it is because of this success—the comparative simplicity of Copernicus’ theory—that we rightly look back at Copernicus’ theory as a momentous step forward in our theorizing about the motions of the planets, even if it does take a step backward on the rubric of fit with the data. Thus, the method of evaluating theories by their simplicity, however that method works, is not merely a tiebreaker to be deployed as an afterthought. We can see that sometimes we think we are justified in losing some fit with the data for the sake of a greater gain in simplicity.
Truth is the first virtue of systems of thought, but I just said that we are sometimes justified in losing some fit with the data for the sake of a greater gain in simplicity. How can this be? Doesn’t losing some fit with the data for the sake of a greater gain in simplicity constitute trading some truth for something else, simplicity? This is a puzzle. But notice that theories and explanations are, by their very nature, systematic: they are systems of thought, not mere lists of thought, mere lists of truths. Now, what makes a good system? What makes a system, in virtue of being a system, a good system? The answer is implicit in our consideration of the simplicity method of theory evaluation. A mere list of data, even if it’s completely true, is not a good theory because it’s not a good system of thought. A convoluted theory with layer upon layer of ad hoc hypothesis, even if it fits perfectly with the data, is not a good theory because it’s not a good system of thought. A system is a good system if it is, for example, simpler, more unified, more economical, more coherent, more elegant, etc. In a word, a system is a good system if it is beautiful.9
This is a bold and striking claim, but it is one that I will argue for in this book. If it is true, then it will follow that beauty is relevant to our evaluation of theories. If beauty is what makes a system good as a system, then theories, which are systems of thought, will be better as systems if they are beautiful. That is the thesis of this book: judgments of beauty are part of how we evaluate theories—how we discover which theories are better. That is, a theory’s beauty is part of what makes it better.
There is significant dispute in contemporary philosophy of science on whether judgments of beauty do or should play any role in scientific theorizing.10 If my arguments for my thesis are successful, obviously this project will bear on that dispute. But it should be noted that I mean my thesis to be broader in scope—applying to all kinds of theorizing endeavors, including philosophy, science, and “ordinary” theorizing (such as the Colonel Mustard case). Indeed, in contrast to the debate in the philosophy of science, I will mainly focus my attention on philosophical theorizing (hence my beginning with competing theories of justice), although some examples of scientific theory evaluation will be used. Disputes in philosophy of science about the role of beauty in scientific theory evaluation are often narrow and attend to special features of scientific theorizing (e.g., the especially empiricist or mathematical methodologies of scientific theorizing). But this means that these disputes often neglect potential connections between philosophical theory evaluation and scientific theory evaluation, even though values like simplicity and coherence are relevant to both philosophical and scientific theorizing. This is made pointed by noting that attempts to theorize about the structure of scientific theory evaluation are themselves philosophical theories, not scientific theories (given that philosophy of science is a branch of philosophy, not science). If judgments of beauty are relevant to all theorizing, then philosophers of science who are concerned with judgments of beauty will also need to take a step back and consider the role of judgments of beauty in their theorizing about science. I hope this project can provide an avenue for connecting the philosophy of science dispute over judgments of beauty with larger questions about the nature of beauty and other kinds of theory evaluation, including philosophical theory evaluation.
My thesis—that judgments of beauty are relevant to theory evaluation—should not be understood to deny the important claim that I started with: that truth (or some other epistemic good) is the first virtue of systems of thought; we must reject systems of thought, no matter how beautiful, if they are not true. I will not argue that we should sometimes abandon truth for the sake of beauty in our theories. But we do not have direct access to the truth of theories. We must rely on methods of theory evaluation that point to some other property, which acts as a middle term between theories and truth. And I will argue that beauty is one such middle term, alongside familiar methods like fit with the data and the principle of noncontradiction. Truth is the first virtue of systems of thought, but we need beauty to help us discover which of all the competing theories is true.
Outline of Chapters
The first step in arguing for this thesis is to immediately defuse the most common objection that philosophers and lay readers alike will tend to have: that beauty is thoroughly relative and thus utterly unsuitable for having any connection to truth, which is not relative. This objection is most commonly expressed by citing the aphorism “Beauty is in the eye of the beholder.” The objection by means of this aphorism is not as straightforward as it might seem and thus it will have to be worked out what exactly this aphorism means and whether it does generate problems for my thesis. But whatever the aphorism means, thoroughgoing relativism about beauty would indeed be a problem for my thesis and thus I will argue directly against thoroughgoing relativism about beauty. I will do this by undermining common arguments in favor of thoroughgoing relativism about beauty, by arguing that thoroughgoing relativism about beauty has deeply counterintuitive implications, and by drawing an analogy to thoroughgoing relativism about morality. I will do all this straightaway in chapter 1.
After that initial problem is dispelled, I can take positive steps toward my thesis. The first step is to give an account of the nature of judgments of beauty. I won’t make it my purpose to give a full theory of beauty in this book, I want to leave my thesis compatible with as many full theories of beauty as possible. But a key piece of my thesis, as I said above, is that beauty is the thing that makes systems good as systems. This needs explaining. By giving a mid-level account of beauty—not a full theory, but still making important claims about the nature of beauty—I will explain why judgments of beauty are the relevant kind of judgment for evaluating systems. This mid-level account of beauty will be inherited from Kant and Mary Mothersill and will hold that the distinctive nature of judgments of beauty is that they are unprincipled—made without any reference to principles—and yet can be genuine—we can nonarbitrarily distinguish good judgments of beauty from bad judgments of beauty. I will explain why this entails that judgments of beauty are the relevant kind of judgment for evaluating systems. This account of beauty will be developed in chapter 2.
Once I have this mid-level account of beauty—judgments of beauty are unprincipled, yet possible—I can begin in earnest the argument for my thesis: that beauty is relevant to theory evaluation. I will begin this argument by illuminating how this might work by examining in detail some important methods of theory evaluation. First, in chapter 3, I will examine the method of reflective equilibrium and explain how this sophisticated method works. Reflective equilibrium is closely related to fit with the data, but also importantly uses the concept of coherence to evaluate theories. I will argue that coherence is best understood as a species of beauty, given the account of beauty I will develop. This will mean that reflective equilibrium is an example of my thesis at work. Then, in chapter 4, I will examine the method of simplicity: the method that holds that simpler theories are better theories and thus that judging a theory by its simplicity is a justified means to finding better theories. The concept of simplicity needs explaining if it is to form the basis of a fully worked out method of theory evaluation. I will likewise argue that simplicity is best understood as species of beauty, given the account of beauty I will develop. Again, this will mean that the methods of simplicity is an example of my thesis at work. Examining these methods—reflective equilibrium and simplicity—and finding that judgments of beauty are part of how these methods evaluate theories will illuminate how my thesis is supposed to work—how judgments of beauty are relevant to theory evaluation. To find my thesis implicit in such powerful and widely used methods of theory evaluation will also constitute an argument in defense of my thesis, inasmuch as we take these methods of be justified methods of theory evaluation.
But
