ARE METAPHYSICAL DISCOVERIES POSSIBLE? IF SO, HOW?

Allow me to share with you one of my all-time favorite lines from a contemporary book on metaphysics: “Ontological discovery is not empirical. But ontologists1 do make discoveries. Or so say believers in ontology. And I believe. If seeing were believing, then by the end of this book you would believe too. For—assuming my arguments are successful—ontological discoveries follow.”2 I too am a believer in ontological discovery. And by the end of this chapter, I hope you’ll be a believer as well.

Initially, the idea of making ontological or metaphysical discoveries sounds strange to first-time philosophy students. When one talks or hears about “discoveries,” one no doubt thinks of empirical discoveries in particular, discoveries made with the help of the five senses of sight, touch, hearing, taste, and smell. There are many different ways of making empirical discoveries, some more or less complicated. Some empirical discoveries are made by simple inspection with the naked eye, as one might discover that it rained last night simply by looking out the window, or how one might discover the best restaurants in one’s new city of residence by tasting their respective cuisines. Discovering the sum total of one’s liquid assets, by contrast, involves a more careful, empirical investigation, while William Gilbert’s discovery of electricity in the seventeenth century involves a great deal more effort, inquiry, and sacrifice.

But what exactly are we to make of the traditional claim, explored in the previous chapter, that the study of metaphysics can yield genuine, albeit nonempirical, discoveries? What kinds of discoveries could there possibly be other than those that are made by way of empirical observation? It turns out that many philosophers in the early and mid-twentieth century were uneasy, even openly critical of the idea of making genuine discoveries about reality apart from sensory experience. It is important to first note that well into the twentieth century many influential philosophers, driven mainly by a view that restricts the scope of knowledge to what is sensory or empirical (“empiricism”), would have scoffed at the idea of nonempirical discovery (at least the kind that is informative, i.e., not trivially true or true by definition). We will look at this historically prominent objection to metaphysics in due course in this chapter.

For starters, why think empirical discoveries are the only kinds of discoveries that can be made? What, exactly, is the argument supposed to be here? To help initially open up space for the tenability of the idea of nonempirical discovery, and thus for genuine metaphysical discovery, we need to consider the following crucial question: Is the claim that empirical discovery is the only kind of discovery possible itself an empirical discovery? Did some fine-grained scientific instrument or sensory observation reveal this particular truth about the nature and scope of the types of discoveries that are possible? Does someone just “look and see” that this is true? Well, of course not. So, even at the outset, it is clear that while empirical discoveries are indeed important and make up our knowledge of one particular aspect of reality—namely the material world, the aspects of reality that exist in a sense-perceptible way—they certainly are not (cannot be!) the only kinds of discovery possible. And this is very good news for metaphysics!

What if there is such a thing as nonempirical discovery about reality, discovery that is not secured by the five senses but by rational insight alone? Historically, metaphysical discoveries about the nature and structure of being are made by way of pure rational insight. Here I want to defend the idea of metaphysical discovery and shore up the intellectual credentials of the discipline of metaphysics. First, I will briefly unpack the nature of rational insight itself. I’ll then interact with a few well-known historical and contemporary objections to the intellectual credentials of metaphysics, namely, the idea that rational insight alone cannot reliably yield informative, nonempirical discoveries about reality.

Traditionally, metaphysical inquiry has been concerned with metaphysical knowledge. Going forward, I’ll work with an informal characterization of knowledge as roughly the ability to represent reality as it is on the basis of adequate grounds.3

We commonly take ourselves to have knowledge in this sense about many mundane areas of life: I know that there is a coffee mug on the desk (perceptual knowledge), that 2+2=4 (mathematical knowledge), that electrons have negative charge (scientific knowledge), that there was an American Civil War and that Southeastern Seminary was founded in 1950 (historical knowledge), and so on. When I claim to know a matter of history or science, like there was an American Civil War or that electrons have negative charge, I claim to have the ability to represent the past and the physical world as they actually are (were), on the basis of some good reason or other. But what sort of adequate grounds or good reasons might legitimate these claims of historical and scientific knowledge? At least for most of us, when it comes to both historical and scientific knowledge in particular, it is pretty clearly the case that these claims to knowledge are supported by reliable testimony; I rightly claim to know (as opposed to merely believing them without adequate reasons) these historical and scientific matters precisely because I have it on reliable authority that there was a Civil War, or that electrons exist and have negative charge.

Claims to metaphysical knowledge, understood in this sense, should also be supported by adequate grounds or good reasons. Yet, the adequate grounds or reasons that have traditionally played a role in legitimizing metaphysical beliefs (“God exists,” “human souls exist and are immaterial,” “free will exists,” etc.) are very different from grounds commonly thought to support ordinary beliefs about the physical world. From a Christian perspective, metaphysical knowledge—knowledge about the fundamental contour of reality—is available to us (at least in principle) both by virtue of our God-given intellectual capacities for rational thought and by way of divine testimony in Scripture.4 In this way, metaphysics aims at genuine, nonempirical knowledge of reality, either by way of pure rational insight or by divine testimony. But what is this idea of knowledge by way of pure rational insight alone, apart from our sensory experience of the world?

Philosophers throughout the Western tradition have commonly distinguished between two different ways of knowing a particular proposition or statement. Consider the following statements that one might claim to know to be true:

When we carefully consider statements like (a)-(i), we are struck by the fact that they each seem to have something going for them epistemically; that is, they strike us as not only psychologically compelling but also as reasonably true and well supported on consideration. When a belief is reasonably well supported in this sense, when it is based on adequate grounds or evidence, the belief is what philosophers call “epistemically justified.” The belief is above board intellectually, so to speak. What adequate grounds, we might ask, epistemically justify statements (a)-(i)?

I think it is reasonably clear that some of the above statements, such as (a)-(d), are epistemically justified by way of our sensory experience of the world; they are known in an a posteriori manner (a manner that is based on one’s sense experience of the world), as philosophers like to say. Others, such as (e)-(i), are epistemically justified apart from sensory experience by way of rational insight alone; we can just intellectually “see” or “perceive” that they are true on thoughtful inspection. Statements such as (e)-(i) that are arguably known prior to or independent of sensory experience are thus known in an a priori manner, by simply thinking and reflecting on them. When we intellectually reflect on (e) and (h) in particular, a truth of arithmetic and logic respectively, they immediately strike us as being worthy of belief in that they are quite reasonable and epistemically justified. Or consider (i), that I cannot be identical to a turnip. When I reflect on what I am (a human person) and what a turnip is (a type of edible root), I see by the light of reason that it is impossible for me to be one and the same thing as an edible root; my nature, what I am essentially, seems to rationally preclude my being one and the same thing as a turnip. I think Aristotle was right when he said that thought is a bit like perception: “Thinking and understanding are regarded as akin to a form of perceiving; for in the one as well as the other the soul discriminates and is cognizant of something which is.”5

Let me quickly clear up a common misunderstanding of nonempirical, a priori knowledge at this point. As Alvin Plantinga helpfully points out, the idea of a priori knowledge...