Timeline of type B physicalism

This is a timeline of Type-B physicalism, the view in philosophy of mind holding that phenomenal consciousness is identical to physical states as a matter of a posteriori metaphysical necessity, even though this identity is not knowable a priori. The timeline traces the position from its mid-century origins in identity theory (Place, Smart, Lewis) through Chalmers' 1999 formalization of the Type-A/Type-B distinction, the phenomenal concept strategy, and ongoing debates over the explanatory gap.

Sample questions

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Big picture

Time period	Development summary	More details

Full timeline

Year	Event type	Details
1956	Publication	British philosopher U. T. Place publishes "Is Consciousness a Brain Process?" in the British Journal of Psychology, arguing against both behaviorism and dualism that consciousness should instead be identified with a pattern of brain activity — an influential statement of identity theory, also known as "Australian materialism." Distinguishing the "is" of definition from the "is" of composition, Place argues that "consciousness is a process in the brain" is neither self-contradictory nor self-evident but a reasonable scientific hypothesis, analogous to "lightning is a motion of electric charges."
1959	Publication	Australian philosopher J. J. C. Smart publishes "Sensations and Brain Processes" in the Philosophical Review (Vol. 68, No. 2), defending the mind-brain identity theory by arguing that sensations are identical with brain processes — explicitly framing the paper as an attempt to present Place's 1956 thesis "in a more nearly unobjectionable form" and to answer objections Place had not considered. Smart introduces the crucial notion of "topic-neutral" language: when someone says "I have a yellowish-orange after-image" they are saying something like "there is something going on which is like what goes on when I see an orange," using quasi-logical words that are neutral between dualist and materialist metaphysics, explaining how sensations can be brain processes without the sensation statement meaning the same as the brain-process statement. Smart's term for sensations viewed as lying outside the physicalist picture — "nomological danglers" (borrowed from Feigl) — became one of the most quoted phrases in the philosophy of mind literature.
1966	Publication	American philosopher David Lewis publishes "An Argument for the Identity Theory" in the Journal of Philosophy, arguing — more strongly than Place or Smart — that anyone who accepts the materialistic working hypothesis that all physical phenomena have purely physical explanations is not merely *free* to accept identity theory but is *compelled* to: the definitive characteristic of any experience is its causal role, and if materialists believe those causal roles belong to physical states, then experiences simply are those physical states. The causal-role definition of experience introduced here becomes the direct foundation of Lewis's later analytic functionalism in "Psychophysical and Theoretical Identifications" (1972, below).
1967	Publication	American philosopher Hilary Putnam publishes "Psychological Predicates" in W. H. Capitan and D. D. Merrill's edited volume Art, Mind, and Religion (later reprinted as "The Nature of Mental States" in Putnam's Mind, Language, and Reality), introducing the multiple realizability argument against type-identity theory: pain cannot be identical to any single physical-chemical brain state because the same psychological predicate applies to organisms with radically different physiologies — a mammal and an octopus can both feel pain despite having no shared brain-state type, since (Putnam notes) their eyes evolved convergently from entirely different cell types despite performing the same function. Putnam proposes instead that pain is a "functional state of the whole organism," defined by its causal role within a system's Turing Machine-style functional organization rather than by its physical realization, and argues this hypothesis is superior to both the brain-state theory and behaviorist "behavior disposition" accounts (the latter cannot specify the relevant disposition except by circularly invoking pain itself). Putnam also directly rebuts J. J. C. Smart's objection that non-physical states are unintelligible, noting that functional states are neither mental nor physical per se. This multiple realizability argument would become the central challenge motivating the shift from strict type-identity theory toward the causal-role and functionalist analyses developed by David Armstrong (1968, above) and David Lewis (1970–72, below).
1968	Publication	David Armstrong publishes A Materialist Theory of the Mind, developing a sophisticated scientific materialism that would influence later Type-B approaches.
1970	Publication	American philosopher David Lewis publishes "How to Define Theoretical Terms" in the Journal of Philosophy (Vol. 67, No. 13), providing the formal apparatus later applied to psychophysical identifications — arguing that theoretical terms introduced by a new theory T are definable as the occupants of the unique causal roles specified by T, and that when a reducing theory shows what occupies those roles, the bridge laws connecting mental and physical states follow as deductive consequences rather than voluntary posits made for parsimony. This is the logical machinery that makes Lewis's 1972 "Psychophysical and Theoretical Identifications" (below) possible: the 1970 paper introduces the general method, the 1972 paper applies it specifically to folk psychology and neural states.
1972	Publication	David Lewis publishes "Psychophysical and Theoretical Identifications", arguing that psychophysical identities should be understood as implied by the theories that make them possible rather than posited independently, refining the Ramsey-style functional-definition approach from his 1966 and 1970 papers into the form most often cited by later Type-B physicalists.
1974	Thought experiment	Thomas Nagel publishes "What Is It Like to Be a Bat?", arguing that subjective experience presents a special explanatory challenge for physicalism — any reductive account of mind seems to leave out the subjective "what it is like" character of experience — and helping motivate later Type-B responses that try to preserve physicalism without denying this subjective character.
1980	Thought experiment	Saul Kripke publishes Naming and Necessity in book form, arguing that identities such as "pain = C-fiber firing" appear contingent, creating a major challenge for materialist theories of mind.
1980	Publication	David Lewis publishes "Mad Pain and Martian Pain", defending functionalist and physicalist approaches to mental states.
1982	Knowledge argument	Frank Jackson introduces the Mary thought experiment in "Epiphenomenal Qualia", arguing that physical knowledge may be incomplete.
1983	Publication	Joseph Levine publishes "Materialism and Qualia: The Explanatory Gap", coining the term "explanatory gap" and posing a central challenge that later Type-B physicalists would need to answer.
1989	Publication	Colin McGinn publishes "Can We Solve the Mind–Body Problem?", arguing that the explanatory gap reflects a permanent limitation of human cognitive faculties ("cognitive closure") rather than evidence against physicalism — a naturalistic but non-Type-B response to the gap (closer to what Chalmers would later classify as Type-C materialism) that nonetheless sharpened the explanatory-gap debate Type-B physicalists needed to answer.
1990	Publication	Brian Loar publishes "Phenomenal States", arguing that the explanatory gap results from special concepts rather than non-physical properties, an early statement of the phenomenal concepts strategy.
1993	Publication	David Papineau publishes "Physicalism, Consciousness, and the Antipathetic Fallacy", introducing the "antipathetic fallacy" — the idea that phenomenal and physical concepts of the same state feel intuitively distinct even though they refer to the same thing, producing an illusion of an explanatory gap — the core idea underlying all of Papineau's later Type-B defenses.
1993	Publication	David Papineau publishes Philosophical Naturalism, defending the view that consciousness, meaning, and knowledge can all be accommodated within a naturalist, physicalist worldview, and diagnosing the intuition that consciousness is non-physical as a confusion arising from the special structure of human imagination — the book-length companion to his AJP paper on the antipathetic fallacy published the same year.
1993	Publication	David Chalmers completes his PhD dissertation Toward a Theory of Consciousness at Indiana University, developing the supervenience-based framework and conceivability arguments that consciousness is not logically supervenient on the physical — the direct precursor to The Conscious Mind and the source of the conceivability arguments that would become the principal target of later Type-B responses.
1994	Publication	David Lewis publishes "Reduction of Mind", defending psychophysical reduction while emphasizing the distinction between conceptual and metaphysical necessity — Lewis explicitly addresses Frank Jackson's knowledge argument here, holding that Mary gains new abilities upon seeing color rather than new factual information, a key move in the Type-B response to the knowledge argument.
1995	Publication	David Chalmers publishes "Facing Up to the Problem of Consciousness" in the Journal of Consciousness Studies, coining the term "hard problem" and giving the conceivability argument its widely-cited public debut a year before The Conscious Mind.
1996	Classification introduced	David Chalmers publishes The Conscious Mind, setting out the a priori/a posteriori entailment distinction that Chalmers would formally label Type-A and Type-B materialism in his 1999 reply to critics; Chalmers identifies philosophers such as David Lewis and David Armstrong as exemplars of positions that would later be classified as Type-B.
1997	Publication	Brian Loar publishes a revised version of "Phenomenal States" in Ned Block, Owen Flanagan, and Güven Güzeldere's edited volume The Nature of Consciousness, further developing the phenomenal concepts strategy.
1997	Publication	Christopher Hill (philosopher) publishes "Imaginability, Conceivability, Possibility and the Mind-Body Problem", arguing that the apparent conceivability of mind-body separability stems from distinct imaginative faculties (sympathetic versus perceptual imagination) rather than from any genuine metaphysical gap, a response to Kripke's modal argument that would become an influential contribution to the Type-B literature.
1997	Publication	David Chalmers publishes "Moving Forward on the Problem of Consciousness", a lengthy response to 26 commentaries on his 1995 "Facing Up to the Problem of Consciousness", addressing deflationary critiques, non-reductive critiques, and positive proposals, sharpening the target that later phenomenal concept strategies would need to engage.
1998	Publication	Christopher Hill publishes "Chalmers on the Apriority of Modal Knowledge", critiquing the modal-epistemological foundations of Chalmers' anti-materialist argument in The Conscious Mind — a direct challenge that provoked Chalmers to formalize the Type-A/Type-B materialism distinction explicitly in his reply the following year.
1999	Publication	Christopher Hill and Brian McLaughlin publish "There Are Fewer Things in Reality Than Are Dreamt of in Chalmers's Philosophy", part of a four-paper Philosophy and Phenomenological Research symposium on The Conscious Mind that directly provoked Chalmers' reply formalizing the Type-A/Type-B materialism distinction.
1999	Publication	David Chalmers publishes "Materialism and the Metaphysics of Modality" in response to a symposium on The Conscious Mind (including papers by Hill and Brian McLaughlin, Brian Loar, Sydney Shoemaker, and Stephen Yablo), explicitly naming and formalizing the "Type-A materialism" and "Type-B materialism" labels that would define the terminology this timeline uses.
1999	Publication	Ned Block and Robert Stalnaker publish "Conceptual Analysis, Dualism, and the Explanatory Gap", defending physicalism while acknowledging explanatory difficulties and arguing against the requirement that physical theories provide a priori conceptual entailments of phenomenal truths.
1999	Publication	Katalin Balog publishes "Conceivability, Possibility, and the Mind-Body Problem", arguing that Chalmers' zombie conceivability argument is self-undermining because an analogous argument, run "in the mouth of a zombie," would lead to a false conclusion — an influential internal defense of physicalism against conceivability arguments that established Balog as a leading phenomenal-concept-strategy theorist.
2000	Publication	Michael Tye publishes Consciousness, Color, and Content, defending representationalism and treating the explanatory gap as a kind of cognitive illusion rather than evidence of a genuine epistemic or ontological gap — a position that sits ambiguously between Type-A and Type-B materialism depending on how the "cognitive illusion" framing is read.
2001	Publication	David Chalmers and Frank Jackson publish "Conceptual Analysis and Reductive Explanation", arguing that reductive explanation of the phenomenal requires a priori entailment from microphysical truths to phenomenal truths — directly rebutting Ned Block and Robert Stalnaker's 1999 Type-B defense and prompting extensive Type-B physicalist responses on the role of conceptual analysis in resisting the conceivability and explanatory-gap arguments.
2002	Publication	David Papineau publishes Thinking About Consciousness, defending a Type-B physicalist account based on phenomenal concepts.
2005	Publication	Daniel Stoljar publishes "Physicalism and Phenomenal Concepts", dividing the phenomenal concepts strategy into several versions and arguing that none of them succeeds in defending physicalism against anti-physicalist arguments — an early and influential critique of the Type-B approach.
2006	Publication	Daniel Stoljar publishes Ignorance and Imagination: The Epistemic Origin of the Problem of Consciousness, arguing that explanatory gaps arise from our ignorance of relevant physical facts rather than implying dualism — an epistemic variant adjacent to, but distinct from, mainstream Type-B phenomenal-concept strategies.
2007	Publication	David Papineau publishes "Phenomenal and Perceptual Concepts" in Torin Alter and Sven Walter's edited volume Phenomenal Concepts and Phenomenal Knowledge, extending the comparison between phenomenal and perceptual concepts and directly responding to David Chalmers' argument against the Type-B phenomenal concept strategy.
2007	Publication	David Chalmers publishes "Phenomenal Concepts and the Explanatory Gap" in the same volume, presenting a "master argument" intended to show that no version of the phenomenal concept strategy can simultaneously explain our epistemic situation regarding consciousness and be physically explicable itself — directly targeting the Type-B approaches defended in Papineau's chapter.
2007	Publication	Torin Alter publishes "Does Representationalism Undermine the Knowledge Argument?" in the same volume, examining whether representationalist theories of consciousness (such as Tye's) can answer Jackson's knowledge argument without appeal to phenomenal concepts.
2008	Publication	British philosopher Robert Kirk (philosopher) publishes "Physicalism and Phenomenal Consciousness" in Teorema (Vol. 27, No. 3, a special issue on "La conciencia fenoménica y el naturalismo contemporáneo" / "Phenomenal Consciousness and Contemporary Naturalism"), addressing the influential anti-physicalist argument from transposed and absent qualia: (1) if physicalism is true, transposed and absent qualia are impossible; (2) transposed and absent qualia are possible; (3) therefore physicalism is false. Kirk argues that physicalism commits its defenders to a "strict implication thesis" — the physical facts strictly imply all the mental facts — under a strong reading of premise (1), and that neither classical identity theory nor a posteriori (Type-B) physicalism escapes this commitment, contrary to what their proponents often suppose; defeating the argument therefore requires directly disproving premise (2), a task Kirk does not attempt in this paper. He further argues, however, that strict implication does not itself require analytic (a priori) links between the physical and the mental, so those who demand full "transparency" between physical and phenomenal concepts are imposing an unnecessary and overly strong requirement on physicalists.
2008	Publication	Janet Levin publishes "Taking Type-B Materialism Seriously" in Mind & Language (Vol. 23, No. 4, pp. 402–425), defending Type-B materialism against anti-physicalist objections (grounded in the conceivability of zombies, Mary's ignorance, and the explanatory gap) by arguing that these objections share a common flaw: they fail to take the central, distinctive features of Type-B materialism — namely its claim that phenomenal concepts have no a priori connections to physical or functional concepts, despite phenomenal states being necessarily identical to physical states — sufficiently seriously. Levin closes by conceding that Type-B materialism raises further questions of its own, and suggests that what stands in the way of a fully adequate naturalistic account of phenomenal states may be exactly this propensity among philosophers to not take Type-B materialism as seriously as it deserves — a preview of the argument she would return to a decade later in her 2018 "Once More Unto the Breach" (above/below).
2009	Publication	Katalin Balog publishes "Phenomenal Concepts" in The Oxford Handbook of Philosophy of Mind, surveying the phenomenal concept strategy and developing a "constitutional account" on which phenomenal concept tokens are partly constituted by the very experiences they refer to.
2009	Publication	Sam Coleman (Birkbeck College, University of London) publishes "Chalmers's Master Argument and Type Bb Physicalism," responding directly to David Chalmers' 2007 dilemmatic "master argument" against every version of the phenomenal concept strategy (above). Chalmers' argument forces phenomenal concept strategists to choose between two unpalatable "horns": either treat phenomenal concepts as themselves physically explicable (horn a), which Chalmers argues undermines their ability to explain the epistemic situation regarding consciousness, or deny they are physically explicable (horn b), which undermines physicalism itself. Coleman explores and defends a position he dubs "Type Bb" — for Type-B physicalists willing to embrace horn b of the dilemma — and argues that Chalmers fails to demonstrate any genuine incoherence in the position of a Type-B physicalist who takes this route while still relying on the phenomenal concept strategy.
2010	Publication	Daniel Stoljar publishes Physicalism, a systematic introduction to the doctrine covering its history, formulation, and the central challenges from conceivability and the explanatory gap, situating his own epistemic approach within the wider physicalist landscape including Type-B responses.
2011	Publication	David Papineau publishes "Phenomenal Concepts and the Private Language Argument", examining whether positing phenomenal concepts is consistent with Wittgenstein's private language argument, and concluding that it is not — a self-critical stress-test of his own Type-B framework from inside the camp.
2012	Publication	Katalin Balog publishes "In Defense of the Phenomenal Concept Strategy", directly responding to David Chalmers' 2007 master argument and defending a "constitutional" account in which phenomenal concepts are constituted by the very experiences they pick out, explaining the appearance of an epistemic gap without requiring any non-physical properties.
2012	Publication	Janet Levin (University of Southern California) publishes "Do Conceivability Arguments against Physicalism Beg the Question?" in Philosophical Topics (Vol. 40, No. 2, "Consciousness" special issue, pp. 71–89), examining an increasingly popular Type-B response to conceivability arguments (such as Chalmers' zombie argument and Kripke's modal argument): the claim that these arguments' conceivability premises beg the question, since one's ability to conceive of zombies or disembodied minds depends entirely on one's antecedent theoretical commitments about the nature of consciousness, and so cannot legitimately be used to draw conclusions about whether conscious experiences could be physical. Rather than simply endorsing this popular "question-begging" response, Levin raises critical questions about various versions of it and argues that physicalists have more promising ways available to them for disarming conceivability arguments against physicalism.
2012 (January 15)	Publication	Adrian Boutel (Christ's College, University of Cambridge) publishes "How to be a type-C physicalist" in Philosophical Studies (Vol. 164, No. 2, pp. 301–320), defending a version of physicalism that reconciles the "a priori entailment thesis" (APET) — the claim that the complete truths of physics imply every other truth a priori, such that a demon with only complete physical knowledge could deduce every truth about the world ("cosmic hermeneutics") — with "analytic independence," the popular Type-B physicalist explanation for the apparent epistemic gap between phenomenal and physical truths, which is generally taken to be incompatible with APET since the demon's deductions seem to presuppose analytic connections between physical and phenomenal terms that Type-B physicalists deny exist. Boutel argues that implications from the complete truths of physics to phenomenal truths cannot be a posteriori in the Kripke style, since (by the physicalist's own lights) the complete truths of physics already fix any relevant a posteriori facts about the reference of phenomenal terms; he then shows how the physicalist can exploit this fixing of reference to deduce that phenomenal and physical terms co-refer, opening the way for a "Type-C" physicalism that accepts in-principle a priori deducibility while still appealing to Type-B-style analytic independence to explain why non-demons like us find phenomenal-physical connections impossible to see a priori in practice.
2013	Publication	Robert J. Howell publishes Consciousness and the Limits of Objectivity: The Case for Subjective Physicalism (Oxford University Press, 190pp.), defending a version of Type-B physicalism he calls "subjective physicalism": consciousness is wholly physical, but cannot be fully captured by any objective, third-person theory, because it can only be known "from the inside" via acquaintance. Howell defines physicalism using "Trans-World Disposition Sets" — physical properties are those whose causal/dispositional profile is exhaustively characterizable in terms of spatial and temporal implications — and argues that phenomenal properties, while physical, have an irreducibly subjective "aspect" that keeps a complete, objective physical theory from being what Howell calls "complete" in his technical sense (able to rule out all epistemically possible scenarios, such as zombies or spectrum inversion). Howell frames responses to Jackson's knowledge argument as splitting into "hardliners" (who deny Mary learns anything new, i.e. Type-A physicalists) and "epistemicists" (who grant she learns something epistemically significant but deny any metaphysical gap, i.e. Type-B physicalists), and situates his own view firmly in the latter camp while explicitly separating epistemic from metaphysical considerations. He argues subjective physicalism is preferable to eliminativism as the consequence physicalists should draw from taking consciousness seriously, while resisting the further step (which he associates with Russellian monism) of treating microphenomenal properties as fundamental and causally basic.
2014 (September 6)	Publication	Brian Tomasik publishes "Is There A Hard Problem of Consciousness?" on his website reducing-suffering.org (last substantively updated 21 June 2018), a long essay defending Type-A physicalism against Type-B by arguing that the "zombic hunch" — the intuition that phenomenal consciousness could be absent from a physical duplicate — is best explained as one more case of human intuition failing in a predictable, patterned way, analogous to optical illusions or pre-relativistic intuitions about absolute time. Tomasik argues Type-B physicalism amounts to disguised property dualism (following an argument he attributes to Chalmers), and poses a dilemma against it: if qualia supervene purely on functional organization, physical systems admit multiple equally valid functional interpretations with no fact of the matter about which one is "the" conscious interpretation; but if qualia also depend on some further non-functional element (as in Ned Block's "biological" view), that element does no causal work and renders qualia epiphenomenal. He proposes an alternative "acquaintance knowledge" framework — following William James and Earl Conee — on which phenomenal experience is not propositional knowledge that could in principle be third-personally derived, but a first-person mode of being identical to being the physical system in question, dissolving rather than bridging the explanatory gap. The piece also engages directly with Sam Coleman's "Type Bb" response (above) to Chalmers' master argument, noting that Type-A and Type-B positions remain mutually self-consistent once one has settled whether to accept or reject the initial "zombic hunch."
2017	Publication	Brian P. McLaughlin publishes "Type Materialism for Phenomenal Consciousness" in Susan Schneider and Max Velmans' edited The Blackwell Companion to Consciousness (2nd edition), giving a handbook-level defense of Type-B materialism as one of the principal physicalist responses to the hard problem — McLaughlin's return to the topic nearly two decades after his 1999 paper with Hill.
2017	Publication	American philosopher Helen Yetter-Chappell (University of York / University of Miami) publishes "Dissolving Type-B Physicalism" in Philosophical Perspectives (Vol. 31, "Philosophy of Mind" themed issue; first published online 25 April 2018), arguing directly against Type-B physicalism rather than merely defending Type-A: she constructs a hypothetical agent ("Mary*") who has complete general physical knowledge, possesses genuine phenomenal concepts (meeting the constitutional theory's own criteria, as developed by Katalin Balog and others), and yet is psychologically "wired" to immediately recognize that her phenomenal concepts and physical concepts corefer — deriving phenomenal-physical identities a priori rather than a posteriori. Since physicalists must grant that such an agent's low-level cognitive architecture is a complete physical description of a possible mind, and that this agent would find no epistemic gap, Yetter-Chappell concludes there is no ideal epistemic gap between the phenomenal and the physical: humans find such a gap only because of a contingent, seemingly non-adaptive quirk of human psychology, not because phenomenal concepts are intrinsically disconnected from physical concepts. She extends the argument beyond the constitutional theory to indexical (Perry 2001) and direct reference (Levin 2007, Tye 2003) theories of phenomenal concepts, arguing all three fail to secure an ideal gap for the same underlying reason. The paper's positive upshot is a new "Type-A phenomenal concept strategy" that keeps the intuitive payoffs Type-B physicalists wanted (that Mary would be fooled by a blue banana, that zombies would still seem conceivable to us) while denying that any of this reflects a genuine metaphysical or ideal epistemic gap.
2018	Publication	Janet Levin publishes "Once More Unto the Breach: Type B Physicalism, Phenomenal Concepts, and the Epistemic Gap", arguing that physicalists have lost confidence in Type-B physicalism too readily and have retreated to less promising defenses, when in fact the resources of phenomenal-concept-based Type-B physicalism remain underestimated and the relevant battles have "already been won".
2020	Publication	Daniel Stoljar publishes "The Epistemic Approach to the Problem of Consciousness" in Uriah Kriegel's edited The Oxford Handbook of the Philosophy of Consciousness, restating his epistemic view that explanatory limitations regarding consciousness reflect contingent ignorance of relevant physical facts rather than any metaphysical gap — a view closer to Type-C materialism and mysterianism than to the mainstream phenomenal-concept-strategy form of Type-B physicalism.
2020	Publication	Joseph Levine publishes "A Posteriori Physicalism: Type-B Materialism and the Explanatory Gap" as Chapter 18 in Uriah Kriegel's edited The Oxford Handbook of the Philosophy of Consciousness (pp. 387–404; published online 9 July 2020), revisiting the explanatory gap he named in his own 1983 paper (above) and arguing for a notable shift in position: whereas Levine (1998, 2001) had held that the conceivability of zombies reveals a genuine explanatory gap between the physical and the mental but that there remained good reason to adopt materialism regardless, this chapter sides with the more skeptical view of Levine (2014), arguing that the persistence of the explanatory gap itself licenses an inference to the best explanation — namely, that the gap's existence and persistence is best explained by there being a genuine underlying metaphysical gap between the physical and the phenomenal, not merely an epistemic one. Levine lays out and rejects the standard argument that materialism must be abandoned simply because zombies are conceivable, and also rejects Type-B materialists' related claim that the explanatory gap poses no real problem for physicalism, arguing that the inference to the best explanation survives this defense.
2021	Publication	American philosopher Helen Yetter-Chappell publishes "Dissolving Type-B Physicalism" in Philosophical Perspectives, arguing directly against Type-B physicalism rather than merely defending Type-A: she constructs a hypothetical agent ("Mary*") who has complete general physical knowledge, possesses genuine phenomenal concepts (meeting the constitutional theory's own criteria, as developed by Katalin Balog and others), and yet is psychologically "wired" to immediately recognize that her phenomenal concepts and physical concepts corefer — deriving phenomenal-physical identities a priori rather than a posteriori. Since physicalists must grant that such an agent's low-level cognitive architecture is a complete physical description of a possible mind, and that this agent would find no epistemic gap, Yetter-Chappell concludes there is no ideal epistemic gap between the phenomenal and the physical: humans find such a gap only because of a contingent, seemingly non-adaptive quirk of human psychology, not because phenomenal concepts are intrinsically disconnected from physical concepts. She extends the argument beyond the constitutional theory to indexical (Perry 2001) and direct reference (Levin 2007, Tye 2003) theories of phenomenal concepts, arguing all three fail to secure an ideal gap for the same underlying reason. The paper's positive upshot is a new "Type-A phenomenal concept strategy" that keeps the intuitive payoffs Type-B physicalists wanted (that Mary would be fooled by a blue banana, that zombies would still seem conceivable to us) while denying that any of this reflects a genuine metaphysical or ideal epistemic gap.
2022 (June 16)	Publication	Philosopher David Chalmers, interviewed by Robert Lawrence Kuhn for the Closer to Truth series, walks a popular audience through his own Type-A/Type-B/Type-C classification of materialism (introduced in 1999, above) before rejecting all three: he characterizes Type-A materialism as denying that consciousness exists at all (eliminativism), restates Type-B materialism as holding that consciousness just is a brain process even though our concepts of the two remain distinct, and describes Type-C materialism as treating the hard problem as a currently unsolved but eventually science-resolvable puzzle. Having rejected each variety of materialism, Chalmers argues that consciousness should instead be treated as a fundamental category of reality in its own right, sketching further possibilities on which consciousness is either a causally inert epiphenomenon or has genuine causal impact on the physical world, possibly mediated by quantum mechanics.
2023	Publication	Marcelino Botin (University of Barcelona) publishes "Russellian Physicalists get our phenomenal concepts wrong" in Philosophical Studies (Vol. 180, pp. 1829–1848), defending Type-B physicalism by contrasting its resources with those of the rising alternative, Russellian physicalism (RP). Botin applies Philip Goff's 2011 "revelation challenge" — the argument that a phenomenal concept must be transparent, translucent, or opaque with respect to its referent's essential properties, and that none of these options is available to a physicalist who also wants realism about consciousness — to both views, and argues it is survivable for Type-B physicalism (which can hold that phenomenal concepts are translucent, revealing the essence of experience but only under a phenomenal rather than physical characterization, per Katalin Balog's constitutional account) but fatal for Russellian physicalism, which is committed to the further claim that phenomenal-physical identities are knowable a priori given a complete account of intrinsic physical properties — a commitment the phenomenal concept strategy's account of conceptual isolation cannot satisfy. Botin further argues that Type-B physicalism does not need to borrow any of Russellian physicalism's machinery (postulating inscrutable intrinsic properties) to explain the hallmark features attributed to consciousness — ineffability, irreducibility, and (apparent) intrinsicness — since the phenomenal concept strategy already accounts for these via conceptual isolation and constitutional reference.
2024	Publication	Christopher Devlin Brown and David Papineau publish "Illusionism and A Posteriori Physicalism; No Fact of the Matter" in the Journal of Consciousness Studies, arguing that the apparent dispute between illusionism (the view that phenomenal consciousness, in the strong sense implying non-physical properties, does not exist) and a posteriori (Type-B) physicalism is merely a definitional dispute rather than a substantive disagreement. The authors argue that whether to treat "phenomenal consciousness" as a concept to be eliminated (per illusionism) or reconstructed with a weaker, physically acceptable meaning (per Type-B physicalism, following Papineau's own long-standing phenomenal concept strategy) is a judgment call comparable to other cases in the history of science and philosophy where a term either survived with a revised meaning (as with "planet" or "star") or was abandoned outright (as with "phlogiston" or "witch") once its originally assumed properties turned out not to exist. On their view, both camps ultimately agree on the underlying physical facts and disagree only about which linguistic and conceptual packaging is most useful.
2024	Publication	Marcelino Botin publishes "A posteriori Russellian physicalism: a new solution to the meta-problem of consciousness" in The Philosophical Quarterly (published online 22 October 2024), extending his 2023 critique of Russellian physicalism (above) into a positive proposal. Botin argues that neither of the two leading physicalist realist positions — orthodox Russellian physicalism nor Type-B physicalism — can adequately solve Chalmers' "meta-problem of consciousness" (the problem of explaining why we believe there is a hard problem of consciousness in the first place). He then introduces "a posteriori Russellian physicalism," a hybrid view combining Russellian monism's appeal to intrinsic physical properties with the phenomenal concept strategy characteristic of Type-B physicalism, and argues this hybrid overcomes the specific difficulties that beset each view taken alone. Botin's stated aim is to show that physicalists need not retreat to illusionism, since a physicalist realist solution to the meta-problem remains available via this Russellian phenomenal-concept-strategy hybrid.
2024 (September 1)	Publication	Will Moorfoot publishes "Type-R physicalism" in Philosophical Psychology (Vol. 39, Issue 2, pp. 292–317; received 20 Oct 2023, accepted 18 Aug 2024, published online 1 Sep 2024), introducing a category of physicalism distinct from Chalmers' Type-A, Type-B, and Type-C: the "reconciliatory response" to the conceivability argument, which grants that zombies are metaphysically possible but denies this refutes physicalism. Moorfoot develops "stochastic ground physicalism" (SGP) as a concrete version of Type-R physicalism, on which phenomenal facts are stochastically (rather than deterministically) grounded in physical facts — the physical facts fix a probability distribution over possible phenomenal outcomes without necessitating any single one, which lets phenomenal facts count as physical (satisfying "Physicality") while remaining modally separable from their physical grounds (satisfying the metaphysical possibility of zombies). Moorfoot explicitly contrasts Type-R with Type-B: whereas Type-B physicalists reject the entailment from conceivability to possibility by positing "strong necessities" and accepting a resulting "modal dualism" between logical and metaphysical modality, Type-R physicalists reject the conceivability argument's final premise instead (that zombie-possibility entails physicalism's falsity), letting them jointly accept a thick, non-functionalist conception of consciousness, the transparency of phenomenal concepts, and full modal rationalism — a combination of resources Moorfoot argues is unavailable to Type-A, Type-B, or Type-C physicalists individually.
2025	Publication	Peng Zhou (Chinese University of Hong Kong) publishes "Indicating without revealing: a posteriori physicalism and the new challenge" in Synthese (Vol. 206, article no. 91; received 25 Nov 2024, accepted 7 Jul 2025, published online 6 Aug 2025), addressing Philip Goff's "New Challenge" against a posteriori (Type-B) physicalism, which argues that Type-B physicalism cannot do justice to the intuition that phenomenal concepts have a substantial, essence-revealing content without thereby violating the a posteriori status of phenomenal-physical identity claims. After surveying and rejecting the three existing Type-B responses to Goff's argument — radical opacity (Papineau, McLaughlin), soft translucency (Levin, Diaz-Leon, Schroer), and dual carving (including recent defenses by Janet Levin (2019, above) and D. Gene Witmer) — Zhou proposes a novel reply: phenomenal concepts have substantial contents in the sense of being "essence-indicating" (providing conditions that would partly or fully constitute the referent's essence) without their reference being determined by satisfaction of those conditions, so that a phenomenal concept can refer to a physical/functional property even though that property does not satisfy the concept's phenomenal content. Zhou acknowledges that this "essence-indicating without essence-revealing" solution places Type-B physicalism close to illusionism, potentially supporting a "unification thesis" recently argued for by Christopher Devlin Brown and David Papineau (2024, above/below) and by Takuya Niikawa (2021), on which the disagreement between a posteriori physicalism and illusionism is largely terminological.
2026 (April 8)	Publication	Philosopher and science communicator Phil Halper (Skydivephil) releases the documentary-style video "Consciousness: Philosophers & Neuroscientists Defend Physicalism" on YouTube, featuring interviews with philosophers and neuroscientists making the case for physicalism, including Robert Kirk and Frank Jackson — historically influential sources of anti-physicalist arguments (Kirk's zombie/conceivability arguments and Jackson's 1982 knowledge argument, above) — both now presented as having "turned to physicalism," alongside Ned Block, David Papineau, Richard Brown, Ken Williford, and neuroscientists Karl Friston, Anil Seth, and Marc Solms. The video addresses standard anti-physicalist arguments (the causal closure argument for physicalism, the zombie argument, Mary's Room, the hard problem, and empirical challenges from near-death and out-of-body experiences) and includes a segment specifically on "the revelation thesis," directly engaging the Type-B-relevant "New Challenge" debate (Goff, Zhou 2025, above) about whether phenomenal concepts reveal the essence of their referents.
2026 (June 28)	Publication	American computer scientist and philosopher Jessica Taylor ("jessicata") publishes "Powerful qualities in type B physicalism" on LessWrong, arguing that Type-B physicalism combines naturally with John Heil's "powerful qualities" (PQ) theory of properties, on which every intrinsic property is simultaneously qualitative and dispositional (redness just is a light-reflectance disposition, viewed under a different mode of presentation) rather than qualities and dispositions being separate "aspects." Taylor argues this pairing does three things for Type-B physicalism: it de-ad-hocs the phenomenal concept strategy by treating phenomenal concepts as a special case of the broader category of qualitative concepts (rather than positing them as sui generis "direct demonstrative"/"quotational" concepts, per Katalin Balog and others); it motivates treating "phenomenally conscious" itself as a secondary qualitative concept, co-referring with some dispositional concept such as Ned Block's "access consciousness," which in turn supports positing unconscious qualities (neural states that would be qualia-bearing if attended to, but currently aren't); and it highlights a structural parallel to debates in the metaphysics of perception, illustrated via a thought experiment about a hypothetical world of "direct realist" philosophers who locate secondary qualities like color in external objects rather than in the mind and face an equivalent explanatory-gap debate about color. Taylor credits Henry Taylor (2017, 2024) with first noting the concordance between Type-B physicalism and powerful qualities theory in the academic literature, and contrasts the resulting position with Russellian monism/panqualityism, illusionism, and analytic functionalism.
2026	Publication	Will Moorfoot publishes "Type-R physicalism" in Philosophical Psychology (Vol. 39, Issue 2, pp. 292–317; received 20 Oct 2023, accepted 18 Aug 2024, published online 1 Sep 2024), introducing a category of physicalism distinct from Chalmers' Type-A, Type-B, and Type-C: the "reconciliatory response" to the conceivability argument, which grants that zombies are metaphysically possible but denies this refutes physicalism. Moorfoot develops "stochastic ground physicalism" (SGP) as a concrete version of Type-R physicalism, on which phenomenal facts are stochastically (rather than deterministically) grounded in physical facts — the physical facts fix a probability distribution over possible phenomenal outcomes without necessitating any single one, which lets phenomenal facts count as physical (satisfying "Physicality") while remaining modally separable from their physical grounds (satisfying the metaphysical possibility of zombies). Moorfoot explicitly contrasts Type-R with Type-B: whereas Type-B physicalists reject the entailment from conceivability to possibility by positing "strong necessities" and accepting a resulting "modal dualism" between logical and metaphysical modality, Type-R physicalists reject the conceivability argument's final premise instead (that zombie-possibility entails physicalism's falsity), letting them jointly accept a thick, non-functionalist conception of consciousness, the transparency of phenomenal concepts, and full modal rationalism — a combination of resources Moorfoot argues is unavailable to Type-A, Type-B, or Type-C physicalists individually.

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See also

• Timeline of type A physicalism
• Timeline of David Chalmers' work on consciousness