What is Naturalism? Part II: Kant’s Phenomenal/Noumenal Distinction

In my previous post I started a series in which I hope to shed some light on the distinction between "metaphysical naturalism" and contrary ontological positions. I began there with an overview of the position I want to develop. Today, I want to look more closely at a key distinction that I will make use of throughout this series—specifically, Kant’s distinction between phenomena and noumena.

For Kant, the “phenomenon” refers to the object of experience—or, perhaps better, the object as experienced. The “noumenon” refers to the thing as it is in itself. Thus, there is for Kant the phenomenal or empirical world, which will inevitably be constituted in part by the faculties we rely on to interact with the underlying reality; and then there is the noumenal world— reality “as it truly is in itself,” we might say, apart from our experience of and cognitive engagement with it. In oversimplified terms, what we have here is the distinction between appearance and reality.


Kant makes several important points with respect to this distinction in The Critique of Pure Reason. First, the phenomenon is the object as given to us in sense perception, or through what Kant also refers to as an “empirical/sensible intuition” (for Kant, to “intuit” something is to be, in a sense, presented with it through some faculty of apprehension; and empirical intuition is contrasted with the kind of apprehension we have of mathematical objects, which Kant calls a “pure intuition”).

Second, sense perception or “empirical intuition” presents objects to us in a certain form—specifically, phenomena always come to us as situated in space and time. But this, Kant argues, is a feature of our sensory faculties, not a feature of things in themselves. In Kant’s words, “space and time are only forms of sensible intuition, therefore conditions of the existence of things as appearances only.” Put another way, our perceptual faculties are designed so as to spontaneously organize sensory inputs in spatio-temporal terms, so that the phenomenal objects given to us through perception are always located in space and time. But it doesn’t follow from this that spatio-temporal location is a feature of noumena, that is, of objects as they are in themselves.

As Kant puts it, “…space is nothing if we leave out of consideration the condition of all possible experience, and assume it as something on which things in themselves are in any way dependent.” That is, space is meaningful only as attributed to the world as it appears to us (the phenomenal world), not when it is attributed to the world as it is in itself.

Third, humans are not merely awash in a sea of sensory experience. We aren’t just presented with phenomenal objects. We also think about them. We make judgments about them and can come to know things about them. And this requires concepts. One of Kant’s most important ideas is that there are certain basic laws by which human cognition operates. More specifically, our minds have these basic concepts or “categories of the understanding” by which we make sense of “intuitions”—and it is only through the work of these categories (which include the categories of cause and effect, by the way) that we can formulate propositions about the phenomenal objects we intuit.

Let’s put it this way: when we passively experience the “external” world, what comes to us immediately is already merely an “appearance” rather than the thing in itself. But as human beings, we rarely just experience the world passively—and whenever we try to do something more (whenever we form beliefs about the world) we do so in terms of conceptual categories that are a part of our cognitive make-up rather than part of reality “in itself.” This means that the object of the understanding—the object as something we can have beliefs about, learn things about, etc.—is in a sense even further removed from the noumenon, the “thing as it is in itself,” than is the uncomprehended phenomenal object (what we might suppose is experienced by the newborn baby).

For these reasons Kant draws a very sharp line between the world of phenomenal objects that we can study and learn things about and the world of things-in-themselves (the noumenal world). In fact, Kant was convinced that our knowledge could never reach beyond the realm of phenomena. He thought we could confidently say there is a noumenal reality, a thing in itself, that isn’t identical with the phenomenal object we directly encounter in experience. While he’s convinced that “all theoretical knowledge of reason is limited to objects of experience,” that is, to phenomenal objects as presented by intuition and conceptualized by our cognition, he also thinks “that this leaves perfectly open to us to think the same objects as things in themselves, though we cannot know them. For otherwise we should arrive at the absurd conclusion that there is appearance without something that appears.”

So, in summary: we can know that there are things-in-themselves or noumena, we cannot know anything about them. The objects of perception are already shaped by the process of being perceived, and are further shaped by the conceptual categories we must make use of in order to even begin to formulate knowledge claims. The objects of our knowledge are therefore necessarily, inescapably, objects that we have helped to construct through our sensory and cognitive apparatuses. Things as they are in themselves are thus utterly unknowable.

This doesn’t mean we can’t postulate things about noumena. In fact, Kant thought we had to do so. He was convinced that making sense of ourselves as moral agents requires us to make postulates about the noumenal realm (especially about the noumenal self—me as I am in myself as opposed to me as the object of my experience). But these postulates are just that. They are not knowledge. Knowledge of the noumenal is impossible.

If you take Kant seriously about all of this, then his perspective has some very important implications. One is this: whatever scientists discover, through whatever methodologies they employ, will never be an understanding of reality itself. At best, science will be the project of describing in painstaking detail the world of appearances (what Kant called the empirical world) and constructing helpful conceptual models for engaging with it in ways that, we might say, decrease the frequency with which we are surprised.

Predictably, many scientists have historically been loath to accept this implication—as have philosophers and theologians. Scholars in various disciplines have sought to pierce the wall of mystery that Kant erected—some by defending a “direct realism” which denies the phenomenal/noumenal distinction, others by acknowledging the distinction but looking for some method of inquiry that can take us through the wall into the noumenal world. Ultimately, I think metaphysical naturalism is a claim to the effect that scientists have found a way to pierce that wall—that, in other words, what they are modeling for us on the basis of their methodologies isn’t just a useful way to engage with the phenomenal world but is, actually, a picture of reality as it is in itself.

As such, metaphysical naturalists are in the same camp as others—such as Hegel and Schleiermacher—who have been unwilling to accept that the veil between us and noumenal reality is utterly impenetrable. But they are looking in a very different place for the way to peek beyond the veil.

But these last points are ones I will develop in my next post in the series.