Necessitarianism Isn’t that Weird

Necessitarianism is the view that everything in the actual world is metaphysically necessary. Things could not have been any different: the actual world is the only metaphysically possible world.

The usual reaction to this thesis is an incredulous stare. How could it be that things could not have been any different? It sure seems like some things are contingent. I could have worn a red shirt today; I could have poured an extra bit of water in my morning bowl of kale; my local library could have had one less book than it actually does; there could have been 5 fewer blades of grass in Central Park than there actually are. It may seem pretty implausible to suggest that things had to be precisely as they are. It really isn’t even possible that my dad could have had one additional strand of hair?

In this post, I’ll try to convince you that this view is not as crazy as it might sound.

It is important to keep in mind that the kind of possibility we have in mind here is metaphysical possibility — metaphysical possibilities are ways the world “really could have gone”. This is distinct from logical possibility. Logical possibilities are simply consistent descriptions of the world, but not necessarily ways the world really could have gone.

A few examples might help. Theism is one way to illustrate the concept of metaphysical possibility. On theism (as I’ll use the term here), it is metaphysically necessary that God exists. The world couldn’t have been such that God doesn’t exist: He has to exist. But this is not to say that there is some contradiction that can be derived from the statement “God does not exist”. It is perfectly consistent (with all logical theorems) that only a single particle exists. That is a coherent state of affairs. Nevertheless, it isn’t one that, for the theist, is genuinely possible for the world to have been like: reality is actually such that a metaphysically necessary being is the foundation of everything. If the theist is right, the single-particle world is internally coherent, but it is not a way that things could have actually gone.

A perhaps more helpful example is moral realism. Suppose there are moral facts — stance-independent facts about (eg) what you have reason to do. The standard view is that these facts are metaphysically necessary. It’s not as though in our world horrific torture is bad, but things could have been such that horrific torture is good. No, says the moral realist. Moral facts are inextricable parts of the fabric of reality: they are metaphysically necessary. That’s not to say that moral anti-realism entails a contradiction. There’s nothing strictly inconsistent about the proposition ‘there are no stance-independent moral facts’. I

Perhaps another helpful way to think about this is that we can imagine that, just as there are laws of physics, and ‘laws’ of logic, there might be ‘laws’ of metaphysics. Even if we vary how our world physically is (eg, imagining different initial conditions, different laws of physics, different fundamental forces), there are features of the world that are invariant: whether there are moral facts, whether God exists, etc. So ‘metaphysical possibilities’ are all the ways the world could have gone that are consistent with these ‘laws’ of metaphysics.

So, necessitarianism is the view that everything is metaphysically necessary — there are no ways for the world to go other than how it actually goes. Here are some reasons we shouldn’t so confidently dismiss this view.

First, we shouldn’t act like we have direct intuitions about metaphysical modality. Consider that what the metaphysical possibilities are depends deeply on what reality is essentially like. For instance, if reality is essentially divine (i.e., a perfectly good God exists as its foundation), then it will likely turn out that reality can’t go such that totally gratuitous evil exists. But, if reality is essentially naturalistic, this seems like a totally possible way for things to go!

This is why we should not claim to have much of an a priori grasp on the ways reality could go. Indeed, we should find this kind of claim — that we know a priori (!) the different ways reality could go — extremely implausible. Because we do not know, a priori, what reality is like! So how are we to know, a priori, the different ways it could go?

Now, you might respond that, when you reflect on the way our world has gone, it sure seems like things could have been different: things could be smaller or bigger, events could have happened slightly differently, history didn’t have to go exactly as it did, etc. But we should be careful about what these intuitions tell us. These intuitions are pretty great evidence that all these alternative scenarios are logically possible. The fact that I can vividly imagine, conceive, and construct such scenarios is pretty good evidence that they are internally consistent, do not violate any logical theorems, etc. But why is the fact that these scenarios are coherent (imaginable, conceivable, etc.) strong evidence for the view that these scenarios are really ways the world could have gone? Again, that depends on what the essential features of reality are like, and whether they are consistent with those alternative scenarios we imagine.

Maybe the thought is that these alternative scenarios are just so similar to the actual world, or just so benign, that it would be really weird for the essential features of reality to rule them out. But this is a really strained inference. I don’t think we should have much confidence in what reality rules in or out until we have actually given arguments and directly thought about what reality is like.

Now, this has all just been defensive: I’ve just been claiming that I don’t think we have much evidence (a priori) against necessitarianism. Let me give you some positive reasons why one might think necessitarianism is true.

First, if one is a theist, one might be inclined to think necessitarianism is true. If God is perfect, plausibly, he would only do what is best. Just as God would necessarily not make there be gratuitous evils, God wouldn’t actualize what is inferior or imperfect. But, if there’s only one state of affairs that is best, then that state of affairs (the perfect world) is necessary. In other words, if reality is essentially and necessarily divine, it wouldn’t be too surprising for reality to be necessarily perfect — and there might only be one way to satisfy the description ‘perfect’.

Second, if one thinks that there is a necessary being at all. A very trendy response to contingency arguments is that some aspect of reality is necessary, but it needn’t be God — it could be that a wave function, or some other deep physical theory of everything, is necessarily the foundation. But there is good reason to think that this necessary being would also entail how reality is. It would be at least a bit odd if the necessary being indeterminately causes things to be one way rather than another: the particular distribution of the objective chances would have to be a brute fact, and we’d fail to have any sufficient explanation of why things are one way rather than another.

Third, strong variants of the Principle of Sufficient Reason. This sort of argument is likely why the early Leibniz and Spinoza embraced necessitarianism, and is the basis of van Inwagen’s argument against the contingency argument. Very, very roughly and imprecisely: If one thinks that for any fact, there must be an explanation of why p rather than ~p, one will likely end up thinking that necessitarianism is true. For either this series of explanations bottoms out in a necessary being that entails how things go, or else there is an infinite (or circular) series of sufficient explanations. The former option entails necessitarianism. Proponents of the latter will probably have to embrace that the fact that this entire series of explanations exists is itself necessary (i.e., it couldn’t have been otherwise), or else they haven’t fully explained every fact.

Fourth, huge multiverses. Imagine that the actual world is much larger than we suspect: rather than only our universe existing, many other universes exist. Indeed, imagine something like David Lewis’ modal realism is true: every consistent way for reality to go is in fact a concrete universe that exists, spatiotemporally isolated from our universe. Every one of those alternative scenarios we imagined earlier — me wearing a red shirt today; an extra bit of water in my kale; my local library having one less book; there being 5 fewer blades of grass in Central Park — are alternative universes that concretely exist. So, reality is an unbelievably large multiverse. On this view, this entire multiverse … exists necessarily! It couldn’t have been different. And is that so weird? Whatever way you imagine reality being different is in fact a way that a certain universe within this multiverse is.

Now, I don’t think we should take any of these that seriously as arguments. At least not without me being way more precise and saying much more. But that is not my point: I do not want to convince you that necessitarianism is true. What I want to show you is that we shouldn’t think it is some super implausible view that is a death blow to any view that entails it. Instead, we should think about things in the following way: to figure out what the metaphysical possibilities are, and how many there are, we should reason about how reality is like. On many theories of reality — theism, necessary-foundation theories, and other views on which every fact is fully explained — there aren’t alternative ways the world can go, because there is something essential to reality that entails (explains!) how things go. So it may well be that necessitarianism is true. Alternatively, it may well be false — especially if reality is essentially indeterministic (as deliberation about quantum mechanics and free will might unveil). But too often it seems that philosophers hold fixed that there has got to be contingent in various ways, and then they reason backwards from there. This is unfortunate.