, there are logical issues with the god hypothesis anyway, as I pointed out in another post.
Now, some may argue that their favoured god hypothesis makes no predictions about what we would expect to see in the material universe, or predicts exactly what we observe already. In such a case, there is no reasonable argument to be made for believing it. By contrast, the types of hypotheses advanced by many theists (for example, an all-powerful, all-knowing, and all-good God who is specifically interested in humans) do make many predictions about what one would expect to observe in the universe. Almost without exception, these predictions are not met in reality, so the hypothesis is almost certainly false (and is clearly not the best explanation available).
So, to summarise, we are justified in investigating our god hypothesis scientifically, as this is all that we can do. That is not to say that the supernatural cannot possibly exist, but rather that as we seem to be confined to the material world and, when investigating the material world, the scientific method is our best bet. So, we have no choice but to frame our hypotheses of supernatural entities in such a way that they make predictions about what we would expect to observe, and test these.
If you disagree, then how would you propose that we test our supernatural god hypothesis in any other way than by observing the material universe?
See here for a very interesting discussion of this topic.