Materialism controversy
The materialism controversy was a public debate in the mid-19th century about how new developments in the natural sciences might affect existing worldviews. During the 1840s, a new form of materialism emerged, shaped by advances in biology and the decline of idealistic philosophy. This form of materialism sought to explain human beings and their behavior through scientific methods. The central question of the debate was whether scientific discoveries were compatible with traditional ideas such as the existence of an immaterial soul, a personal God, and human free will. The discussion also touched on deeper philosophical issues, such as what kind of knowledge a materialist or mechanical view of the world could offer.
In his Physiologische Briefe from 1846, zoologist Carl Vogt argued that mental processes were entirely physical, famously stating that "thoughts stand in the same relation to the brain as bile does to the liver or urine to the kidneys." In 1854, the physiologist Rudolf Wagner criticized this view in a speech to the Göttingen Naturalists' Assembly. He argued that religious belief and science belonged to separate areas of understanding, and that natural science could not answer questions about God, the soul, or free will.
Wagner’s comments were strongly worded, accusing materialists of trying to undermine spiritual values. His attacks sparked sharp responses from Vogt and others. The materialist position was later defended by figures such as physiologist Jakob Moleschott and physician Ludwig Büchner, brother of writer Georg Büchner. Supporters of materialism saw themselves as opposing what they viewed as outdated philosophical, religious, and political ideas. While their approaches varied, they found growing support among the middle classes. The idea of a scientific worldview became an important feature in the broader cultural debates of the late 19th and early 20th centuries.
Development of natural scientific materialism
Emancipation of biology
The rise of popular materialism in the mid-19th century was partly driven by growing criticism of romantic and idealist natural philosophy. This critique became widespread after 1830 and influenced science, philosophy, and politics alike.One major scientific development that supported this shift was the emergence of cell theory, founded by botanist Matthias Jacob Schleiden. In 1838, Schleiden published a study on plant development in which he identified the cell as the basic unit of all plant life and emphasized the role of the cell nucleus, discovered in 1831, in plant growth. This theory marked a turning point in botany, which had previously focused mainly on describing the external forms of plants. Schleiden combined his scientific findings with a strong critique of idealist natural philosophy. He argued that scientific knowledge must be based on direct observation, unlike the speculative systems of earlier philosophers. According to him, abstract theorizing not grounded in evidence had to be rejected.
Schleiden’s call for a more scientific and observation-based approach soon influenced other areas of biology. In 1839, Theodor Schwann published Microscopic Investigations on the Similarity in Structure and Growth of Animals and Plants, extending Schleiden’s ideas to animals. Schwann proposed that all living things are made of cells and that tissues and organs develop through cell growth and reproduction. Building on this, physician Rudolf Virchow later summarized the idea by stating: “Life is essentially cellular activity". These insights laid the foundation for a scientific understanding of life, which materialist thinkers would build upon in the following years.
Turning away from idealistic philosophy
At the same time, a broader critique of German idealism began to take shape, especially in the years before the 1848 revolutions . While many scientists still opposed materialism, criticism of idealist philosophy became more common, particularly among younger intellectuals.One of the most influential figures in this movement was Ludwig Feuerbach, whose 1841 work The Essence of Christianity'' had a major impact. Feuerbach had studied under Georg Wilhelm Friedrich Hegel in Berlin and initially followed the idealist tradition. However, by the late 1830s, he began to reject it. Like other young Hegelians, he grew dissatisfied with idealism's abstract systems and its alignment with conservative politics. In 1839, Feuerbach openly criticized Hegel's philosophy. While he acknowledged its internal logic, he argued it was too far removed from the natural world and human experience. Feuerbach believed that philosophy should be grounded in the senses and in the physical reality of nature and humanity. As he put it: “All speculation that seeks to go beyond nature and man is vain. Although Feuerbach was not a scientist, his ideas about grounding knowledge in human experience and nature echoed the goals of the new biology. He promoted a type of anthropology—a theory of humanity based on lived experience—rather than a speculative or purely scientific approach.
Feuerbach’s most controversial ideas came from his critique of religion. He argued that religion was not a reflection of divine truth, but a projection of human hopes and needs. God, he claimed, was not an external being, but a creation of the human mind. While he did not reject religion entirely, he believed its value lay in its psychological and emotional function, not in metaphysical truth. Religious doctrines, he argued, could not be proven through reason or science—they were, in his view, products of imagination rather than reality.
Carl Vogt and the political opposition
The materialism controversy was sparked in part by the writings of physiologist Carl Vogt, beginning in 1847. His commitment to materialism was shaped by the scientific and political reform movements of the time, as well as his own personal and political development. Vogt was born in Giessen in 1817, into a family with both scientific and revolutionary traditions. His father, Philipp Friedrich Wilhelm Vogt, was a professor of medicine who moved to Bern in 1834 after facing political persecution. On his mother’s side, political activism was also a strong influence: Louise Follen’s three brothers—Adolf, Karl, and Paul Follen—were all involved in nationalist and democratic causes and eventually went into exile.In 1817 Adolf Follen drafted a proposal for a future German constitution and was later arrested for his political activities. He avoided a 10-year prison sentence by fleeing to Switzerland. Karl Follen was suspected of encouraging the assassination of conservative writer August von Kotzebue and escaped to the United States, where he became a professor at Harvard University. The youngest brother, Paul Follen, helped found the Gießener Auswanderungsgesellschaft in 1833, which aimed to establish a German republic in the U.S. Though the plan failed, Paul settled in Missouri as a farmer.
Carl Vogt began studying medicine at the University of Giessen in 1833, but soon switched to chemistry under the influence of Justus Liebig, a pioneer of organic chemistry. Liebig’s experimental approach, which rejected the traditional divide between living and non-living matter, helped lay the groundwork for Vogt’s later materialist views. In 1835, however, Vogt had to leave Giessen after helping a politically persecuted student escape. He fled to Switzerland and completed his medical degree in 1839.
In the early 1840s, Vogt became active in both scientific and political reform circles, though he had not yet fully adopted a materialist worldview. His ideological shift took place during a three-year stay in Paris, where he came into contact with anarchist thinkers like Mikhail Bakunin and Pierre-Joseph Proudhon. These interactions significantly influenced his political ideas. Starting in 1845, Vogt published the Physiological Letters, which aimed to make physiology more accessible to the public. Inspired by Liebig’s Chemical Letters, the early volumes were written in clear, popular language. While the first letters avoided strong ideological claims, the 1846 letter on the nervous system marked a turning point. In it, Vogt argued that consciousness, will, and thought originate solely in the brain, a direct challenge to spiritual or dualist explanations of the mind.
At this stage, however, Vogt prioritized political activism over theory. In 1847, he was appointed professor of zoology in Giessen with the help of Liebig and Alexander von Humboldt. But shortly afterward, the Revolutions of 1848 broke out across Europe. When the uprising reached Giessen, Vogt led the local militia and was elected to represent Hesse-Darmstadt in the Frankfurt Parliament, a democratic assembly aiming to unify Germany. After the Prussian King Frederick William IV refused the crown offered by the parliament and conservative forces regained control, Vogt joined the remaining 158 deputies in Stuttgart to form the so-called rump parliament. This assembly was short-lived, and on 18 June 1849, troops from Württemberg forcibly shut it down. Vogt fled once again to Switzerland and took refuge at his family home.
With his political career in ruins and his academic post lost, Vogt returned to scientific work. His research from this point onward took on a more openly ideological tone, as he began to interpret biological processes through the lens of materialist philosophy.
Progression of the debate
Materialism controversy until 1854
In 1850, Vogt travelled to Nice to continue his zoological research, as his academic prospects in Germany remained uncertain. A year later, he published a book on animal societies, which combined zoological observations with a sharp political critique of the German state. In the book, Vogt argued in favor of anarchism, claiming that all forms of government and law were signs that humanity had not yet returned to its natural state. Vogt’s argument for anarchism was rooted in his biological and materialist worldview. He believed that humans, like animals, are entirely material beings and part of the natural world. Therefore, biology not only supported materialism but also challenged existing social and political structures.Despite—or because of—its controversial content, the book attracted public attention in Germany. In 1852, Vogt published Bilder aus dem Thierleben, which further developed his materialist views and strongly criticized German academic circles. He argued that any biologist who thinks clearly must recognize the truth of materialism, especially given the evidence from animal experiments. From this, he concluded that if mental functions depend on brain functions, then the soul cannot exist independently of the body or survive after death. Furthermore, if the brain operates according to natural laws, then so must the soul—leaving no room for free will:
Vogt argued that those who rejected these conclusions misunderstood the implications of physiological science. His criticism was partly aimed at Rudolf Wagner, an anatomist and physiologist from Göttingen, who had attacked Vogt in an 1851 article in the Augsburger Allgemeine Zeitung. Wagner accused Vogt of replacing God with “blind, unconscious necessity". Wagner also proposed that a child’s soul was composed of equal parts from the mother’s and father’s souls. Vogt responded sarcastically, pointing out that such an idea contradicted the theological principle of the soul’s indivisibility and was scientifically implausible. Instead, he argued, character traits—like physical features—are inherited from parents through the brain, and therefore the idea of a "composite soul" could be explained in purely materialist terms.