Nina Emery (Mount Holyoke College), "Mooreanism in Metaphysics from Mooreanism in Physics"
Inquiry: An Interdisciplinary Journal of Philosophy (2024)
By Nina Emery
If you ever really want to get someone who is relatively new to philosophy worked up, try introducing them to G.E. Moore’s “perfectly rigorous proof” for the existence of the external world.[1]
P1 Here is one hand.
P2 Here is another hand.
C1 Therefore two human hands exist.
C2 Therefore the external world exists.
On the face of it, this does not seem like a great argument. It’s simple and powerful, but there is something deeply methodologically suspect about it. You’re trying to prove the existence of something outside of us, and you’re allowed to start with a premise that says we have a hand?
Suffice it to say, I’m not sure I’ve ever seen someone come away from their first encounter with that argument as a Moorean. But why not? There aren’t a lot of uncontroversial starting points in philosophy. Why not start with common sense? There a number of things that non-Mooreans might say in response to this question, but in my experience one of the most common lines of reasoning goes like this: Well, common sense just doesn’t seem like a very good guide to what the world is like. Just look at science – it violates common sense all the time!
This paper is about how that line of reasoning–that science violates common sense all the time, so philosophers shouldn’t rely on it either–while initially plausible, turns out to get things exactly backward. There is a certain type of common sense that plays an important role in the methodology of physics. And because that type of common sense plays an important methodological role in physics, it should do so in philosophy as well. If we use the term ‘Mooreanism’ to pick out views that take some kind of common sense to be a good guide to what the world is like, we get the thesis in slogan form: we get Mooreanism in metaphysics from Mooreanism in physics.
Of course, Mooreanism encompasses a broad and heterogeneous group of views, depending on what one means by ‘common sense’. My argument only applies to one specific type of Mooreanism–the type that uses the way the world appears to us as a guide. The rough idea behind the type of Mooreanism I’m interested in, then, is that the extent to which a theory diverges from the way the world appears to us is an important theoretical cost–such divergence is to be avoided where possible.
Put formally, my focus is on the following principle:
The principle of minimal divergence. Insofar as you have two or more candidate theories, all of which are empirically and explanatorily adequate, you ought to choose the theory that diverges least from the manifest image.
The paper includes all sorts of clarificatory discussion on the meaning of ‘empirical adequacy’, ‘explanatory adequacy’, ‘divergence’ and more, but for our purposes here, I’m going to jump straight to a little preview of the argument.
P1 The principle of minimal divergence is a commitment of standard scientific practice.
P2 If a principle of theory choice is a commitment of standard scientific practice, and that principle favors metaphysical theory A over competing metaphysical theory B, then we ought to adopt metaphysical theory A.
These two premises, taken together lead to the conclusion: if the principle of minimal divergence favors metaphysical theory A over competing metaphysical theory B, we ought to adopt metaphysical theory A.
The support for P1 takes up the bulk of the paper. I begin by setting out a range of what I call radical metaphysical hypotheses. Three examples of such hypotheses (I talk about more in the paper) include:
Solipsistic Idealism. I do not have a physical body or brain. All that exists are my mental states. There is nothing corresponding to the world that I appear to inhabit.
The Simulation Hypothesis. I do not have a physical body or brain. I am a part of a computer simulation which gives rise to my experiences. The physical world, of which the simulation is part, is not at all the way the world appears to be.
The Brain-in-a-vat Hypothesis. I do not have a physical body. My brain is being stimulated in a way that gives rise to my experiences. The physical world around me is not at all the way the world appears to be.
I then ask the reader to notice the following key points: (1) These radical metaphysical hypotheses conflict with our best scientific theories. If any of the above hypotheses were correct, our best scientific theories would be wrong. (2) These radical metaphysical hypotheses are (or can be spelled in more detail so that they are) empirically and explanatorily adequate. (3) What these radical metaphysical hypotheses all have in common is that they diverge significantly from the way the world appears to be. I submit that taken together, these three points give us good reason for believing P1.
Much more can and should be said, of course (and is said in the full paper). But for now I’ll just mention three very common objections to P1. First, when I initially present this premise, it often leaves people sputtering things like, “But…quantum mechanics! Is that a theory that respects the way the world appears to be?!” or “Wait a minute! If science cared about the way the world appears to be, wouldn’t we still think that the sun revolves around the earth?!”
Fair enough, but notice that it is not an objection to P1 to point out that scientific practice often results in theories that diverge significantly from the way the world appears to be. The principle of minimal divergence is not the principle of no divergence. It’s compatible with P1 to think that scientists diverge from the manifest image when they need to in order to maintain empirical or explanatory adequacy.
Second, it’s very common for folks to think that there is something suspicious about my appeal to the radical metaphysical hypotheses. They say things like, “well these aren’t candidate theories at all” or “scientists don’t take these theories seriously”. That may be. But the principle of minimal divergence and the argument as a whole is easily adjusted to handle this. We just change the principle to be about which theories to take to be genuine candidate theories, or which theories to take seriously, and mutatis mutandis, the argument will go through.
A third and related point is that sometimes my interlocutors try to avoid the principle of minimal divergence by telling their own story about what is wrong with each of the radical metaphysical hypotheses. Solipsistic Idealism isn’t very explanatorily powerful, they say, and the Brain-in-a-vat hypothesis is unnecessarily complicated. This is all well and good, but notice that the strength of the argument is in taking the radical metaphysical hypotheses as a group. This group is highly heterogeneous in terms of the types of theoretical virtues that its members exhibit–some are very simple, while others are quite complex, and so on. Thus any alternative explanation of why the radical metaphysical hypotheses are ruled out (or not seriously considered, or whatever) by scientific practice is going to be piecemeal and complex. A much better, more straightforward explanation is that the feature that all of these views have in common is a feature that scientific methodology shies away from–and that feature is divergence from the manifest image (while maintaining empirical and explanatory adequacy).
So much for P1. What about P2? This premise is a statement of a certain kind of naturalism–methodological naturalism. In general, I find that readers of this paper are far less suspicious of this premise than they are of P1, for obvious reasons: science is a paradigm of successful inquiry into what the world is like, so surely the default view in metaphysics ought to be to respect any methodological principles that show up in science.
For what it’s worth I think the question of whether we should be methodological naturalists, and what exactly the view commits us to, is for more complicated and far more interesting than that mini-argument suggests. In fact, I wrote a whole book about it—Naturalism Beyond the Limits of Science, Oxford University Press 2023—in which the argument about Mooreanism we’re discussing here appears as a case study. Those looking for a detailed exploration of P2 will find it in the first few chapters of the book. Spoiler alert: In the end, I agree that we should be methodological naturalists, but I also think that if the consequences of the view are fully appreciated, they will require significant changes in the way we do philosophy.
But back to ‘Mooreanism in Metaphysics from Mooreanism in Physics’. The conclusion of the argument is that we should use the principle of minimal divergence to guide our metaphysical theorizing. What philosophical consequences follow? In the paper I go through how the minimal divergence norm applies to compositional nihilism–the view that there are no composite objects. (And yes, I talk about how it applies even if you’re a compositional nihilist who maintains that the world appears to us to contain simples-arranged-chair-wise and table-wise and so on.) But that’s just one example. I’ve also used the principle in other work to argue against certain views in quantum ontology.[2] And there are plenty of other opportunities to explore applications of this principle. Any time we are tempted to dismiss the ‘common sense’ position in a philosophical debate, we ought to pause and look more closely–would doing so violate the principle of minimal divergence? If so, then we should resist.
Indeed, by way of conclusion let me emphasize an important sense in which the consequences of my argument are more expansive than they may first appear. Although this paper is about metaphysics, the conclusions don’t only apply to those of us who put metaphysics as an area of specialization on our AOS or who work on classic questions about modality or composition or personal identity. Metaphysical questions are just questions about what the world is like, and they crop up all over philosophy. When philosophers of mind ask, “What is consciousness?” they are asking a metaphysical question. The same goes for moral philosophers asking about the nature of right and wrong or philosophers working on aesthetics asking about the nature of beauty. Indeed, I think it’s a rare philosopher who doesn’t do at least some metaphysics. So if I’m right about the argument in this paper, then the conclusion applies to all of us. We might scoff at G.E. Moore’s “perfectly rigorous proof”, but there’s something in the vicinity of such appeals to common sense that is very much on the right track. We should be Mooreans after all.
[1] Moore, George Edward (1939). ‘Proof of an External World.’ Proceedings of the British Academy 25 (5):273--300.
[2] Emery, Nina. 2017. Against Radical Quantum Ontologies. Philosophy and Phenomenological Research 95 (3):564-591.