Ontology is something of a fad in philosophy; sometimes it is regarded as the core and foundation of metaphysics, and at others it is held up as an example of what not to do. But what is ontology? Ontology, like philosophy in general, is an activity – something that philosophers do. The practice of ontology produces a system of categories, a division of the world into distinct kinds of things. What these categories are supposed to reveal is debatable. Many say that the category system sheds light on the nature of being by revealing what kinds of being there are. (This is where the word “ontology” comes from, it literally means the study of being.) Others of a less metaphysical bent say instead that the categories reflect fundamental divisions in the world. In any case the results are taken to be deep and important in some way.
Ontology as it is customarily conceived is a questionable practice. Focusing in the results rather than the process, as is common, some ask the ontologist “how do you know?” Where does the knowledge of how to divide up the world into parts come from? And what sort of reasons are there to favor one proposed category system over another? For there certainly are an abundance of them. The ontologist has no good answers to these questions. He has many bad ones of course – bad answers seem popular in the defense of philosophy. He might say that he has some special insight into the nature of the world that his ontology reflects. The questioner obviously lacks this insight, if he is raising such questions, and so this answer doesn’t go far. Since some special insight is about the only way to justify claims about the fundamental nature of reality that are not obvious to everyone the ontologist often retreats at this point. Ontology is presented as merely a study of concepts, or of language, or of the forms of experience. These answers are equally unsatisfying, this time because they make ontology significantly less interesting, and possibly not philosophy proper at all.
The root of these problems does not lie in ontology though, but in the ontologist and his questioner. And their problems are rooted in the history of philosophy. Before the modern era there was no such thing as philosophy, and no such thing as science. There was instead philosophy-science, which was called philosophy. Philosophy-science is both like and unlike philosophy as we know it, and like and unlike science. It is like both of them because it encompasses the topics and questions of both science and philosophy. Philosophy-science asks questions about ontology and ethics. It also asks questions about the nature of the heavens and the origins of life. But this does not make philosophy-science philosophy or science any more than the shaman is the same as a doctor just because they both may offer opinions about what made a man sick. Philosophy-science is different than philosophy and science because it uses methods appropriate to one to address the questions of the other, and vice versa. It treats their questions and problems as amenable to the same sort of solutions. It treats philosophical questions as matters of fact that we can discover answers to, and it treats scientific questions as things that we can figure out by reasoning about them.
Both science and philosophy came out of philosophy-science, but science made out better because science was seen as breaking away from philosophy, rather than the other way around. The first scientists still were burdened by the legacy of philosophy-science and assumed that the world made rational sense, and thus that they could discover scientific truths by uncovering what was rational. This was science as Descartes pursued it. This was often bad science. Scientists eventually were able to move beyond this, in part because they saw themselves as breaking away from the tradition of philosophy-science. This gave them sanction to challenge the paradigm they found themselves in, and eventually to reject many of the ideas they inherited from philosophy-science about how their questions could be answered. Philosophers, unfortunately, did not find themselves in this position. They conceived of themselves as still doing the same sort of things the philosopher-scientists before them had done, minus a few topics and questions that the scientists had taken as their own (an ever-growing list, in actuality). Indeed this is how most modern philosophers read authors such as Aristotle and Descartes: they read the bits and pieces of them that have to do with philosophical issues, and largely ignore the pieces that have to deal with scientific ones. This is a strange way to read these authors. They certainly didn’t see themselves as engaging in two very different sorts of activities; they saw their work as a single continuous project that involved the same investigative skills applied to different topics. Is it not strange to pick out only pieces of their work as properly philosophical, and worth reading, when the authors themselves didn’t make that distinction? Why should their work be philosophically respectable and enlightening some of the time and irrelevant at others?
In any case, the long and short of it is that modern philosophers carry with them a legacy from philosophy-science that leads them to view every philosophical question as a scientific one (i.e. one where there is a discoverable matter of fact) and to apply methods to answering them that turned out to be next to useless when dealing with those same sorts of questions about different topics. Once what they are doing has been framed in this way it seems impossible that anyone could take it to be a good idea, although I must admit that I myself once subscribed to it. So, to return to ontology after this lengthy digression, the problem at the root of ontology that leads to those annoying questions discussed earlier is the assumption that ontology deals with some discoverable matter of fact. With that assumption questions along the lines of “how do you know?” are more than justified, and obviously answers that appeal to the ability of reason alone or some special insight will be unsatisfying, since reason alone/special insight isn’t any good elsewhere.
Solving ontology’s problems requires coming to understand it in a way that doesn’t presuppose ontology is seeking to uncover some matter of fact. Rather than taking ontology to be an act of discovery we can take it to be an act of creation. If ontology was art it wouldn’t be the kind that attempts to capture some existing scene on the canvas, but rather that which aims to create some new beauty that has never before existed. Admittedly this doesn’t say much about what ontology is about, it just opens up new possibilities. Here is my suggestion: ontology is a kind of metaphilosophy – ontology sets up a framework or structure for other philosophy to be done within.
Admittedly, even that isn’t saying much. To explain why we need ontology allow me to describe some fictitious philosophy. Suppose someone presented us with an ethical theory that explained why we shouldn’t harm other people by appealing to the fact that they are featherless upright bipeds with binocular vision. In one sense this theory fits the “facts”, it picks out human beings in general as a class that gets special moral treatment. But is it a satisfactory explanation? Of course not; properties such as “bipedal” simply aren’t philosophically or ethically significant. On the other hand properties such as “rational” are. If someone said that people deserved special ethical treatment because they had the capacity for reason we would take their proposal seriously, even if we disagreed. Deciding which properties are philosophically significant is the task, or at least one of the tasks, of ontology.
Of course no ontology consists of a giant list with every property, each marked as significant or not. That would be both absurd and impractical. Ontologies tend to deal with the big picture, and more specific matters are left to common sense. For example, it is common to divide properties from substances at the top level of an ontology. This can be taken to indicate two things. First that it is philosophically acceptable to appeal to the fact that something is a substance or a property to explain something about them. For example, you could say that a chair is in at most one place because it is a substance (versus a property, which can be in many places at one time). Secondly it describes what needs to be explained (or at least what is worth thinking about). The aforementioned ontology would be holding up substances and properties as in need of explanation, meaning that some philosopher should come up with a theory about the nature of substances, and that another should come up with a theory of properties. This of course goes hand in hand with the first point, since what you can explain by appeal to substance or property depends on what you think is always true of those categories.
This process can be iterated to get down to more specific issues, such as whether “bipedal” is admissible in a philosophical explanation. By iterated I mean that each of the categories of the ontology can be given their own ontology, and so on. For example, we might give an ontology of properties and divide them into the mental and non-mental. We might then give an ontology of mental properties and divide them into the intentional, the qualitative, and so on. Just as with the most general ontology, each time we do this we commit ourselves to the divisions being philosophically significant (i.e. a good thing to give philosophical explanations in terms of) and we hold each up as being worth of philosophical investigation (into their nature, i.e. “what is the nature of non-mental things (such that they are distinct from the mental)?”). Given the unpopularity of ontology philosophers rarely do this; and given that each sub-ontology is less significant than the one that came before it there is a point where it doesn’t make much sense to. However, I think that in doing philosophy we often end up committed implicitly to ontologies with metaphilosophical import, which finds an expression in our selection of topics and problems that we consider worth theorizing about and in the kind of theories we bother to consider.
Perhaps this view can be best summarized by saying that under it ontology becomes a lot like an agenda for philosophizing. The ontology describes a grand plan which describes both what is philosophically important and what future work needs to be done. Then the actual work of philosophy can get started, inspired and directed by this ontology, which aims to give a philosophical treatment to every item in the ontology. When everything was said and done and compiled into one very large book the ontology would be the table of contents. For every item there would be a corresponding chapter that described its nature and philosophical import. This analogy also suggests that the ontology might come last. After the book has been written then the author or editor goes back over it, organizing it and dividing it into sections. This doesn’t make ontology, so understood, any less a metaphilosophical project. Metaphilosophy can, and often does, come last, prompted by the desire to reflect on and understand what has come before.