Another argument for the PSR

The PSR is the Principle of Sufficient Reason, the most controversial premise of the LCA which we have defended here previously. We will here provide another argument for the PSR. That is, for the claim that for every contingent thing (or perhaps indeed every single thing, contingent or not) has a sufficient explanation.

The argument I intend to motivate is this: we should extend reasoning principles as far as possible, until we have a good reason. The PSR is a principle we use in many areas, and so we should extend it to all objects unless we can come up with a good reason why we should not.

Now we all know how we apply the PSR in physical situations. There is currently light hitting my eye, as an explanation I posit a computer monitor in front of me as an explanation. An apple falls from a tree, and we posit gravity. Celestial objects move across the sky, and we posit heliocentrism. In none of these cases do we say “perhaps there’s no explanation”, we always immediately begin looking for one. If there’s some phenomenon we can’t find an explanation for, we conclude that we aren’t smart enough, or our equipment isn’t precise enough. We assume that there is one we just haven’t found.

So now we might be tempted to say “The PSR only applies to physical phenomena”, and then we wouldn’t be forced to admit that God exists. And there may be some cause for this since intuitively, physical objects are the kinds of things which seem like they’re causally closed. But maybe other kinds of phenomena (if they exist at all) are “spooky” and not causally closed, so maybe there’s no PSR there.

Let’s consider another domain then: ethics. Take the famous trolly problem: suppose it turned out to be the case that it was morally wrong to pull the lever to save five while condemning one. Suppose this was morally impermissible. And an interested interlocutor would ask “Why?” Suppose we answered, “It just is, there’s no reason”. Is that an acceptable answer? Clearly not. And in fact many ethicists have spent their lifetimes looking for answers to such ethical question: what is right and what is wrong, and why are those things right and wrong. Again, there is the presumption of explanation.

Now a third domain: mathematics. We observe some mathematical phenomenon, and we ask “why”. That “why” often comes in the form of a proof, or at least a sketch of a proof. Often the “why” is actually hidden in the proof, almost as if the author of the proof went to great effort to obscure the deep intuition. But sometimes it’s on the surface. And this doesn’t only apply to theorems, we can ask why a theorem is true, but we can also ask why something more general is the case. Here’s one such question: why does the sum of the series of inverse square numbers involve a pi term? Pi has to do with circles, but this doesn’t appear to be related to circles. And indeed, there is an explanation.  This kind of question is often asked by mathematicians, why is something the case? And often the answer is intuitively satisfying, deep, and can lead to new ways of thinking about problems. Much of mathematics, rather than hunting for proofs of theorems, is hunting for these more intuitive, conceptual explanations of a more general class of phenomena.

Now we go back to our PSR. It holds in the domains of physics, ethics, and mathematics. Our natural, everyday reasoning assumes that the PSR holds when we consider physical objects, abstract objects (such as numbers), and moral facts. So how might we restrict it? If we say “All physical, ethical, and mathematical phenomena have sufficient explanations”, but that seems extremely arbitrary. And again, we normally want to expand principles until we have a good reason not to. What good reason do we have for restricting the PSR to these classes of phenomena, but not others?

And we can take this argument even further. We can follow Della Rocca, and point out that unless you can give a sufficient reason for that restriction, you’ve begged the question. I covered that particular argument in the original post on the PSR, but it is worth reiterating because I think it is indeed a strong one.

 

 

Laying the Groundwork for the LCA: The PSR

The Leibnizian Cosmological Argument is one of my favourite arguments for God. The LCA can be summarised in this way:

  1. Every contingent fact has an explanation.
  2. There is a contingent fact that includes all other contingent facts.
  3. Therefore, there is an explanation of this fact.
  4. This explanation must involve a necessary object.
  5. This necessary object is God.

 

Today we are only going to discuss point 1. And this will probably not be our only discussion of this point, as there are many levels of counter arguments and responses to those that we will need to discuss at some point. This premise is called the Principle of Sufficient Reason.

A more general formulation (Taken from the SEP) is given as: For every fact F, there must be an explanation why F is the case. There are several good arguments for accepting the PSR, but so far there’s no proof of it.

First, if we do not accept the PSR, I would argue that we must accept some unfortunate consequences. I believe that I’m currently sitting in front of my laptop typing things into it. I believe this because I can see it. Because there are photons bouncing off my laptop (or emitted from the screen) and entering my eyes. But if the PSR is false, then there’s no reason to think that anything actually caused those photons to exist. Not just that I might be a brain in a vat being fed sensory information, or deceived by an evil demon like Descartes might suggest, but that there may be no explanation for the sensory information at all.

If we don’t take the PSR, then we can’t look at facts and try to work out the best explanation. Sherlock, for example, takes in a lot of details and provides usually a good explanation for why the facts are that way. But he never includes in his reasoning the option that there’s no explanation. Neither should we. We should look for explanations, and so we must always assume that there is one.

If the PSR is not true, why don’t we see lots of violations of it? If I saw a soccer ball materialize in front of me, I’d probably look for an explanation. But if the PSR weren’t true, there’d be no reason to look for an explanation. It could just be a brute fact that the soccer ball exists there. No explanation for why it is there.

Which brings me to the next argument: even if there’s not always an explanation, we ought to believe that there is one and look for it. Consider the example of the theory of evolution: what is the explanation for the variation of species? Normally, we’d say something like evolution via random mutation and natural selection. We’d justify that claim by pointing out the large number of observations that confirm it. But how do these observations confirm it? They confirm it via the PSR: we believe that evolution is true because it is the best explanation for our observations.

But how did we determine that there was an explanation here? The fact is that we didn’t, and we would have no way of doing so. We assumed there was, and we looked for it. But a Creationist who responds to the evidence for evolution with “Perhaps there’s no explanation” would be rightly ridiculed. We value explanations over no explanation, even if we can’t conclusively show that there is no explanation. We ought to believe there is one, even if there isn’t.

A more complex argument comes from Della Rocca. I link his paper below, and I will give a summary (and occasionally steal parts verbatim) of his argument here. First, he establishes that in every-day reasoning, we use something he calls “explicability arguments”. Something like this: no explanation for a state of affairs means that state of affairs cannot attain. Consider this: we have a scale with a weight on either side. If the weights are equal (and the scales are fair, and there are no outside influences), we know the scale will be balanced. How do we know this? Because there is no reason the scales would be unbalanced, there is no explanation as to how that would happen, so it cannot be the case. We reject the possibility of an unbalanced scale because it has no possible explanation. Or another example: suppose we have two substances. Suppose they are identical in every way, that they have the same chemical makeup, same structure, etc. One dissolves in water. We know that the other will dissolve in water too. Why? Because there is no reason why it would not, if one has the disposition to dissolve in water, how would the other fail to have this disposition? If they are identical, nothing could ground this difference, so we reject the possibility of them behaving differently.

In fact, it seems like avoiding inexplicability is a main motivator to naturalism or physicalism or materialism. We want to avoid believing in things that can’t be explained (such as the supernatural). The naturalist says that if it cannot be explained naturally, it does not exist. Again, they affirm the PSR in this context.

If we can use these arguments in general, then the PSR follows easily. Clearly we want to take a limited PSR in some local contexts. But can this kind of reasoning apply in general? Someone who denies the PSR might claim that it applies to some situations, but not others. But we claim that there is one example where we use inexplicability arguments where we can’t appeal to a local PSR without doing so arbitrarily and question-beggingly. And it is precisely the case in question in this argument.

What is it in virtue of which something exists? The existence of each thing that exists must be explicable. When we have causation, we ask why it is that this is a case of causation. So when we have something that exists, we ask why it is the case that this thing exists. The denier of the PSR attempts to draw a line somewhere, and explain why we can use a PSR in some contexts, but not in the existence context.

The denier of the PSR must draw this line in a principled, non-arbitrary way. This is because to draw the line in an unprincipled, arbitrary way is to say that there is no explanation or no reason why the law is drawn in this place. But to say that there is no explanation is to say that the PSR is false. And surely people cannot be allowed to assume the PSR is false when they are trying to argue against the PSR. That would be circular, I may as well assume God exists when trying to argue that God exists.

So of course, this line must be drawn in a principled, non-arbitrary way. And of course there is no such way. If you and I want to use the kind of explicability arguments above, then you and I need to come up with some reason why they work in some cases and not others. And unless we do come up with such a reason, we must accept the full PSR.

Further reading: