Today I’m looking at Immanuel Kant’s “thing-in-itself” and Hans Vaihinger’s ideas. In Kant’s philosophy, the thing-in-itself (Ding an sich) refers to the reality that exists independently of human perception or experience. Kant argued that while we can know phenomena (i.e., the appearances of things as they present themselves to us), the thing-in-itself remains inaccessible to human cognition. Our knowledge is always mediated by the structures of our mind (such as space, time, and categories of understanding).

The Kantian dichotomy therefore is phenomena (i.e., things as they appear to us) and the noumena (the things-in-themselves). For Kant, the thing-in-itself is something that exists independently of human perception but is forever inaccessible to us. We can only know the world as it appears to us, not as it truly is in itself. This creates a separation between appearance and reality, and Kant suggests that this gap is unbridgeable for human beings.

I’m not a fan of dichotomies. Most often, dichotomies are created as linguistic tools to aid our thinking. But they form a life of their own and can also cause confusion in our thinking.

There are a few ways to think about the thing-in-itself. One is to take the road that reality is indeed accessible to us. This will be the approach of a naive realist. This notion can be easily disproven using numerous illusions. The second route is to be an idealist. Loosely put, this approach takes the view that everything is in the mind. This notion is also not very useful. And it’s another dichotomy: Reality is directly accessible out there vs. reality is all inside our minds.

It’s more useful to take a middle path. Here also, there are different ways to go. One example is Charles Sanders Peirce, a realist American philosopher. He believed that reality exists out there independent of our perception. We might not have direct access to it, but we can gradually make sense of it. He believed that all knowledge is fallible and subject to revision. Instead of positing an unknowable reality, he focused on the continuous process of inquiry and the gradual approximation of truth. In this view, the notion of the thing-in-itself is not value-adding since Peirce is proposing that reality, or portions of reality, are eventually accessible to us.

Peirce was a pragmatist (or a pragmaticist as he called himself). As noted above, pragmaticism supports the idea of truth. If there’s a practical or pragmatic observable effect, then that becomes truthful. Truth in this case isn’t absolute because pragmatists support the idea of fallibilism—that truth is provisional. What we’ve discussed so far moves toward the realist camp.

It’s here that I want to introduce the ideas of Hans Vaihinger. I side with his ideas. Vaihinger was a German philosopher who studied Kant vigorously. His ideas have many familiarities with pragmatism. He proposed the philosophy of “as-if.” He came up with the notion of “useful fictions” instead of “truth” in pragmatism. Similar to pragmatism, Vaihinger’s thinking focused on practical applications in the world. He argued that the thing-in-itself isn’t something we can know, but that it functions as a “useful fiction” that helps guide our thinking and practical action. According to Vaihinger, we can use the concept of the thing-in-itself as a heuristic tool, a fiction that helps us organize our experience and navigate the world, even though it doesn’t correspond to anything directly accessible to human cognition.

In a sense, Vaihinger suggests that the thing-in-itself has practical utility, even if it’s ultimately unknowable. It provides a framework for understanding reality, even if that framework isn’t literally true. For Vaihinger, this “fiction” is necessary for guiding human action and thought, even if it is not an accurate representation of an objective reality. He is not interested in “truth.” Unlike the pragmatists, he calls his ideas fictions.

Vaihinger discussed his ideas in his magnum book The Philosophy of As-If. (Routledge, second edition 2021). He argues that human thought, fundamentally, is geared not toward metaphysical truth or solving abstract problems but toward survival and fulfilling the “life-will” (Arthur Schopenhauer’s term for the fundamental drive to live and survive). This perspective leads Vaihinger to conclude that human cognitive faculties are inherently limited, not because they’re defective but because they evolved for specific, practical, and existential purposes: to help humans navigate the world and satisfy their basic needs.

Vaihinger views human thought as essentially a tool for life, serving the practical ends of survival rather than speculative exploration of ultimate reality. Human cognition wasn’t designed to uncover metaphysical truths or answer the “big questions” about the nature of the universe. Instead, it evolved as a means to manage and react to immediate environmental challenges—finding food, avoiding danger, securing shelter, reproducing, and so on. From this perspective, thought is a functional tool, not a quest for objective knowledge.

In this way, Vaihinger agrees with Kant that human knowledge is bound by certain limits. But Vaihinger takes Kant’s idea further: Instead of viewing these limits as a tragic deficiency (i.e., the inability to access noumena or things-in-themselves), Vaihinger argues that they are the natural result of human thought’s biological and practical function. Thought was never intended to grasp the ultimate nature of reality; it evolved to solve problems relevant to human survival and everyday life.

Given that human thought is limited in this way, Vaihinger proposes that we use certain concepts—like the thing-in-itself—as fictions. These fictions aren’t intended to describe the ultimate nature of reality but to help us organize and navigate our experience of the world. The thing-in-itself, as a fiction, becomes a useful tool for thought, enabling us to conceptualize reality in a way that facilitates practical action and understanding, even if that concept doesn’t correspond to anything we can directly know or experience.

Vaihinger argues that these fictions are essential because they allow us to deal with phenomena that can’t be grasped directly. The thing-in-itself becomes a placeholder or a symbolic construct that helps us maintain coherence in our thinking and practical activities, even though it doesn’t correspond to any knowable “reality.” In this way, Vaihinger’s approach offers a way to work with limitations in thought while still reasoning, acting, and engaging with the world meaningfully. Similar to Peirce, Vaihinger maintained that all knowledge is fallible and provisional. He also emphasized the idea of correcting ideas when they are no longer viable.

The paradox of thing-in-itself

The notion of the thing-in-itself comes with a paradox. If the thing-in-itself isn’t accessible to us, then how can we even talk about it? How can we ascertain that what we experience is supposed to represent the thing-in-itself? The very act of trying to access the thing-in-itself proves its inaccessibility. Kant acknowledged the limits of human cognition and left us with the concept of the thing-in-itself to indicate that reality exists beyond our perception. Kant insisted that we can’t know the thing-in-itself because our mind imposes its own structures onto the world. So, the thing-in-itself is something that remains, by definition, unknowable. We humans are separated from the “true” nature of things.

Let’s use an example to make things clearer. Imagine the reality of a landscape. Kant originally suggested this is a reality we can’t directly touch; it’s as if the landscape is behind a thick fog. We can see outlines, but not the detailed terrain itself.

Peirce proposed that we have multiple ways to understand that landscape, such as signs, instruments, and mathematical models. It’s not that the landscape is unknowable, but that we approach it through creative interpretation. These are not just representations; they are active ways of constructing understanding. Instead of seeing the thing-in-itself as an impenetrable mystery, Peirce suggests it’s more like a dynamic puzzle. We don’t give up because we can’t see the whole picture immediately. We use every tool we have—mathematical models, technological instruments, logical reasoning—to progressively understand. Peirce claimed we can access reality through signs and mediation.

If we look at Vaihinger’s ideas, he would call Peirce’s signs still fictions that we’ve constructed. The mathematical models, instruments, and interpretive frameworks are themselves useful fictions that help us navigate experience.

The key distinction between Peirce and Vaihinger is that Peirce believed that we are progressively accessing reality, and Vaihinger saw us as creating increasingly sophisticated, but still fundamentally fictional, frameworks of understanding. Using our example, it’s like different ways of mapping an unknown territory. Peirce is thinking that we’re gradually revealing the actual landscape. Vaihinger is saying that we’re creating ever-more-useful maps, knowing that they’re not the territory itself.

In my opinion, there’s a noumenal gap that realism can’t transcend. No matter how sophisticated our signs, instruments, or mediations, we can’t escape the fundamental epistemological limitation. Our cognitive apparatus always interprets, always mediates, always transforms. Any “progress” is still within our conceptual framework. We’re not getting closer to the thing-in-itself. We’re often simply creating more complex interpretive structures.

Vaihinger’s idea that the thing-in-itself is a “useful fiction” suggests a different way of thinking. He argues that although we may never have direct access to the thing-in-itself (or any ultimate reality), the concept of the thing-in-itself can still be useful for organizing experience and guiding practical action. According to Vaihinger, the idea of the thing-in-itself is a fiction, but one that’s necessary for making sense of the world. It’s a construct that helps us navigate and interact with our experiences, even if it doesn’t correspond to any objective reality beyond our conceptual framework.

Vaihinger’s view allows us to maintain the utility of concepts like the thing-in-itself without being trapped in the idea that they correspond to something inaccessible in a metaphysical sense. For Vaihinger, the thing-in-itself isn’t some unreachable essence, but a concept that functions within human thought in a way that allows us to make sense of the world. It’s a fiction that helps us act and think meaningfully, even though we know it doesn’t correspond to something we can access directly.

This is a much more flexible and practical stance than that taken by Kant or Peirce, because it allows for the continued use of concepts like the thing-in-itself without needing to assert that they refer to an objective, inaccessible reality. Instead, we can use them for practical reasoning, action, and understanding, while acknowledging their fictional status.

Vaihinger moves beyond the notion that we’re limited by a distance from ultimate reality and suggests that the limitations of our understanding don’t prevent us from using concepts that guide our actions. He doesn’t need to answer whether we can access the thing-in-itself in any literal sense because he acknowledges that it’s a fiction—yet a necessary one. Vaihinger provides a path forward in that sense. We no longer need to grapple with the unknowability of ultimate reality but instead can work with useful fictions that help us navigate the world. This gives us a much more flexible, nondogmatic framework for understanding our place in the world and how we think about things like the thing-in-itself.

If we ask for the burden of proof for the various ideas we’ve discussed here, we see that both realism and idealism carry a significant burden of proof because they are making claims. Even with Peirce, there’s a significant burden of proof. He must still prove that signs can access reality. Vaihinger, on the other hand, avoids any metaphysical commitments. By treating the thing-in-itself as a useful fiction, he sidesteps the burden of proof altogether. His focus is only on the viability of an idea.

I’ll finish with a quote from Vaihinger: “The world of ideas... we generally call ‘truth’ is consequently only the most expedient error, i.e., that system of ideas which enables us to act and to deal with things most rapidly, neatly, and safely, and with a minimum of irrational elements.”

Note: There are, of course, numerous other schools of philosophy, such as critical realism, radical constructivism, etc., that I haven’t looked at here.

Published Jan. 26, 2025, in Harish’s Notebook.