---
title: "Materialism controversy"
chunk: 4/6
source: "https://en.wikipedia.org/wiki/Materialism_controversy"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T04:18:03.001865+00:00"
instance: "kb-cron"
---

== Reactions in the 19th century ==

=== Philosophy of neo-Kantianism ===
Materialism, as promoted by scientists like Carl Vogt, Jakob Moleschott, and Ludwig Büchner, was presented as a direct consequence of empirical scientific research. Following the decline of German idealism, many saw academic philosophy—especially as taught in universities—as disconnected from reality and reduced to speculative thought. Even philosopher Ludwig Feuerbach, once aligned with idealist traditions, placed his trust in the natural sciences to answer longstanding philosophical questions such as the relationship between body and soul.
However, a strong philosophical critique of materialism did not emerge until the 1860s, with the rise of Neo-Kantianism. In 1865, Otto Liebmann published Kant und die Epigonen (Kant and His Followers), a work that sharply criticized major post-Kantian thinkers—from German idealists to Arthur Schopenhauer. Liebmann famously ended each chapter with the refrain: "So we must go back to Kant!". The following year,Friedrich Albert Lange published Geschichte des Materialismus (History of Materialism), in which he aligned himself with the Neo-Kantian position. Lange accused the scientific materialists of “philosophical dilettantism”, claiming that they overlooked central insights of Kantian thought.
At the core of Kant’s philosophy, particularly in the Critique of Pure Reason, is the question: What are the conditions for the possibility of knowledge? Kant argued that human beings do not perceive the world as it truly is, but rather through cognitive structures shaped by the mind. Concepts such as cause and effect, unity, and multiplicity are not features of the external world itself but mental categories we impose on our experiences. Similarly, space and time are not absolute properties of reality but forms of human perception. Since all experience is already filtered through these mental structures, Kant concluded that we can never know things-in-themselves—that is, reality as it exists independently of human perception. As a result, Kant held that it is impossible to scientifically prove or disprove the existence of free will, a personal God, or an immaterial soul. These ideas lie outside the scope of empirical investigation.
Friedrich Albert Lange used Kant’s theory to argue that materialism made a fundamental mistake: it claimed that only matter exists, but failed to recognize that even scientific descriptions of matter are shaped by human perception. Therefore, science cannot claim to describe absolute reality; it only describes how reality appears to us through our cognitive framework. This argument was supported by physicist and physiologist Hermann von Helmholtz, who had studied the physiology of perception in the 1850s. In his 1855 lecture, Über das Sehen des Menschen (On Human Vision), Helmholtz explained that vision does not offer a faithful copy of the external world. Instead, visual perception is constructed by the brain based on incomplete sensory input. Helmholtz’s work echoed Kant’s view: every act of perception involves interpretation, and this interpretation is shaped by human cognitive faculties. Because of this, direct access to objective reality—the “thing-in-itself”—is not possible.

=== Ignoramus et ignorabimus ===

The scientific materialists did not engage with the arguments of the Neo-Kantians, as they saw the reference to Kant as just another speculative attack on the results of the natural sciences. A more serious challenge came from Emil Heinrich Du Bois-Reymond, a prominent physiologist, whose 1872 lecture Über die Grenzen des Naturerkennens (On the Limits of Understanding Nature) posed a direct challenge to the foundations of materialist thought. In this lecture, Du Bois-Reymond famously declared that certain aspects of nature, particularly consciousness, would always remain beyond scientific explanation. He summed this up with the Latin phrase: "Ignoramus et ignorabimus" (Latin for "We do not know and we will never know"). This statement sparked the Ignorabimus controversy, a long-running public and scientific debate over whether science could ever fully explain the human mind and consciousness. The intensity of the debate rivalled—and in some circles exceeded—that of the earlier Vogt–Wagner controversy of the 1850s. However, by this point, materialists found themselves increasingly on the defensive.
Du Bois-Reymond criticized the materialist position for failing to explain how consciousness arises from the physical processes of the brain. While Vogt, Moleschott, and Büchner pointed to the observable dependence of mental functions on brain activity—especially demonstrated through brain injuries and animal experiments—this, he argued, did not address the deeper issue. However, for Du Bois-Reymond, this approach was insufficient. He argued that demonstrating a correlation between brain activity and mental states does not explain why or how subjective experience—pain, desire, colors, sounds, and so on—emerges from physical processes.
Du Bois-Reymond concluded that there was no intelligible link between the objective facts of physics and the subjective nature of conscious experience. As such, consciousness represented a fundamental limit to what science could explain. 
The Ignorabimus speech revealed a major weakness in the materialist worldview. While the materialists insisted that consciousness was a product of the brain, they conceded that science could not yet—and might never—explain it. This gap contributed to a broader shift in the scientific worldview during the late 19th century, from strict materialism to monism. Ernst Haeckel, one of the most influential scientists of the time, became the leading advocate of this monistic worldview. Like the materialists, he rejected dualism, idealism, and the immortal soul, but he also moved away from the materialist claim that only matter was real.
Unlike materialism, monism held that mind and matter were equally fundamental and inseparable aspects of a single underlying reality. In this way, spirit was no longer something that had to be explained in terms of matter alone, potentially resolving the issue raised by Du Bois-Reymond.