Qualia are the most obvious thing in existence — and at the same time that at which every materialist explanation of the world founders. The taste of coffee. The redness of red. The sting of a pain. Every human being knows these qualities immediately; everyone knows what it is like to experience something. And yet no natural science can explain why there is any experience at all.
#The Word and the Concept
The Latin plural qualia — “of what kind, of what character” — established itself as a philosophical term in the twentieth century. C.I. Lewis introduced it in 1929, but the matter itself is older than its name. What is meant is the subjective experiential quality of conscious experience: not the wavelength of 700 nanometres registered by an instrument, but the red that someone sees. Not the activation of nociceptors, but the pain that someone feels. Qualia denote the inner dimension of experience, the what-it-is-like — that aspect of reality which reveals itself as soon as a being does not merely function but experiences.
#Nagel’s Bat and the Explanatory Gap
Thomas Nagel posed a question in 1974 that has not fallen silent since: “What is it like to be a bat?” (Nagel, 1974). Bats orient themselves through echolocation — a mode of perception that humans do not possess. One can describe the bat’s neurobiology completely, map every nerve impulse, measure every frequency. And one still does not know what it feels like for the bat to fly through the night by sonar. This ignorance is not a provisional deficit that better instruments could remedy. It is principled: the third-person perspective of science cannot catch up with the first-person perspective of experience.
David Chalmers formulated from this the Hard Problem of Consciousness in 1995: Why does neural processing produce subjective experience? One can explain how the brain processes information, how it responds to stimuli, how it governs behaviour — these are the so-called easy problems. The question of why it feels like something for someone in the process belongs to another category. It cannot be answered by more data, because the data themselves are couched in the wrong language (Chalmers, 1995).
#Nietzsche: Quality as an Insurmountable Barrier
More than a hundred years before Chalmers, Nietzsche recognised the core of the problem with a clarity rarely acknowledged in the contemporary debate:
Natural science describes quantities — wavelengths, frequency patterns, neural firing rates. What it cannot describe is the qualitative character of experience that attaches to these quantities. “Our knowledge is limited to establishing quantities; but we can by no means prevent ourselves from feeling these differences of quantity as qualities” (Nietzsche, The Will to Power, §396). Experience itself remains beyond the reach of measurement — not from technical inadequacy but for structural reasons.
#What Reduction Conceals
The standard strategies for dissolving qualia fail in characteristic ways. Eliminativism claims that subjective experience does not exist at all — a position that cancels itself, since the eliminativist consciously experiences their own claim while denying consciousness. Functionalism declares qualia identical with functional states — but two functionally identical systems can “feel” qualitatively different, or one may not feel at all. Epiphenomenalism concedes qualia but declares them causally inert — an assertion that suggests the theory does not take the explanandum seriously.
Every attempt to explain qualia in purely physical terms eventually changes the subject: it describes the neural conditions of experience rather than experience itself. What is lost in the process is precisely what was supposed to be explained.
#Qualia and the Question of the Machine
The qualia problem has an immediate consequence for the question of whether machines can be conscious. If subjective experience cannot be derived from functional organisation, then even the most complex computation cannot produce experience. A computer can classify red without seeing red. It can process pain signals without suffering. What is missing is the inside — that dimension Jochen Kirchhoff describes as constitutive of everything living: the human being has emotions, thinks about things, is happy or unhappy — the motion of physics is dead, mathematics too is dead, but the human being is not (cf. Kirchhoff, J., 2023, AI and Transhumanism as a Threat to the Living).
In natural philosophy, what appears here is the limit of the mechanistic analogy. Whoever takes the machine as a model for understanding the cosmos has already defined qualia away before beginning to explain. One operates, as Gwendolin Kirchhoff put it in the Everlast debate of 2026, with a metaphysics that “produces a Hard Problem and a Boot Problem and cannot solve them.”
#The Natural-Philosophical Perspective
From the standpoint of natural philosophy, qualia are neither riddle nor anomaly but testimony. They testify that reality possesses an inner dimension that cannot be reduced to outer description. Schelling captured this in 1797 in a formula that resolves the qualia problem avant la lettre: so long as I myself am identical with nature, I understand what living nature is as well as I understand my own life (cf. Schelling, 1797, Ideas for a Philosophy of Nature). Subjective experience is not something that mysteriously accrues to matter. It is the primary way in which reality is given to itself.
The materialist premise — that matter is primary and consciousness derivative — is, as Jochen Kirchhoff argues, “bad metaphysics”: a metaphysical decision that passes itself off as empirical self-evidence (Kirchhoff, J., 1998). Qualia do not refute this premise by means of an argument but by their sheer existence. Every moment of conscious experience demonstrates that the world possesses a qualitative dimension that precedes quantitative description.
Arthur Schopenhauer had already seen this point: the forms of our perception are “of entirely subjective origin” — they are “the mode and manner of our faculty of intuition” (Schopenhauer, 1844, The World as Will and Representation II). What natural science describes as the objective external world is always already mediated through the subjective experience of a being. Qualia do not stand at the end of an explanatory chain; they stand at its beginning.
#Sources
Chalmers, D. (1995). “Facing Up to the Problem of Consciousness.” Journal of Consciousness Studies, 2(3), 200-219.
Kirchhoff, J. (1998). Was kostet die Welt? — Vom Preis und Wert des Lebendigen. Engel & Co.
Kirchhoff, J. (2023). KI und Transhumanismus als Bedrohung des Lebendigen [Video]. Jochen Kirchhoff — In Memoriam, YouTube.
Nagel, T. (1974). “What Is It Like to Be a Bat?” The Philosophical Review, 83(4), 435-450.
Nietzsche, F. (1901/posthumous). Der Wille zur Macht. Kroner.
Schelling, F.W.J. (1797). Ideen zu einer Philosophie der Natur. Breitkopf und Hartel.
Schopenhauer, A. (1844). Die Welt als Wille und Vorstellung, Second Volume. Brockhaus.
Related entries: Philosophy of Consciousness, Natural Philosophy, Raumorgan, Consciousness and AI, The Mind-Body Problem