1. Two philosophies of nature by Edward Feser 1.1 What is the philosophy of nature? The nature of the philosophy ofnature is best understood by way of contrast with natural science on the one hand and metaphysics on the other, between which the philosophy of nature stands as a middle ground field of study. The nature of natural science is itself a topic about which I will have much to say in this book, but for present purposes we can note that the natural sciences are concerned with the study of the actually existing empirical world of material objects and processes. For example, biology investigates actually existing living things - the structure and functionof their various organs, the taxa into which they fall, their origins, etc. ... Astronomy investigates the actually existing stars and their satellites and the galaxies into which these solar systems are organized. And so forth. Metaphysics, meanwhile, investigates the most general structure of reality and the ultimate causes of things. Its domain of study is not limited merely to what happens as a matter of contingent fact to be the case, but concerns also what could have been the case, what necessarily must be the case, what cannot possibly have been the case, and what exactly it is that grounds these possibilities, necessities, and impossibilities. Nor is it confined to the material and empirical world alone, but investigates also the question whether there are or could be immaterial entities of any sort - God, Platonic Forms, Cartesian res cogitans, angelic intellects, or what have you. In addition, metaphysics investigates the fundamental concepts that the natural sciences and other forms of inquiry all take for granted. For example, whereas the natural sciences are concerned with various specific kinds of material substances - stone, water, trees, fish, stars, and so on - metaphysics is concerned with questions such as what it is to be a substance of any kind in the first place. (Is a substance a mere bundle of attributes, or a substratum in which attributes inhere? Are ma­ terial substances the only possible sort? And so on.) Similarly, the natural sciences are concerned with various specific kinds of causal process - combustion, gravitation, reproduction, and so on - whereas metaphysics is concerned with questions such as what it is to be a cause in the first place. (Is causation nothing more than a regular but contingent correla­ tion between a cause and its effect? Or does it involve some sort of power in the cause by which it necessarily generates its effect? Is there only one kind of causality? Or are there four,as Aristotle held?) Whereas the nat­ ural sciences explain the phenomena with which they are concerned by tracing them to the operation of ever deeper laws of nature, metaphysics is concerned with issues such as what it is to be a law of nature and why such laws operate. (Is a law a mere description of a regular pattern in na­ ture? If so, how could it explain such patterns? Why is the world governed by just the laws of nature that do in factgovern it, rather than some other laws or no laws at all?) Of course, some philosophers and scientists deny that there is any reality other than material reality, and any method of studying real­ ity other than [modern] science. That is to say, they defend materialism and scientism. But materialism and scientism are themselves metaphysical positions in the relevant sense. They too address the question whether reality extends beyond the natural world studied by empirical science, and simply answer in the negative. Now, the philosophy of nature stands, as I say, in between natural science and metaphysics. It is more general or abstract than the former, but more specific or concrete than the latter. Metaphysics is concerned with all possible reality, not with empirical and material reality alone. The philosophy of nature is not like that. Like natural science, it is con­ cerned only with empirical and material reality. Natural science, how­ ever, is concerned with the empirical and material world that happens as a matter of contingent fact to exist. The philosophy of nature is not so confined. It is concerned with what any possible empirical and material world would have to be like. What must be true of any possible material and empirical world in order for us to be able to acquire scientific knowledge of it? Are there general principles, deeper even than the fun­ damental laws of physics, which would have to govern any possible mate­ rial and empirical world whatever those fundamentallaws turned out to be? Those are the sorts of questions with which the philosophy of nature is concerned. This is not to suggest that the boundaries between these three fields of study are always sharp. They are not, at least not in practice. The philosophy of nature might be thought of as a branch of metaphysics - as the metaphysics of any possible material and empirical reality, specifi­ cally. Alternatively,it might be thought of as the most philosophical end of natural science - natural science as it begins to stretch beyond what can be tested via observation and experiment and relies more on a priori considerations. As we will see,much work in contemporary analytic phi­ losophy going under the "metaphysics" label in fact recapitulates tradi­ tional themes in the philosophy of nature. We will also see that many claims today put forwardas "scientific" are in factphilosophical, or a mix­ ture of the philosophical and the empirical. Nor are such confusions uniquely modern. Aristotle's Physics was as much a work of philosophy of nature as a work of physics, and the fact that there was no distinction drawn between these fields of study in Aristotle's day or for centuries thereafterled many erroneously to throw the Aristotelian philosophy of nature baby out with the Aristotelian physics bathwater. Precisely be­ cause of such errors, however,it is crucial to emphasize the differencein principle between the disciplines, occasional overlap notwithstanding. How does the philosophy of nature relate to the philosophy of sci­ ence? To a firstapproximation, it might be argued that it relates to it in something like the way metaphysics relates to epistemology. Epistemol­ ogy is the theory of knowledge - the study of the nature of knowledge,of whether knowledge is possible, of the range of our knowledge, and of the ultimate bases of all knowledge. If metaphysics is concerned with the na­ ture of reality itself, epistemology is concerned with how we know about reality. Similarly, it might be said that whereas the philosophy of nature is concerned with the character of the empirical and material reality stud­ ied by science, the philosophy of science is concerned with exactly how science gives us knowledge of that reality. It is a kind of applied epistemol­ ogy,justas the philosophy of nature is a kind of applied metaphysics. However, this analysis is an oversimplification. To be sure, it is not implausible if applied to the philosophy of science as it existed for much of the twentieth century. Logical positivist and logical empiricist philosophers of science like Rudolf Carnap, Hans Reichenbach, and Carl Hempel were hostile to metaphysics, rejected the scientific realist view that the theoretical entities posited by science exist independently of the­ ory, and concerned themselves with the elucidation of the logic of scien­ tific method. Falsificationistphilosopher of science Karl Popper was not hostile to metaphysics or scientific realism,but also focusedon questions of method, as did post-positivist philosophers of science like Thomas Kuhn, Imre Lakatos, and Paul Feyerabend. These major thinkers in the fieldwere indeed largely concerned with epistemological matters. Still, with the revival of scientific realism in the later twentieth century, philosophers of science once again took an interest in metaphys­ ical questions - in the dispute between scientific realism and the various forms of anti-realism, of course, and also in issues such as whether we must attribute real causal powers to things in order to make sense of what science tells us about them, the status of laws of nature, how to interpret what modern physics tells us about the nature of time and space, and so on. What this means, though, is that contemporary philosophers of science have essentially rediscovered the philosophy of nature, even if they don't always put it that way (though sometimes they do, as in the case of Brian Ellis (2002)). In practice, then, there is considerable overlap between the fields. But as with the distinction between the philosophy of nature, metaphysics, and natural science, it is nevertheless important to keep in mind the distinction in principle between the philosophy of na­ ture and the philosophy of science. The emphasis in philosophy of nature is always on metaphysical questions, whereas the accent in the philoso­ phy of science (at least where it isn't essentially just philosophy of nature under another name) is on epistemological and methodological issues. What is the epistemologyof the philosophy of nature itself? Is it an a priori discipline the way that mathematics and metaphysics are often claimed to be? Or are its claims subject to empirical falsification the way that those of natural science typically are? These alternatives are often thought to exhaust the possibilities, but they do not, and seeing that they do not is crucial to understanding how the philosophy of nature differs from natural science. There are propositions that are empirical rather than a priori, and yet which are not subject to empirical falsification. For example, the proposition that change occurs is one we know only through experience. But no experience could overturn that proposition, because any experience that purportedly did so would itself have to involve change.