The ethics of uncertain sentience is an area of applied ethics concerned with decision-making when it is unclear whether a being is sentient, understood as capable of subjective experience, feeling, or perception. The issue arises prominently in animal ethics, especially for invertebrates such as crustaceans and insects and for fish, where the possibility of pain is contested; it also features in debates in environmental ethics, the ethics of artificial intelligence and neuroethics.
Proposed responses in the literature include decision rules, with the precautionary principle most commonly invoked, alongside incautionary and expected-value approaches (including probabilistic variants); virtue-ethical arguments for attentiveness and caution toward possibly sentient animals; and assessment frameworks in animal welfare science. Ongoing discussion considers evidential standards, potential regulatory and economic costs, and the scope of moral consideration across diverse biological taxa and computational substrates.
Animal ethics
Invertebrates
Crustaceans and cephalopods
David Foster Wallace's 2004 essay "Consider the Lobster" describes the Maine Lobster Festival and poses the problem of inferring pain across species. It notes evidence of nociceptors in lobsters alongside uncertainty about endogenous opioids, and reflects on the ethics of killing and cooking animals alive; building on this, Robert C. Jones's chapter "The Lobster Considered" engages Wallace's essay and argues that current evidence supports treating lobsters as capable of pain and thus as morally considerable. Jones reviews neurophysiological and behavioural work on nociception and opioid systems, distinguishes moral considerability from degrees of moral significance, and concludes that, given residual uncertainty, a precautionary approach is warranted toward practices that risk causing pain to crustaceans.
A 2021 UK government-commissioned review by the London School of Economics evaluated 300 studies and concluded that cephalopods and decapod crustaceans should be treated as sentient, grading the evidence as "very strong" for octopods, "strong" for most crabs, and "substantial but not strong" for squid, cuttlefish, and lobsters; it recommended best-practice transport, stunning, and slaughter and said lobsters and crabs should not be boiled alive, informing debate on the Animal Welfare (Sentience) Act.
Insects
In 2016, Shelley A. Adamo reviewed philosophical, neurobiological, behavioural, robotic, and evolutionary lines of evidence on insect pain and concluded that the question remains unsettled: insects clearly show nociception and complex learning, but similar pain-like behaviours can arise from simpler mechanisms and can be engineered in robots, so argument-by-analogy to human pain is weak without a clear account of the neural architecture needed for subjective experience. She contrasts Morgan's canon with the precautionary principle, noting that they point to opposing policy responses and that precaution has research and economic costs; she nonetheless urges careful handling to avoid stress for methodological and ethical reasons.
In an article for Vox, Dylan Matthews examines the question of insect sentience in proposals to scale entomophagy, reporting limited evidence on whether farmed insects feel pain and on the welfare impact of common slaughter methods (e.g. freezing and shredding). He cites estimates that around 1 trillion insects are raised and killed annually, with about 79–94 billion alive at any time, and argues that if insects can suffer the ethical implications of expanding insect farming would be substantial.
Fish
Maximilian Padden Elder argues that contemporary evidence warrants treating fish as potential sufferers within animal ethics. He distinguishes nociception from conscious pain and contends that teleosts possess nociceptors and display behaviours consistent with affective states. Objections that fish cannot suffer because they lack a neocortex, or because they do not exhibit human-like pain displays, are described as anthropocentric; Elder notes subcortical processing and behavioural data that weaken neocortex-based dismissals and cautions against using human responses as the standard for other species. He also discusses cultural and psychological factors that reduce empathy for fish and thereby lower concern for their welfare.
Given remaining uncertainty, Elder advocates a precautionary approach that shifts the burden of proof to those whose actions risk harm. He cites policy analogues (the U.S. Marine Mammal Protection Act, UK protection of cephalopods, and EU uses of the precautionary principle) and points to scale as a reason for priority, noting estimates of roughly 1–2.7 trillion wild-caught fish annually and tens of billions of farmed fish slaughtered in a single year. He draws out implications for commercial and recreational fishing and questions the coherence of moral pescetarianism in light of possible fish suffering.
Decision principles and frameworks
In the 2015 essay "Reconsider the Lobster", Jeff Sebo quotes Wallace's discussion of the difficulty of establishing whether an animal can experience pain. Sebo calls the question of how to treat individuals of uncertain sentience, the "sentience problem" and argues that this problem which "Wallace raises deserves much more philosophical attention than it currently receives." Sebo asserts that there are two motivating assumptions behind the problem: "sentientism about moral status"—the idea that if an individual is sentient, then they deserve moral consideration—and "uncertainty about other minds", which refers to scientific and philosophical uncertainty about which individuals are sentient.
In response to the problem, Sebo lays out three different potential approaches: the incautionary principle, which postulates that in cases of uncertainty about sentience it is morally permissible to treat individuals as if they are not sentient; the precautionary principle, which suggests that in such cases we have a moral obligation to treat them as if they are sentient; and the expected value principle, which asserts that we are "morally required to multiply our credence that they are by the amount of moral value they would have if they were, and to treat the product of this equation as the amount of moral value that they actually have". Sebo advocates for the latter position.
Jonathan Birch proposes a practical framework grounded in the precautionary principle for assessing animal sentience and argues that it is consistent with established practice in animal welfare science.
Simon Knutsson and Christian Munthe argue that from the perspective of virtue ethics, that when it comes to animals of uncertain sentience, such as "fish, invertebrates such as crustaceans, snails and insects", that it is a "requirement of a morally decent (or virtuous) person that she at least pays attention to and is cautious regarding the possibly morally relevant aspects of such animals".
Environmental ethics
Kai Chan advocates for an environmental ethic, which is a form of ethical extensionism applied to all living beings because "there is a non-zero probability of sentience and consciousness" and that "we cannot justify excluding beings from consideration on the basis of uncertainty of their sentience".
Ethics of artificial intelligence
Nick Bostrom and Eliezer Yudkowsky argue that if an artificial intelligence is sentient, then it is wrong to inflict it unnecessary pain, in the same way that it is wrong to inflict pain on an animal, unless there are "sufficiently strong morally overriding reasons to do so". They also advocate for the "Principle of Substrate Non-Discrimination", which asserts: "If two beings have the same functionality and the same conscious experience, and differ only in the substrate of their implementation, then they have the same moral status."
Soenke Ziesche and Roman Yampolskiy coined the term "AI welfare" and outlined the new field of AI welfare science, which is derived from animal welfare science.
Neuroethics
Adam J. Shriver argues for "precise, precautionary, and probabilistic approaches to sentience" and asserts that the evidence provided by neuroscience has differing relevance to each; he concludes that basic protections for animals should be guided by the precautionary principle and that although neuroscientific evidence in certain instances is not necessary to indicate that individuals of certain species require protections, "ongoing search for the neural correlates of sentience must be pursued in order to avoid harms that occur from mistaken accounts."
