Kevin Tobia

Scholarship in experimental jurisprudence has reported surprising findings about various concepts of legal significance: _acting intentionally_, _causation_, _consent_, _knowledge, recklessness_, _reasonableness,_ and _law_ itself. Often, these studies examine laypeople’s ordinary concepts and draw broader conclusions about legal experts’ concepts. This Article questions such inferences, from empirical findings about ordinary concepts to conclusions about the concepts of those with legal expertise. It presents a case study concerning what it means to act _intentionally._ An experiment examines intentionality judgments across four populations (N = 774): laypeople, law students, non-law students, and United States judges. Legal training affected judgments in three ways that are consistent with the acquisition of a distinctive legal concept. This case study supports the Article’s broader claim: Laypeople’s ordinary concepts are not equivalent to experts’ legal concepts. The acquisition of legal concepts is an important form of legal expertise.

A cross-cultural survey experiment revealed a dominant tendency to rely on a rule’s letter over its spirit when deciding which behaviors violate the rule. This tendency varied markedly across (k = 15) countries, owing to variation in the impact of moral appraisals on judgments of rule violation. Compared with laypeople, legal experts were more inclined to disregard their moral evaluations of the acts altogether and consequently exhibited stronger textualist tendencies. Finally, we evaluated a plausible mechanism for the emergence of textualism: in a two-player coordination game, incentives to coordinate in the absence of communication reinforced participants’ adherence to rules’ literal meaning. Together, these studies (total n = 5,794) help clarify the origins and allure of textualism, especially in the law. Within heterogeneous communities in which members diverge in their moral appraisals involving a rule’s purpose, the rule’s literal meaning provides a clear focal point—an identifiable point of agreement enabling coordinated interpretation among citizens, lawmakers, and judges.

Jurisprudence aims to identify and explain important features of law. To accomplish this task, what procedure or method should one employ? Elucidating Law, a tour de force in “the philosophy of legal philosophy,” develops an instructive account of how philosophers “elucidate law,” which elucidates jurisprudence’s own aims and methods. This Review introduces the book, with emphasis on its discussion of methodology. Next, the Review proposes complementing methodological clarification with methodological innovation. Jurisprudence should ask timeless questions, but its methods need not stagnate. Consider that jurisprudence has a long tradition of asserting claims about how “we” understand the law---where “we” might refer to all people, ordinary people, legal experts, or legal officials. There are now rich empirical literatures that bear on these claims, and methods from “experimental jurisprudence” and related disciplines can assess untested assertions. Today’s jurisprudence can achieve greater rigor by complementing traditional methods with empirical ones.

Do you persist as the same person over time because you keep the same mind or because you keep the same body? Philosophers have long investigated this question of personal identity with thought experiments. Cognitive scientists have joined this tradition by assessing lay intuitions about those cases. Much of this work has focused on judgments of identity continuity. But identity also has practical significance: obligations are tagged to one's identity over time. Understanding how someone persists as the same person over time could provide insight into how and why moral and legal obligations persist. In this paper, we investigate judgments of obligations in hypothetical cases where a person's mind and body diverge (e.g., brain transplant cases). We find a striking pattern of results: In assigning obligations in these identity test cases, people are divided among three groups: “body‐followers,” “mind‐followers,” and “splitters”—people who say that the obligation is split between the mind and the body. Across studies, responses are predicted by a variety of factors, including mind/body dualism, essentialism, education, and professional training. When we give this task to professional lawyers, accountants, and bankers, we find they are more inclined to rely on bodily continuity in tracking obligations. These findings reveal not only the heterogeneity of intuitions about identity but how these intuitions relate to the legal standing of an individual's obligations.

Many experimental philosophers are philosophers by training and professional affiliation, but some best work in experimental philosophy has been done by people who do not have advanced degrees in philosophy and do not teach in philosophy departments. This chapter explains that the experimental philosophy is the empirical investigation of philosophical intuitions, the factors that affect them, and the psychological and neurological mechanisms that underlie them. It explores what are philosophical intuitions, and why do experimental philosophers want to study them using the methods of empirical science. The positive program in experimental philosophy shares the goal of the substantial part of traditional philosophy that is concerned with the analysis of important philosophical concepts. The negative program has implications for philosophical projects whose goal is conceptual analysis. There have been a number of responses to the challenge posed by experimental philosophy's negative program. The chapter also focuses on the expertise defense.

Abstract:Appeal to intuition has played an important role in philosophical debates. Recent research in experimental philosophy empirically investigates philosophical intuitions, the factors that affect them, and the psychological and neurological mechanisms that underlie them. We distinguish between two common ways in which intuitions are used as philosophical evidence and present experimental philosophical studies that problematize these uses of philosophical intuitions. These studies indicate the influence of various prima facie irrelevant factors, such as language and order of presentation, on philosophical intuitions. We consider three versions of the “expertise defense” of philosophical intuition and identify deficiencies in those defenses. We do not conclude that intuitions should never be used as philosophical evidence. Instead, we contend that experimental philosophy, broadly construed, has a crucial role to play in assessing and improving philosophical methodology Resumo: O apelo à intuição desempenhou até o presente um papel importante em debates filosóficos. Pesquisas recentes em filosofia experimental examinam as intuições filosóficas empiricamente, os fatores que as afetam e os mecanismos psicológicos e neurológicos que as subjazem. Distinguimos entre dois modos comuns nos quais as intuições são usadas como evidência filosófica e apresentamos estudos experimentais filosóficos que problematizam esses usos das intuições filosóficas. Esses estudos indicam a iFilosofia nfluência de diversos fatores prima facie irrelevantes, como a linguagem e a ordem de apresentação. Consideramos três versões da “defesa do especialista” da intuição filosófica e identificamos deficiências nessas defesas. Não concluímos que as intuições nunca devam ser usadas como evidência filosófica. Em vez disso, argumentamos que a filosofia experimental, amplamente concebida, tem um papel crucial a desempenhar na avaliação e na melhoria da metodologia filosófica.

How should judges decide which linguistic canons to apply in interpreting statutes? One important answer looks to the inside of the legislative process: Follow the rules that lawmakers contemplate. A different answer, based on the “ordinary meaning” doctrine, looks to the outside: Follow the rules that would guide an ordinary person’s understanding of the legal text. Empirical scholars have studied statutory interpretation from the inside—revealing what rules drafters follow—but never from the outside. We offer a novel framework for empirically testing interpretive canons “from the outside,” recruiting 4,500 people from the United States, as well as a sample of U.S. law students, to evaluate hypothetical scenarios that correspond to each canon’s triggering conditions. The empirical findings provide crucial evidence about which traditional canons “ordinary meaning” actually supports, and they carry several further implications. First, interpretive canons are not a closed set. We discovered new canons that are not yet reflected as legal canons, including one we term the “non-binary gender canon” and another the “quantifier domain restriction canon.” Second, the results support a new understanding of the ordinary meaning doctrine itself, as one focused on the ordinary interpretation of rules, as opposed to the traditional focus on “ordinary language” generally. Third, many of the canons reflect that ordinary people interpret rules with an intuitive anti-literalism. This anti-literalism finding challenges textualist assumptions about ordinary meaning, as well as offering a theme for researching other currently unrecognized canons. Most broadly, we hope the Essay initiates a new research program in empirical legal interpretation. If ordinary meaning is relevant to legal interpretation, interpreters should look to evidence of how ordinary people actually understand legal rules. We see our experiments as a first step in that new direction.

A cross-cultural survey experiment revealed a widespread tendency to rely on a rule’s letter over its spirit when deciding which acts violate the rule. This tendency’s strength varied markedly across (k = 15) field sites, owing to cultural variation in the impact of moral appraisals on judgments of rule violation. Compared to laypeople, legal experts were more inclined to disregard their moral evaluations of the acts altogether, and consequently exhibited more pronounced textualist tendencies. Finally, we evaluated a plausible mechanism for the emergence of textualism: In a two-player coordination game, incentives to coordinate in the absence of communication reinforced participants’ adherence to rules’ literal meaning. Together, these studies (Ntotal = 5495) help clarify the origins and allure of textualism, especially in the law. Within heterogeneous communities in which members diverge in their moral appraisals involving a rule’s purpose, the rule’s literal meaning provides a clear focal point—an easily identifiable point of agreement enabling coordinated interpretation among citizens, lawmakers and judges.

Legal theorists seek to persuade other jurists of certain theories: Textualism or purposivism; formalism or realism; natural law theory or positivism; prison reform or abolition; universal or particular human rights? Despite voluminous literature about these debates, tremendous uncertainty remains about which views experts endorse. This Article presents the first-ever empirical study of American law professors about legal theory questions. A novel dataset of over six hundred law professors reveals expert consensus and dissensus about dozens of longstanding legal theory debates. Law professors also debate questions about the nature of the legal academy. Descriptively, which subjects (e.g. constitutional law) and methods (e.g. law & economics) are most central within the legal academy today? And prescriptively, should today’s legal academy prioritize additional areas (e.g. legislation) or methods (e.g. critical race theory)? There is great interest in these questions but no empirical dataset of experts’ views; this results in uncertainty about which views experts endorse. This Article’s empirical study also clarifies these questions, documenting law professors’ evaluation of over one-hundred areas of law. The legal theory and legal academy findings support implications for legal scholarship, education, and practice. Clearly, debates about law and the legal academy’s evolution should not be settled by a survey. Nevertheless, insofar as law professors are experts about these issues, it is instructive to discover and carefully examine what views those experts hold, so as to help determine which views are most likely to be true and how the legal academy ought to develop.

A recent wave of empirical legal scholarship reports surprising findings about various concepts of legal significance, including the concept of acting intentionally, causation, consent, knowledge, recklessness, reasonableness, and law itself. These studies typically examine laypeople, but often draw broader conclusions about legal experts or law. Findings about laypeople’s (“ordinary”) concepts have been taken to reflect the concepts of trained legal theorists, reveal biases affecting judges’ decision-making, and clarify subtle doctrinal features. This Article questions the validity of such inferences, from empirical findings about ordinary concepts to conclusions about the concepts of those with legal expertise. It presents a case study concerning what it means to act intentionally. An experiment examines the judgments of four populations (N = 774): lay people, law students, non-law students, and United States judges. Legal training affected judgments in three ways, all of which suggest the acquisition of a distinctive legal concept. This case study supports the Article’s broader conclusion: empirical evidence about laypeople’s ordinary concepts does not necessarily carry straightforward legal implications. This defuses provocative empirical challenges regarding biased judging, raises new questions about the relationship between judges and juries, and provides a broader proof of principle: The acquisition of legal concepts is an under-studied but central form of legal expertise.

Perhaps the most fundamental principle of legal interpretation is the presumption that terms should be given their “ordinary” (i.e., general, non-technical) meanings. This principle is a central tenet of modern textualism. Textualists believe a universal presumption of ordinary meaning follows from their theory’s core commitment: A law should be interpreted consistently with what its text communicates to the ordinary public. This Article begins from this textualist premise, empirically examining what legal texts communicate to the public. Five original empirical studies (N = 4,365) reveal a surprising finding: Ordinary people consider genre carefully and regularly take terms in law to communicate technical legal meanings, not ordinary ones. This discovery carries implications for legal interpretation’s theory and practice. Modern textualists—especially at the Supreme Court—justify their theory through “democratic,” fair notice, and rule-of-law appeals to ordinary people. But the empirical studies reveal that fidelity to ordinary people does not imply an unwavering commitment to ordinary meaning. Instead, it requires interpreters to also look to technical meanings. On a practical level, the results support a new presumption of legal meaning and ground a new challenge to textualism’s claim to promote fair notice. As a case study, we consider Bostock v. Clayton County, Georgia, which held that both sexual orientation and gender identity discrimination are prohibited forms of sex discrimination. The Article’s empirics and theory offer a new justification of the Court’s landmark decision.

Textualism is now the Court’s lingua franca. In response, some have proposed a “progressive textualism,” defined by the use of traditional textualist methods to reach politically progressive results. This Article explores a different kind of “progressive textualism.” Rather than starting with the desired policy outcome—politically progressive or conservative—we begin from one of modern textualism’s central values: A commitment to “democratic” interpretation. As Justice Barrett argues, this commitment views textualists as “agents of the people” who “approach language from the perspective of an ordinary English speaker.” Textualists thereby claim to promote democracy by interpreting law consistently with what it communicates to the ordinary public. However, recent empirical studies reveal discrepancies between textualist interpretive commitments and how ordinary people understand legal texts. These discrepancies undermine claims that textualists’ methodology is committed to democratic interpretation. A textualism centered on democratic interpretation would be methodologically more progressive if it centered facts rather than fictions about how ordinary people interpret language. It would recognize that people understand legal language in light of linguistic “(co)text” and “(con)text,” and sometimes nonliterally; they often understand ambiguous terms in law to have legal, not ordinary, meanings; and their understanding of law is informed by its apparent purpose and sometimes by interpretive rules that are conventionally justified on normative grounds. In contrast, current textualism is often methodologically regressive, crafting a fictional “ordinary person” more closely connected to ideological policy goals than facts about ordinary language comprehension.

An increasing number of automated and artificially intelligent (AI) systems make medical treatment recommendations, including “personalized” recommendations, which can deviate from standard care. Legal scholars argue that following such nonstandard treatment recommendations will increase liability in medical malpractice, undermining the use of potentially beneficial medical AI. However, such liability depends in part on lay judgments by jurors: When physicians use AI systems, in which circumstances would jurors hold physicians liable? To determine potential jurors’ judgments of liability, we conducted an online experimental study of a nationally representative sample of 2,000 U.S. adults. Each participant read one of four scenarios in which an AI system provides a treatment recommendation to a physician. The scenarios varied the AI recommendation (standard or nonstandard care) and the physician’s decision (to accept or reject that recommendation). Subsequently, the physician’s decision caused a harm. Participants then assessed the physician’s liability. Our results indicate that physicians who receive advice from an AI system to provide standard care can reduce the risk of liability by accepting, rather than rejecting, that advice, all else equal. However, when an AI system recommends nonstandard care, there is no similar shielding effect of rejecting that advice and so providing standard care. The tort law system is unlikely to undermine the use of AI precision medicine tools and may even encourage the use of these tools.

Recent psychology research has established that people do not employ a simple unidimensional scale for attributions of personhood, increasing from non-sentient rocks to mentally complex humans. Rather, there are two personhood dimensions: agency (e.g. planning, deciding, acting) and experience (e.g. feeling, desiring, experiencing). Here we show that this subtle distinction also occurs in the semantic space of natural language. We develop computational-linguistics tools for measuring variation in agency and experience in language and validate the measures against human judgments. To demonstrate the usefulness of the method, we map both dimensions of personhood in historical English-language corpora over the last 200 years. First, we show that while women are now perceived as having similar levels of agency as men, they are still perceived as more patient-like. Second, we show that domesticated animals have gradually gained higher attributions of experience, but not agency, over time.

The legal corpus linguistics movement is one of the most exciting recent developments in legal theory. Justice Thomas R. Lee and Stephen C. Mouritsen are its pioneers, and their new article thoughtfully responds to critics. Here, Part I applauds their response as a cautious account of how those methods might, in some circumstances, provide relevant evidence about ordinary meaning in legal interpretation. Some disagreements persist, but The Corpus and the Critics makes significant progress in academic debates about legal interpretation. Part II turns from theory to practice: Judges are increasingly discussing corpus linguistics and conducting sua sponte analyses in their opinions, and this Essay collects and analyzes these cases. Corpus linguistics is theorized as apolitical, neutral, and objective. But in practice, it has been used largely by Republican-appointed judges, often inconsistently with standards that Lee and Mouritsen recently endorse. This Essay identifies a set of best practices, endorsed both by Lee and Mouritsen’s new cautious account and by many critics of the movement. It elaborates those commitments and evaluates whether they are met by courts citing or conducting legal corpus linguistics. If courts continue to employ legal corpus linguistics methods, the practice should be guided by these shared standards.

Today’s textualist Supreme Court draws a bright line between essential “linguistic” interpretive canons and suspect “substantive” canons. This Article’s thesis is that the venerable linguistic/substantive dichotomy is false. We present the first empirical study of whether ordinary people (N = 1,520) understand rules in line with some of law’s substantive canons. The study supports that some substantive canons represent valid linguistic generalizations about how ordinary people understand rules’ meaning. For example, the presumption against retroactivity is usually justified by values like fairness, but it also best reflects ordinary readers’ default understanding of rules’ meanings. In an age of textualism, this argument has direct practical implications. Interpreters committed to the ordinary reader should reconsider whether rules that have been traditionally described as “substantive canons” might also be linguistic ones. The article’s analysis also puts pressure on textualists to better justify their recent embrace of purely substantive canons, like the new “major questions” canon. Most broadly, the Article makes progress on a longstanding philosophical debate about facts and values in interpretation. Beyond the exclusively linguistic canons and the exclusively substantive canons, there is an important but overlooked category: The linguistic and substantive canons.

Should machines be judges? Some say no, arguing that citizens would see robot-led legal proceedings as procedurally unfair because “having your day in court” is having another human adjudicate your claims. Prior research established that people obey the law in part because they see it as procedurally just. The introduction of artificially intelligent (AI) judges could therefore undermine sentiments of justice and legal compliance if citizens intuitively take machine-adjudicated proceedings to be less fair than the human-adjudicated status quo. Two original experiments show that ordinary people share this intuition. There is a perceived “human-AI fairness gap.” However, it is also possible to reduce — and perhaps even eliminate — the fairness gap through “algorithmic offsetting.” Affording a hearing before AI judges and enhancing the interpretability of AI-rendered decisions reduce the human-AI fairness gap. Moreover, the procedural justice advantage of a human over AI appears to be driven more by beliefs about the accuracy of the outcome and thoroughness of consideration, rather than doubts about whether a party felt it had a good opportunity to voice its opinions or whether the judge understood the perspective of the litigant. The results support a common and fundamental objection to robot judges: There is a concerning human-AI fairness gap. Yet, the results also indicate that the strongest version of this challenge — human judges have irreducible procedural fairness advantages — is not reflected in public views. In some circumstances, people see a day in robot court as no less fair than a day in human court.

Within legal scholarship and practice, among the most pervasive tasks is the interpretation of texts. And within legal interpretation, perhaps the most pervasive inquiry is the search for “ordinary meaning.” Jurists often treat ordinary meaning analysis as an empirical inquiry, aiming to discover a fact about how people understand language. When evaluating ordinary meaning, interpreters rely on dictionary definitions or patterns of common usage, increasingly via “legal corpus linguistics” approaches. However, the most central question about these popular methods remains open: Do they reliably reflect ordinary meaning? This Article presents a series of experiments that assess whether (a) dictionary definitions and (b) common usage data reflect (c) how people actually understand language today. The Article elaborates the implications of two main experimental results. First, neither the dictionary nor legal corpus linguistics methods reliably track ordinary people’s judgments about meaning. This shifts the argumentative burden to jurists who rely on these tools to identify “ordinary meaning” or “original public meaning”: these views must articulate and demonstrate a reliable method of analysis. Moreover, this divergence illuminates several interpretive fallacies. For example, advocates of legal corpus linguistics often contend that the nonappearance of a specific use in a corpus indicates that the use is not part of the relevant term’s ordinary meaning. The experiments reveal this claim to be a “Nonappearance Fallacy.” Ordinary meaning exceeds datasets of common usage — even very large ones. Second, dictionary and legal corpus linguistics verdicts diverge dramatically from each other. Part of that divergence is explained by the finding that broad dictionary definitions tend to direct interpreters to extensive interpretations, while data of common usage tends to point interpreters to more prototypical cases. This suggests two different criteria that are often relevant in interpretation: a more extensive criterion and a more narrow, prototypical criterion. Although dictionaries and corpus linguistics might, in some cases, help us identify these criteria, a hard legal-philosophical question remains: Which of these two criteria should guide the interpretation of terms and phrases in legal texts? Insofar as there is no compelling case to prefer one, the results suggest that dictionary definitions, legal corpus linguistics, or even other more scientific measures of meaning may not be equipped in principle to deliver simple and unequivocal answers to inquiries about the so-called “ordinary meaning” of legal texts

What constitutes a “good” life—not necessarily a morally good life, but a life that is good for the person who lived it? In response to this question of “well-being," philosophers have offered three significant answers: A good life is one in which a person can satisfy their desires (“Desire-Satisfaction” or “Preferentism”), one that includes certain good features (“Objectivism”), or one in which pleasurable states dominate or outweigh painful ones (“Hedonism”). To adjudicate among these competing theories, moral philosophers traditionally gather data from thought experiments and intuition. In this chapter, we supplement that traditional approach with a pair of experimental studies that examine whether the three theories reflect laypeople’s intuitions about well-being. The empirical studies yield two primary findings. First, they provide evidence for lay "well-being pluralism": laypeople treat desire satisfaction, positive objective conditions, and happiness as all constitutive of well-being. Second, the studies provide evidence of "hedonic dominance": laypeople evaluate an individual’s happiness as more important to an individual’s overall well-being than desire satisfaction or objective conditions.

Despite pervasive variation in the content of laws, legal theorists and anthropologists have argued that laws share certain abstract features and even speculated that law may be a human universal. In the present report, we evaluate this thesis through an experiment administered in 11 different countries. Are there cross‐cultural principles of law? In a between‐subjects design, participants (N = 3,054) were asked whether there could be laws that violate certain procedural principles (e.g., laws applied retrospectively or unintelligible laws), and also whether there are any such laws. Confirming our preregistered prediction, people reported that such laws cannot exist, but also (paradoxically) that there are such laws. These results document cross‐culturally and –linguistically robust beliefs about the concept of law which defy people's grasp of how legal systems function in practice.

“Experimental jurisprudence” draws on empirical data to inform questions typically associated with jurisprudence or legal theory. Scholars in this flourishing movement conduct empirical studies about a variety of legal language and concepts. Despite the movement’s growth, its justification is still opaque. Jurisprudence is the study of deep and longstanding theoretical questions about law’s nature, but “experimental jurisprudence,” it might seem, simply surveys laypeople. This Article elaborates and defends experimental jurisprudence. Experimental jurisprudence, appropriately understood, is not only consistent with traditional jurisprudence; it is an essential branch of it.

Exploring issues ranging from the metaphysical to the moral and legal, a team of esteemed contributors bring together some of the most important and cutting-edge findings in experimental philosophy of the self to address longstanding philosophical questions about personal identity, such as: What makes us today the same person as our childhood and future selves? Can certain changes transform us into a different person? Do our everyday moral practices presuppose a false account of who we are? Chapters offer a survey of recent empirical work and foster dialogue between experimental and traditional philosophical approaches to identity, covering the moral self, dual character concepts, true self, transformative experience and the identity conditions collective entities. With novel experiments and thought-provoking applications to practical concerns including law, immigration, bioethics and politics, this collection highlights the value and implications of empirical work on personal identity.

The personal identity relation is of great interest to philosophers, who often consider fictional scenarios to test what features seem to make persons persist through time. But often real examples of neuroscientific interest also provide important tests of personal identity. One such example is the case of Phineas Gage – or at least the story often told about Phineas Gage. Many cite Gage’s story as example of severed personal identity; Phineas underwent such a tremendous change that Gage “survived as a different man.” I discuss a recent empirical finding about judgments about this hypothetical. It is not just the magnitude of the change that affects identity judgment; it is also the negative direction of the change. I present an experiment suggesting that direction of change also affects neuroethical judgments. I conclude we should consider carefully the way in which improvements and deteriorations affect attributions of personal identity. This is particularly important since a number of the most crucial neuroethical decisions involve varieties of cognitive enhancements or deteriorations.

The Twin Earth thought experiment invites us to consider a liquid that has all of the superficial properties associated with water (clear, potable, etc.) but has entirely different deeper causal properties (composed of “XYZ” rather than of H2O). Debates about natural kind concepts have sought to accommodate an apparent fact about ordinary people's judgments: Intuitively, the Twin Earth liquid is not water. We present results showing that people do not have this intuition. Instead, people tend to judge that there is a sense in which the liquid is not water but also a sense in which it is water.

One popular conception of natural theology holds that certain purely rational arguments are insulated from empirical inquiry and independently establish conclusions that provide evidence, justification, or proof of God’s existence. Yet, some raise suspicions that philosophers and theologians’ personal religious beliefs inappropriately affect these kinds of arguments. I present an experimental test of whether philosophers and theologians’ argument analysis is influenced by religious commitments. The empirical findings suggest religious belief affects philosophical analysis and offer a challenge to theists and atheists, alike: reevaluate the scope of natural theology’s conclusions or acknowledge and begin to address the influence of religious belief.

The Twin Earth thought experiment invites us to consider a liquid that has all of the superficial properties associated with water (clear, potable, etc.) but has entirely different deeper causal properties (composed of “XYZ” rather than of H2O). Although this thought experiment was originally introduced to illuminate questions in the theory of reference, it has also played a crucial role in empirically informed debates within the philosophy of psychology about people’s ordinary natural kind concepts. Those debates have sought to accommodate an apparent fact about ordinary people’s judgments: Intuitively, the Twin Earth liquid is not water. We present results from four experiments showing that people do not, in fact, have this intuition. Instead, people tend to have the intuition that there is a sense in which the liquid is not water but also a sense in which it is water. We explore the implications of this finding for debates about theories of natural kind concepts, arguing that it supports views positing two distinct criteria for membership in natural kind categories – one based on deeper causal properties, the other based on superficial, observable properties.