Gustav Theodor Fechner championed the idea that plants have souls – something we might call ‘consciousness’ today. I first learned of him in an interdisciplinary reading group on plant consciousness that I co-lead at Harvard University. We convene biologists, theologians, artists and ethologists to explore the burgeoning literature on plant life. We found Fechner covered in the New York Times bestselling book by Christopher Bird and Peter Tompkins titled The Secret Life of Plants (1973). Michael Pollan describes this book as a ‘beguiling mashup of legitimate plant science, quack experiments, and mystical nature worship that captured the public imagination at a time when New Age thinking was seeping into the mainstream.’ The Secret Life of Plants cites Fechner as an important but often forgotten champion for plant sentience.

In 2006, 30 years after The Secret Life of Plants, a bold group of scientists published an article calling to establish the field of ‘plant neurobiology’ with the goal of ‘understanding how plants perceive their circumstances and respond to environmental input in an integrated fashion’. In other words, how plants might have something like minds.

The burgeoning field of plant science has become a rich playground for profound questions that have beguiled Western philosophy since Plato: namely, what is mind, where does it extend, and how? Who has mind, and how do we know? While scientists increasingly agree that many animals are sentient, doubts remain about our vegetal kin. For many, plants remain a limit case in the types of beings we are willing to concede experience life with the richness humans do, or whose experience we can meaningfully study.

Fechner, writing more than 150 years ago, anticipated many claims of the contemporary plant neurobiology movement. His thought stands like an oasis amid an intellectual history otherwise hostile to plants. After all, in De Anima, Aristotle deemed plants the lowest form of life, construing them as defective animals. Francis Bacon later construed science as a method of torturing nature. And René Descartes not only reduced animals to unthinking automata, but fundamentally ruptured the relationship between matter and mind.

Fechner would spend his whole life trying to heal the divide between mind and matter, and the commensurate split between philosophy and science – but, first, he had to go mad.

Fechner was born on 19 April 1801 in Groß Särchen, Saxony, the second child of Samuel Traugott Fischer and Dorothea Fechner. Fechner’s father Samuel was a pastor, and also the first person in the village to vaccinate his children. He installed a lightning rod on the church roof, and spoke Latin to his young son. He died when Gustav was only five.

At 16, Fechner matriculated into the University of Leipzig as a medical student. ‘After my medical studies,’ Fechner lamented, ‘I became a complete atheist … I saw only a mechanical gear in the world.’ Capitulating to this mechanical worldview, he abandoned medicine to study physics.

In February 1820, Fechner stumbled upon a copy of Grundriß der Naturphilosophie (1802) by Lorenz Oken, and ‘a new light suddenly seemed to illuminate the whole world to me. I was blinded by it.’ The project of Naturphilosophie promised a great unified worldview, one that struck Fechner with urgent necessity. Fechner could not, however, disavow his love of measurements, experiments and equations. Compared with physics, the sprawling top-down speculations of German idealism seemed insufficient. Rigorous systematicity was the ‘only way to achieve clear, reliable, and fruitful results’. Fechner still longed to apprehend the invisible laws that caused creation to ring in his ears like a symphony.

Showing how brain stimulation affected bodily movement threatened to make notions of the ‘soul’ indefensible

When Fechner was born, Germany was still a philosophical powerhouse. Immanuel Kant, Johann Gottlieb Fichte, Friedrich Schelling and Johann Wolfgang von Goethe made the first three decades of the 19th century some of the most philosophically creative in modern history. After G W F Hegel died in 1831, major discoveries in biology, physiology and psychology laid the groundwork for an understanding of life in mathematical terms. As the empirical sciences grew in prestige and authority, Ludwig Feuerbach, Carl Vogt, Ludwig Büchner and other thinkers argued that every living leaf, flower and fox could be explained by appeals to the physical and chemical properties of matter.

To some, 19th-century advances in psychology seemed to make philosophy obsolete. The new field of psychology claimed to treat the mind – that old domain of philosophy – according to observational and increasingly quantitative methods. Anatomical experiments showing how brain stimulation affected bodily movement threatened to make philosophical notions of the ‘soul’ indefensible.

Fechner embraced the standards of material, empirical observation even as he harboured a secret love of the dying Naturphilosophie. He studied physics with greater intensity, and he accepted a physics professorship in 1834 at the University of Leipzig, and lectured without pay. To pay his bills, he translated multi-volume physics and chemistry works from French into German. Desperate for work, the Latin-speaking doctor-turned-physicist found himself translating the eight-volume Hauslexikon, a 19th-century equivalent of the Ladies’ Home Journal, many thousands of pages long. The tedium – the inanity – of Hauslexikon broke his spirit. Fechner worked himself into exhaustion. He was also going........

© Aeon