Sentience
Without a head, a brain, a mind, in fact, no organs of any kind, the question of plant sentience would seem to be an open-and-shut case. But recently, books like Michael Marder’s Plant-Thinking, Michael Pollan’s The Intelligent Plant, and a few others have reignited the desire to prove plant sentience scientifically. Raja and Segundo-Ortín outline the field of plant studies and its search for sentience, dating its origins to Darwin’s On the Movement of Plants in the 1880s, but then leap to the current scientific literature of the last decade (2010–2020).[1]The question of plant sentience of course dates back much further than Darwin, to ancient Greek and Roman authors (Stoics, Aristotle, and Galen). It also overlaps with the ancient belief systems such as animism in Manichaeism, Tibetan Buddhism, and Indian Jainism, as well as more contemporary forms in Latin America, and Indigenous societies worldwide. Many of these traditions share stories in which trees talk and plants bleed. Endowed with spirit, perspective, or personhood, ancient traditions assumed vegetal awareness of some sort. To enter the debate about plant sentience is to step into muddy waters, for there is no clear separation between the ancient and more “scientific” understandings of sentience. Nowadays, discussions of plant sentience still reference ancient and Indigenous notions but also refer to contemporary fields and concepts such as artificial intelligence, the neural underpinnings of cognitive function, and neuroplasticity, as well as subjectivity, affect, and consciousness.
The search for plant sentience is fraught with complex differentiations, conflated categories, and ambiguous terminology, and there is no consensus on definitions. The most widely shared definition of sentience refers to “the capacity to feel.”[2] But what counts as feeling? Can sensing and reacting to the environment count as feeling, or do plants also need to feel pain to be sentient? And what evidence would be sufficient to demonstrate that a plant feels—without making assumptions about “interior experience” or only based on inference?[3]Another way of putting the question is: Does sentience rely on a subjective awareness of the environment or merely the capacity to process information and adaptive behavior?[4] Critics of the approaches that centralize “plant feelings” claim there is a widespread conflation of notions of pain, which is a subjective feeling, and nociception, which is a physical defense response.[5]
Many proponents of plants’ capacity to feel rely on a series of analogies, extending sentience from human to animal feeling in order to infer the existence of plant feeling. In an attempt to clarify what the “capacity to feel” might look like for plants, Stevan Harnad distinguishes between cognitive states and cognitive capacities. He says that while cognitive capacities can be observed and measured, feelings are cognitive states that cannot be measured, only correlated. Questions concerning animal sentience have traditionally relied on such correlations for evidence. Similarly, any claims to plant sentience would have to be based on correlation, and yet the criteria that could support such correlations have yet to be agreed upon.
The vast range of terminological difficulties presents challenges to the search for plant sentience. Terms such as “feelings,” “behavior,” “cognition,” and “sentience” were originally established in experimental psychology without reference to scientific criteria.[6]For example, “to feel” occupies an ambiguous space between emotion and sensation. Psychology defines sensation as the processing of stimulation by sensory organs. Affect, on the other hand, can refer to moods, motives, or intentions. (A feeling might be both sensation and feeling, Booth shows, but he warns that they should not be conflated, using the example “the boiling water in the pot is not feeling hot, reacting angrily, or taking action for the cook; there is just agitation of atoms.”) In certain contexts, Booth continues, behavior and cognition can mean the same thing: Information content is transformed from a selection of inputs into a choice for output. Behavior is not movement, nor what is observed without reference to input. Booth takes great pains to resolve the ambiguities between feeling and sense in order to apply these psychological terms to plants. Describing how the bean plant wraps itself around and climbs a pole, Booth demonstrates how the plant makes “decisions.” However, his description in the language of psychology alone proves insufficient; his rhetoric notably shifts from the language borrowed from psychology to metaphors of information processing (input/output, process, system, etc.). I point this out not to challenge the sentience of the bean plant per se but rather to insist that a pure “scientific” description of sentience is not possible. That is, the struggle to clarify the meaning of terms or conceptualize an extension of sentience across species involves not only empirical evidence but also borrowing established disciplinary language and correlating by means of analogy.
Plant sentience is often justified by means of an analogy between the animal nervous system and the network of transmission in plants. Some go so far as to claim that “plants do have a nervous system,”[7]and this “electrical communication system” is not just metaphorically similar but “is” the same as the animal nervous system. Andrea Nani and colleagues suggest that consciousness requires sentience, but sentience doesn’t imply consciousness. They propose a continuum of behaviors, moving from simple to complex, to reveal degrees of that plant sentience. Degrees are measured through adaptiveness, sensitivity, and sentience (defined as “restricted to the immediate perception of something happening to themselves”).[8]Nani argues that plants can have high levels of sentience but don’t carry other complex structures necessary to classify as consciousness. Still, this language remains problematic since it engages with the same predicates as Booth’s plant “decisions.” Moreover, the comparison between plants and animals involves an analogic structure, which can be misleading. Using parallel situations, the shared properties are inferred but are difficult to prove. Correlation arguments may be rhetorically persuasive, but mere inference does not provide evidence of sentience as part of that correlation.
Ginsburg and Jablonka argue that Nani’s correlation continuum of sentience—or any attribution of sentience to plants—is fundamentally based on the axiom that consciousness is an inherent aspect of life.[9]Ginsburg and Jablonka implicitly invoke panpsychism here, which has ancient roots. The first Greek philosopher, Thales, claimed that “everything is full of gods,” while the Stoics proposed to call this life force pneuma. Fast-forward several centuries, and Spinoza’s monads and James’s “psychical realities” made way for contemporary forms in David Chalmers and Thomas Nagel’s quality of mind. Steven Shaviro refers to panpsychism as both an “extravagant” and largely unverifiable thesis that is nevertheless a “recurring underground motif in the history of Western thought.”[10]Panpsychism is the view that “all things have mind or a mind-like quality”[11]or that “the basic physical constituents of the universe have mental properties.”[12]The long history of panpsychism is alluring to some proponents of plant sentience. According to the biopsychic view, sentience is universal, “an inherent feature of living organic forms.”[13]
The notion that all cognition emerged from primitive varieties fuels the Cellular Basis of Consciousness (CBC) model in evolutionary biology. Baluška and Reber argue that prokaryotic cells “have a natural unity, valence-marked ‘mental’ representations” and thus justify using the terms “consciousness,” “sentience,” “mind,” and “awareness” synonymously.[14]CBC is based on three core principles: (1) life and sentience are coterminous, which means that consciousness is an inherent feature of all life; (2) once a form or function plays an adaptive role in the life of a species, it remains as part of the genome (forever); and (3) cellular consciousness is generated by normal cell functions. The core claim of CBC is that all living organisms (including plants) will eventually be proven sentient. However, Ginsburg and Jablonka are skeptical of both philosophy’s panpsychism and biology’s CBC and ask: If all life is conscious in some way, how can we understand the relationship between the consciousness of a dog and the consciousness of the elementary particles that make up the dog? In other words, how do the macro and micro levels of cognition cohere with levels of consciousness? Maher argues that the predicate “is conscious” is simply indeterminate when applied to plants.[15]The relation of micro to macro and indeterminacy mirrors fundamental questions in quantum physics. Echoing Richard Feynman, plant studies characterize relations between the micro and the macro scale as “mysterious and incomprehensible.”[16]
It’s no wonder, then, that some plant scholars, such as Chauncey Maher, claim that the question of whether plants are sentient simply cannot be answered. Jonathan Birch, Segundo-Ortín, and Calvo agree that there is not much empirical evidence for sentience. Despite the lack of evidence, plant sentience appeals to many. Watching the bean shoot develop in time-lapse film is an amazing spectacle, says Birch, which makes one hopeful and provokes the (human) feeling that plants are making “decisions.”[17]Empirical methods are inadequate to proving plant consciousness, claims Maher; the evidence for plant sentience or some type of consciousness is founded on “extraordinary speculation” and “conceptual engineering,” instead.[18] It is precisely this conceptual engineering that one of the most insistent voices in plant sentience argues that we need. Paco Calvo allows that 95 percent of plant biologists reject plant sentience. Nevertheless, he challenges us to imagine new ways of living with plants, spawning new approaches to the ecological crisis.[19]And it’s just such feats of conceptual engineering, according to Calvo, that we require in the face of rampant ecosystem devastation.
While the debate over whether plants are sentient rages on, and empirical evidence for the sentience continues to fall short, it seems to me that the more interesting question here concerns the human inclination to prove or disprove plant sentience. What criteria count, what methods are sufficient, and how are boundaries drawn? As Douglas Hofstadter argues, whether we attribute consciousness to a particular entity or not, we all must draw the line somewhere.[20] It’s the human activities involved in this act of drawing that line that fascinate me.
Conceptual engineering that invents a kind of plant sentience may (or may not) generate new approaches to the ecological crisis, but they don’t by themselves prove anything about plant sentience. My point is simply that human engineering produces metaphors, analogies, terminology, correlations, persuasive arguments, and concepts that will structure how we think about and experience the plant behavior. Manipulating metaphors might make the idea of plant sentience more or less palatable, depending on the audience or agenda. Leah Ceccarelli convincingly argues that Schrödinger’s shrewd use of metaphors that appealed to both physicists and biologists effectively inspired their marriage in the invention of molecular biology. The quest to prove plant sentience today is marked by a split between two basic aims. The first seeks evidence of plant intelligence in order that it might serve as a model for artificial intelligence (in bioengineering, biorobotics, etc.). The second seeks evidence for plants as cognitive beings deserving of plant rights and social justice.[21] It should not come as a surprise, then, that scholars concerned with intelligence tend toward computational language of signaling, information, and code, while humanities plant scholars concerned with cognition and feeling enlist older, animist metaphors and combine them with contemporary language from the fields of biology, psychology, and neuroscience.
This brings us to the question of why plant studies as a “field” are interested in sentience, and why now, and in this way? Why are vastly different disciplines, ranging from biology, philosophy, cognitive science, and psychology to neurobiology, social science, information science, and Indigenous studies overlapping around the question of sentience in plants? Many people point to our planetary ecological crisis and argue that the extractivist mindset could be mitigated through empathy toward plants and the environment. I’m not convinced that this sort of activism toward empathy of sentient “others” will ever achieve the desired peaceful results. Sria Chatterjee notes that historically, the search for plant sentience has been mobilized in violent ways, ranging from bioengineering and the manufacture of plant robots to anticolonial Hindu nationalism.[22] Most plant humanities scholars engage in the debate around sentience because they assume that it will lead to some form of increased social justice. However, Chatterjee argues that broadening the range of sentient beings does not necessarily lead to equity or new forms of ecological care. Instead, nonhuman agencies are easily adapted to “vegetal work,” in other words, new forms of production and labor that in fact sustain the human-centered extractive economy.[23]
To my mind, the question of plant sentience in itself is not the issue. Rather, if we prove to ourselves (that is, if we believe) that plants aresentient, then certain cultures, outcomes, relations, and therefore politics are the consequence of their sentience. If we prove to ourselves that plants are not sentient, then we arrive at different cultures, outcomes, and relations and therefore different politics. The Truth about plant sentience, as Nietzsche would say, “is incomprehensible and not worth knowing.”[24] In other words, the only way to secure Truth is to forget the techniques that produced it. So, it is not the particular form of plant sentience that matters for us—whether it be intelligence, sensing individuality, responsiveness, intentionality, communication networks, or agential force—but rather how we arrived at a particular form of sentience.
If humans desire to give plants a voice, then we’re clearly left with more questions than answers. In this spirt, we’d do well to ask: What is the context in which the question of plant sentience (re)emerges, what are the modes of inquiry that support it, and what can and cannot be said about sentience in a particular time and place? What, in other words, is the framework within which critical plant studies take shape and through which their categories, boundaries, and criteria of proof are (re)enforced and maintained? What are the principles of exclusion, the rules of classification and legitimacy, the practices and procedures that control and limit what we can and cannot say about plant sentience? And finally, a question of desire: What do we want in wanting to know whether plants are sentient?
Notes
[1] Vicente Raja and Miguel Segundo-Ortin, “Plant Sentience: Theoretical and Empirical Issues: Editorial Introduction,” Journal of Consciousness Studies 28, no. 1–2 (2021): 7–16.
[2] Donald M. Broom, “Concepts and Interrelationships of Awareness, Consciousness, Sentience, and Welfare,” Journal of Consciousness Studies 29, no. 3–4 (2022): 129–49.
[3] Carel ten Cate, “Plant Sentience: A Hypothesis Based on Shaky Premises,” Animal Sentience 8, no. 33 (2023): 13.
[4] Lincoln Taiz et al., “Plants Neither Possess nor Require Consciousness,” Trends in Plant Science 24, no. 8 (2019): 677–87.
[5] Deborah Brown and Brian Key, “Plant Sentience, Semantics, and the Emergentist Dilemma,” Journal of Consciousness Studies 28, no. 1–2 (2021): 155–83.
[6] David A. Booth, “Sentience: Back to the Science from the Words,” Animal Sentience 8, no. 33 (2023).
[7] Paco Calvo, Vaidurya Pratap Sahi, and Anthony Trewavas, “Are Plants Sentient?” Plant, Cell & Environment 40, no. 11 (2017): 2858–69.
[8] A. Nani, G. Volpara, and A. Faggio, “Sentience With or Without Consciousness,” Journal of Consciousness Studies 28, no. 1–2 (2021): 60–79.
[9] Simona Ginsburg and Eva Jablonka, “Sentience in Plants: A Green Red Herring?” Journal of Consciousness Studies 28, no. 1–2 (2021): 17–33.
[10] Steven Shaviro, “Consequences of Panpsychism,” in The Nonhuman Turn, ed. Richard Grusin (University of Minnesota Press, 2015).
[11] David Skrbina, “Panpsychism in History: An Overview,” in Mind That Abides, ed. David Skrbina (Benjamins, 2009).
[12] Nagel, Thomas. “What Is It Like to Be a Bat?” in The Language and Thought Series (Harvard University Press, 1980), 159–68.
[13] Arthur S. Reber, The First Minds: Caterpillars, ‘Karyotes, and Consciousness (Oxford University Press, 2018).
[14] František Baluška and Arthur S. Reber, “The Biomolecular Basis for Plant and Animal Sentience: Senomic and Ephaptic Principles of Cellular Consciousness,” Journal of Consciousness Studies 28, no. 1–2 (2021): 31–49.
[15] Chauncey Maher, “The Indeterminacy of Plant Consciousness,” Journal of Consciousness Studies 28, no. 1–2 (2021): 136–54.
[16] Ginsburg and Jablonska, “Sentience in Plants.”
[17] Jonathan Birch, “The Search for Invertebrate Consciousness,” Noûs 56, no. 1 (2022): 133–53.
[18] Maher, “The Indeterminacy of Plant Consciousness.”
[19] Calvo, Sahi, and Trewavas, “Are Plants Sentient?”
[20] Douglas R. Hofstadter, I Am a Strange Loop (Basic Books, 2007), 18.
[21] Raja and Segundo-Ortín, “Plant Sentience.”
[22] Sria Chatterjee, “Political Plants: Art, Design, and Plant Sentience,” Cultural Politics 19, no. 1 (2023): 88.
[23] Sria Chatterjee, “Political Plants,” 95.
[24] Friedrich Nietzsche, “On Truth and Lying in an Extra-Moral Sense,” in Friedrich Nietzsche on Rhetoric and Language, ed. Sander L. Gilman, Carole Blair, David J. Parent and trans. David J. Parent (Oxford University Press, 1989).