Abstract
Thomas Nagel's "What Is It Like to Be a Bat?" remains one of the most influential uses of an animal comparison in twentieth-century philosophy. Echolocation supplies Nagel's imaginative obstacle: a sensory life intelligible enough for us to be confident a bat has a point of view, yet unlike human sensory life enough to resist reconstruction from the outside, making it Nagel's exemplary case for the irreducibility of subjective experience to objective description.
The comparison rests on an assumption that has received far less scrutiny than Nagel's argument itself: why is phenomenal experience, and specifically the phenomenal strangeness of echolocation, the respect in which humans and bats should be compared at all? Humans and bats resemble and differ from one another in indefinitely many respects, and nothing in the instruction to compare them determines which respect matters. Comparative research nonetheless repeatedly privileges a narrow repertoire of presumed thresholds, consciousness, language, tool use, theory of mind, self-recognition, culture, without making explicit why these were selected over any other.
This article calls this the problem of comparative relevance and develops a solution from Living Value Theory. A process constitutive of living recursivity as such cannot function as a test of human distinctiveness merely by being found in a bat; the three zoetic mediations, L1 and L2, and selfrecursivity and nonrecursivity are excluded on these grounds. Relevant comparison begins where the theory does not already settle the distribution: interrecursivity, multimateriality, multisymbolization, and the higher recursive levels these make possible. Read this way, Nagel selected a biologically extraordinary but comparatively unsurprising difference. The more revealing bat lies elsewhere, in questions about bat social life, communication, and accumulation his argument leaves untouched.
I. Nagel's Bat and the Unnoticed Act of Selection
Nagel is not principally interested in bats. He is interested in consciousness and the limits of physicalist reduction, and his central claim is that an organism has conscious experience just in case there is something it is like to be that organism. Bats supply the ideal thought experiment for this claim because there are strong grounds for attributing experience to them while their dominant sensory orientation differs dramatically from ordinary human perception. Nagel asks the reader to imagine flying at dusk, hanging upside down, and navigating by interpreting reflected ultrasonic signals, then points out that this imaginative exercise, however vividly performed, does not deliver what bat experience is actually like for a bat. Nothing here disputes this. The present article does not need to deny the irreducibility of phenomenal experience, and it does not claim that objective description gives direct access to bat phenomenology.
A different question opens up one level above Nagel's own. Why is phenomenal consciousness the relevant dimension along which to compare a human being and a bat? The immediate answer is straightforward: because Nagel is writing about consciousness, which makes his selection legitimate for the argument he is making. But the straightforward answer is also the methodological point. The philosophical question Nagel is asking selects the relevant respect of comparison before the empirical bat ever enters the argument. Echolocation did not announce itself as the intrinsically significant difference between bats and humans. Nagel selected it because it served a prior philosophical purpose, and it served that purpose brilliantly.
Purpose-specific selection becomes ontological privilege with remarkable ease. Consciousness joins a familiar company of capacities repeatedly treated as especially revealing of the boundary between humans and other animals: reason, language, tool use, culture, theory of mind, mirror self-recognition, morality, and explicit awareness of mortality. The literature built around each of these asks whether another species has the selected characteristic. The prior question is asked far less often. Why this characteristic and not another? What would make one difference more revealing than any of the indefinitely many differences a comparison could have selected instead?
This gives the article its governing contrast. Nagel asks what it is like to be a bat. This article asks what is relevant about being a bat when bats and humans are compared. The second question does not replace the first; it exposes the selection that makes the first philosophically useful, and it generalises into a proposition that governs everything that follows: before asking whether humans and bats are alike, one must specify the respect in which likeness would matter.
II. The Problem of Comparative Relevance
Take one human being and one bat. Both are carbon-based organisms, mammals, vertebrates, bilaterally symmetrical, warm-blooded, oxygen-dependent, sexually reproducing, metabolically active, mobile, vulnerable to injury, capable of learning, temporally finite, and dependent on environmental resources. The list could continue for as long as anyone cared to extend it, because there is no natural terminus at which shared properties run out.
The same is true of difference. Humans and bats differ in morphology, locomotion, sensory weighting, body size, reproductive timing, sleep organisation, ecological niche, feeding behaviour, lifespan, vocal production, thermoregulatory strategy, and innumerable further respects, and even a single dimension subdivides without limit on inspection: hearing alone becomes frequency sensitivity, localisation, temporal resolution, neural processing, behavioural use, and developmental acquisition, each comparable separately. There is no exhaustive, neutral inventory of respects from which the important ones simply present themselves.
This is a logical point before it is an empirical one. Nothing is simply similar or different; two entities are similar or different in some respect. A human being resembles a bat more than a stone does with respect to metabolism, while the stone may resemble the human being more closely than the bat does with respect to mass. Comparison is relational and question-dependent by its nature, and every comparative claim necessarily reduces an indefinitely large field of possible relations to a manageable subset. This reduction is unavoidable, and it is not the methodological error. The error is unacknowledged selection: treating the chosen respect as self-evidently important rather than justified in relation to a specified problem.
Appeal to important differences does not resolve this, because importance is not a single property a difference either has or lacks. A difference can be evolutionarily important, phenomenologically important, ethically important, physiologically important, ecologically important, or important to human self-understanding, and these are not interchangeable. A human being's inability to echolocate may be phenomenologically fascinating while comparatively unimportant for explaining cumulative cultural transmission. A bat's ability to enter torpor may be physiologically fundamental to its survival while irrelevant to Nagel's argument about consciousness. Relevance is always relevance to a problem, and a comparison that has not specified the problem has not yet specified what would count as relevant.
This yields the general principle the rest of the article develops. Before asking what similarities and differences exist between two species, comparative inquiry must specify which differences could alter the theoretical claim actually under investigation. Stated this way, comparison stops being trait collection and becomes something closer to hypothesis testing, with a specified stake in the outcome.
III. The Literature Gets Close, But Does Not Formulate the Problem
Some of this ground has already been prepared, though not quite in these terms. Sara Shettleworth's distinction between anthropocentric and ecological programmes in comparative cognition is a major precursor. The anthropocentric programme asks whether nonhuman animals process information in ways resembling human cognition; the ecological programme begins instead from problems that matter within an animal's own way of life, food caching, mate selection, predator avoidance, and asks what cognitive capacities those problems would select for. This is real progress, since it replaces one imported human standard with a standard drawn from the organism's own ecology. But the underlying problem has been relocated rather than resolved. Ecological relevance is itself a criterion of relevance, chosen because it seems like the right one for questions about adaptation. Why should ecological relevance be the privileged standard for every comparative question, including questions, like Nagel's, that are not primarily about adaptation at all?
A related body of work has examined how comparative cognition imports categories, consciousness, culture, theory of mind, from human psychology and then asks whether animal behaviour meets definitions built around those categories. This asks a different question from the one raised here. It asks whether a given performance is comparable once a capacity has already been selected for study. The present argument asks the prior question: why that capacity was selected in the first place, out of the indefinitely many that were available.
A recent bibliometric study of the animal behaviour literature supplies an almost experimental demonstration of relevance selection in practice. Comparing scholarly treatment of tool use and nest construction, both behaviours involving substantial manipulative skill directed at persistent material structures, the study finds that tool-use publications are cited more often, appear more frequently in higher-impact journals, and use more of the vocabulary of intelligence than nest-construction publications do, and that this disparity persists even within studies of the same taxa: great apes and corvids studied for both behaviours show the same skew. Manipulating a stick attracts more cognitive interest than building a structure that keeps offspring alive, and the most plausible explanation is that the stick resembles a prestigious human activity in a way the nest does not. The example is worth returning to, since it shows relevance selection operating on working scientists rather than only on philosophers.
Hans-Johann Glock is the most serious philosophical interlocutor on this question. Glock recognises that species differ from one another in countless ways and asks explicitly which of these differences could constitute what he calls an anthropological difference, substantial enough to mark humans off from other animals in a theoretically interesting sense. His requirements include that the difference be categorical rather than a matter of degree, explanatorily fundamental rather than derivative, and important to human self-understanding, and he arrives at an eventual pluralism, several differences rather than one, that avoids the cruder Rubicon-hunting the tradition is often accused of. But the third requirement carries a tension the other two do not. Importance to human self-understanding is not a neutral criterion for comparative relevance in general; it is close to guaranteed to select language, reason, morality, and technology, precisely because these are the capacities humans already value most highly in themselves. A criterion built this way tells us something real about humans, but it tells us at least as much about what humans value in themselves as it tells us about where the boundary between species actually lies.
Recent multidimensional approaches replace binary presence-or-absence comparisons with profiles across several capacities at once, consciousness, empathy, causal cognition, allowing species to differ without being ranked on one ladder. This is a real advance, since it lets species dissociate rather than forcing them onto a single scale. But it too operates one level below the question asked here. A multidimensional theory of consciousness still presupposes that consciousness, in some number of its dimensions, is what ought to be compared. The dimensions inside the selected domain can be sophisticated while the selection of the domain itself remains unexamined.
Across all of this literature, a common gap emerges. Anthropocentrism has been criticised, binary scoring has been criticised, inappropriate experimental tasks have been criticised, and human-derived definitions have been criticised. What remains under-theorised is the prior act by which some characteristics enter the comparative field at all while indefinitely many others quietly disappear from consideration before the comparison even begins. This is the comparative relevance problem, and it is what the rest of this article addresses directly.
IV. Living Value Theory's Solution: Excluding What the Theory Already Predicts
A useful comparative test should concern something whose distribution the theory being tested has not already settled. If a theory holds that every living being necessarily instantiates some process, discovering that process in a bat cannot distinguish bats from humans within that theory, however striking the discovery is on its own terms; it may reveal a great deal about how bats instantiate the process, but it cannot establish an uncertain boundary, because the theory never treated the boundary as uncertain to begin with.
Living Value Theory's corpus of concepts, on the order of a hundred by current count, gives this principle something concrete to work with. The number is a pragmatic feature of where the theory currently stands rather than a claim that its architecture contains exactly this many irreducible primitives, and it is not important in itself. What matters is that these concepts were not invented as dimensions along which to compare animals. They emerged from the general development of a theory of living recursivity, independently of any particular comparative agenda, and that independence is methodologically valuable in a way a criterion chosen because it makes a comparison interesting is not. The comparative test that follows exposes an existing conceptual architecture to cross-species evidence, rather than selecting characteristics because they make humans or bats look interesting.
Applied to that architecture, three exclusions follow directly. The first concerns the three zoetic mediations. Multisensorial embodiment is excluded because every living being must maintain embodied coordination through some sensory and physiological relation to its surroundings; species differences in sensory configuration can be enormous, as bat echolocation itself demonstrates, but the presence of multisensorial embodiment as such is theoretically expected rather than uncertain. Being-with is excluded for the same reason: living beings develop and continue amid other living beings in radically different forms, but being-with itself is not an open human-animal boundary. Multiversal dwelling is excluded because every living being inhabits a workable world rather than an abstract environment, however much the forms of dwelling vary. These three mediations establish ontological commensurability across the whole of life, and it is precisely because they are universal that they cannot function as discriminating tests.
The second exclusion concerns L1 and L2. Absorbed coordination and felt misalignment vary enormously in their temporality and behavioural expression, but both belong to ordinary living recursivity as such rather than to any uncertain frontier. An octopus struggling with a container, or a bat adjusting its flight path around an unexpected obstacle, can provide spectacular instances of extended L2 disturbance. Neither instance establishes proximity to a uniquely human capacity, because duration and behavioural complexity within L1 and L2 do not by themselves generate a higher recursive level.
The third exclusion concerns selfrecursivity and nonrecursivity. Selfrecursivity is excluded because living continuation necessarily involves a recursive relation to one's own changing states; nonrecursivity is excluded because every living being also coordinates with grounds that are not currently encountered as recursively responsive counterparts. Their concrete forms differ enormously across species. Their presence is not theoretically uncertain.
None of this makes the excluded processes insignificant. Echolocation is biologically extraordinary. Plant phototropism is biologically extraordinary. Octopus chemotactile exploration is biologically extraordinary. Each can be, and is, a central topic within its own area of biology. They are excluded only from this particular test, the identification of theoretically uncertain differences in recursive organisation between humans and other living beings, and exclusion from one test is not a verdict on scientific interest more broadly.
The resulting principle can be stated in its strongest form: relevant species differences begin where theoretically expected commonality ends. More formally, a cross-species comparison is relevant to Living Value Theory only if it concerns a theoretically specified capacity whose distribution across living beings the theory does not already entail.
V. Nagel Chose an Irrelevant Difference
Echolocation can now be reinterpreted through the exclusion principle just developed. It is an extraordinary sensory achievement, and it falls straightforwardly within multisensorial embodiment. A bat emits a call; environmental structures transform the returning signal; the returning echo modifies the bat's ongoing movement; distances change, echoes change in turn, and the trajectory adjusts again. This is an exceptionally vivid instance of recursive embodied coordination, and vividness is exactly what makes it a poor discriminator.
Set echolocation alongside a few other sensory architectures without ranking them: canine olfaction, pit-viper infrared sensitivity, electric-fish electrolocation, the visually dominated coordination of ordinary human perception, the chemotactile exploration of an octopus's suckers. The variety on display is enormous, and if living beings are multisensorially embodied as such, this is exactly the kind of variation evolutionary diversification should be expected to generate. Phenomenal strangeness to a human observer does not make a sensory capacity theoretically privileged; it makes it, at most, unfamiliar to the observer doing the comparing.
None of this is a criticism of Nagel's own argument, and fairness requires saying so plainly. Nagel did not make an elementary mistake. Echolocation is brilliantly chosen for the purpose of challenging reductive accounts of consciousness, precisely because it is exotic enough to defeat easy imaginative identification while remaining tied to an organism whose experience we have every reason to credit. The difficulty appears only when Nagel's bat is asked to do further work it was never built for, becoming a general model for thinking about human-animal difference as such. For Nagel's own problem, echolocation is highly relevant. For the different question of where human and bat recursive organisation actually diverge, it is not, and the same example can carry both verdicts without contradiction, because the two questions specify different problems.
It is worth stating the conclusion in its most provocative form before immediately qualifying it: Nagel chose perhaps the least interesting thing about being a bat. Least interesting here does not mean biologically trivial, and it does not mean phenomenologically uninteresting; echolocation remains remarkable on both counts. It means least discriminating for the particular question this article is asking, which is where human and bat recursive capacities actually diverge in ways the theory cannot already predict.
Nagel asks where a bat seems most alien to a human observer. Living Value Theory asks where the distribution of capacities between bats and humans is least settled. These two questions can point in entirely opposite directions. The sensory system that makes a bat seem extraordinarily alien may belong to a category bats and humans unquestionably share, multisensorial embodiment in a particularly striking form. Meanwhile capacities that look far less exotic on the surface, differentiated relationships between individuals, socially acquired vocal patterns, reciprocal coordination sustained across time, may sit directly on a boundary the theory has not yet resolved.
VI. The Interesting Bat, I: Interrecursivity
Selfrecursivity and nonrecursivity are zoetically secure and were excluded above on exactly that basis. Interrecursivity is different, and the reason is worth stating precisely: being-with does not by itself entail interrecursivity. Two organisms can affect one another, can be mutually present, without either entering the other's recursive organisation in the stronger sense this corpus has developed elsewhere. How much interrecursivity a given species shows, and under what circumstances, therefore remains open across species in a way embodiment or dwelling are not.
The test needs to be defined carefully enough to avoid secretly smuggling in a human standard of mindreading, or the kind of over-attribution a recursive mediational profile can carry when it outruns what a counterpart's own behaviour actually returns as feedback. An interaction is interrecursive when the changing activity of another recursive being enters a focal organism's ongoing recursive field, and the focal organism's response can in turn modify that other being's subsequent activity. This requires reciprocal recursive adjustment between the two. It does not require anything like a linguistic proposition of the form she believes that I believe, and a test that demanded propositional content of this kind would have quietly reintroduced the human-language standard the whole exclusion procedure was designed to avoid.
Bats are an unusually promising case for this question, because many bat species are not merely aggregating animals in the way a colony of nesting seabirds is. Different species show prolonged maternal relationships, stable roosting associations that persist across seasons, individual vocal recognition, differentiated affiliative relationships, conflict, cooperation, grooming, and socially structured vocal behaviour. The empirical question this raises for any given bat, and any given encounter, is precise: is another bat here merely an environmental condition, is it a recognised conspecific category, is it a particular remembered individual, and does its changing activity recursively alter the focal bat's own activity in a reciprocal sequence, or only in a one-way one?
Maternal recognition supplies a first case. Bat pups and their mothers can identify one another acoustically within extremely dense colonies, picking out an individual voice against a background of thousands of simultaneous calls. What kind of recursive organisation this requires is worth asking carefully rather than assuming; it does not license inferring human attachment structures automatically. What can be examined instead is duration, individual differentiation, anticipation of the other's return, behavioural repair following separation, and change produced specifically by reciprocal signalling rather than by proximity alone.
Vampire bats supply a stronger case still. Food sharing among unrelated or distantly related individuals, repeated association across encounters, and relationships that extend beyond immediate kinship are well documented in several populations. The interesting question is not whether vampire bats are friendly in any sense borrowed from human friendship; it is whether repeated reciprocal encounters generate a history that alters later recursive possibilities between two particular individuals specifically, such that a bat that received food from a given partner in the past becomes more likely to share with that same partner later, in a way its behaviour toward an unfamiliar bat does not track. If previous interactions modify expectations and future responses toward one particular counterpart, this is strong evidence for sustained interrecursivity rather than for repeated but independent instances of a fixed rule.
Individually distinctive calls and socially learned vocal features matter for a related reason. Recognition allows an absent history to become relevant within a present encounter: a call can reorganise a bat's present activity precisely because of previous encounters with the specific individual producing it, which moves the coordination beyond simple, simultaneous responsiveness to a shared present.
A likely and theoretically important result follows from all of this. Bats may show rich and sustained interrecursivity without anything resembling human institutional organisation, no shared symbolic classifications, no stabilised roles, no L4 architecture of any kind. If borne out, this would separate two capacities that discussions of social complexity tend to bundle together as though they necessarily travelled as a pair. Interrecursivity, on this evidence, need not imply L4 at all.
Throughout, the evidential status of any particular claim should be kept distinct. Some differentiated reciprocal behaviours are already well demonstrated. Whether they should be interpreted as interrecursive rather than merely associative is, in some cases, still a matter of interpretation rather than settled fact. Whether any bat relationship acquires a form approaching higher recursive stabilisation remains open. The purpose of the comparison is not to promote bats up a ladder relative to other animals; it is to map an uncertain boundary as precisely as the current evidence allows.
VII. The Interesting Bat, II: Communication, Learning, and the Threshold of Multisymbolization
Bats obviously communicate, and the existence of signalling by itself settles very little. Signalling of some kind is present across almost the entire animal kingdom, and its mere presence was never in question. The relevant question is narrower: what kinds of recursive operations does bat communication actually support, once signalling as such is set aside as already expected.
Bat vocal repertoires are, in a number of species, unusually rich: species-specific repertoires, individually distinctive signatures, mother-pup calls, courtship vocalisations, territorial calls, and vocal development shaped by social exposure rather than fixed from birth. Some of these systems are elaborate enough that describing them merely as reflexive signals becomes implausible on its own terms. But complexity of this kind is not itself multisymbolization in the strong sense developed elsewhere in this corpus, and treating complexity and multisymbolization as the same thing would smuggle back in exactly the anthropocentric conflation this article has been trying to dissolve.
Comparative research on animal communication often asks whether a given system shows syntax, semantics, reference, or compositionality, borrowed directly from the analysis of human language. These questions can be legitimate on their own terms. But they also reveal a familiar pattern of relevance selection: animal communication becomes interesting to the extent that it resembles components of human language specifically, rather than being assessed against a standard derived independently of the human case. The question asked here is different in kind. What does a given signalling system allow a recursive being to do with its own prior communicative products, rather than how closely does it resemble a sentence?
A stronger test for multisymbolization can be built from several discriminating probes rather than a single checklist modelled on human language, and no single probe needs to be satisfied for every candidate case. Does a sign operate beyond the immediate situation that elicited it? Does it stably refer to an entity or event that is currently absent? Can existing signs be recombined to produce a meaning neither component carried alone? Can a sign become the object of a further sign operation, a classification of a classification, rather than remaining a first-order response to the world? Is a symbolically organised distinction transmitted from one individual to another rather than independently rediscovered each time? Does a symbolic product persist in a form durable or reproducible enough to be recursively re-entered later, by the same individual or a different one? A signalling system that satisfies several of these probes is a substantially stronger candidate for multisymbolization than one that satisfies none, and the probes are meant to discriminate cases from one another rather than to license a single verdict on animal communication as a whole.
Vocal learning makes bats an especially interesting intermediate case for exactly this reason. Vocal learning, in which a form is socially acquired rather than genetically fixed, occurs in several bat lineages, itself uncommon among mammals. This introduces a form of historical dependence into bat signalling: an individual's present call may bear the trace of previous social interactions rather than expressing an innate template alone. The open question is whether socially transmitted vocal form amounts to nothing more than learned signalling, a highly flexible instance of L1 and L2 coordination, or whether it begins to support a recursively manipulable symbolic organisation in the sense the probes above are meant to test for.
This is a question this article deliberately does not resolve in either direction. Calling bat vocal learning language would overstate the case in exactly the way this article has been arguing against throughout. Declaring it mere signalling would understate it just as badly, foreclosing an open question by definitional fiat rather than by evidence. The whole value of relevant comparison lies in locating uncertain distributions precisely, without forcing them into an inherited binary designed for a different comparison altogether.
Bats improve the overall test in a further respect worth making explicit. Octopuses show striking interrecursivity and multimateriality alongside comparatively weak evidence for anything resembling cumulative vocal tradition. Bats potentially offer a different combination again: strong sociality, vocal learning, and intergenerational transmission of vocal form, alongside relatively constrained manipulation of physical objects. Different species therefore dissociate capacities that human-centred theories tend to bundle together as a single package, social complexity, tool use, and language treated as though they necessarily arrive as a set. Dissociation of exactly this kind is what a comparative theory worth having should want from its evidence, since a theory tested only against cases where its expected clusters hold together intact is never given the chance to be wrong.
VIII. The Interesting Bat, III: Multimateriality, Higher Recursive Levels, and Accumulation
Bats manipulate their environment and interact with physical objects, but their bodily organisation, wings rather than grasping hands, makes detached-object manipulation far less prominent in bat life than it is in primates, corvids, or octopuses. This limitation is itself theoretically informative rather than merely a gap in the evidence. It shows directly that sophisticated cognition does not require anything resembling a human hand.
Human observers are unusually impressed by dexterous object manipulation partly because human evolutionary history made hands extraordinarily consequential for the human lineage specifically, and tool use has correspondingly acquired a disproportionate status as a marker of intelligence in comparative research, a pattern the tool-use and nest-construction study discussed above already demonstrates empirically. A bat destabilises this assumption directly: an organism can apparently possess complex navigation, extensive memory, elaborate communication, and structured social relationships while showing comparatively limited tool-centred poiesis, which suggests these capacities do not travel together as tightly as a hand-centred theory of intelligence would predict.
The evidential burden for attributing anything beyond L2 to a bat should remain correspondingly high. Behavioural persistence does not by itself establish L3. Problem-solving does not establish it. Vocal complexity does not establish it. Social learning does not establish it. What L3 specifically requires is the kind of articulation through which a disturbance or a relation becomes available in a symbolically organised form, available to be held, worked on, and later re-entered, rather than only registered and responded to in the moment. Nothing weaker than this should be allowed to count.
L4 and L5 sharpen the predicted contrast further still. No current evidence establishes anything resembling institutional stabilisation among bats, a symbolic classification maintained across a population and treated as authoritative, or anything resembling the meta-repositioning toward an already-established symbolic framework that L5 names. This is an empirical and conceptual conclusion reached by applying a stated evidential standard, not a definition of bats as deficient approximations of humans, and the distinction matters: the claim is about what current evidence shows, not about what bats are permanently barred from showing.
Accumulation raises a further, distinct question. What survives an individual bat once it dies? Its genes survive. The environment it modified, a roost structure, a foraging route worn into use, survives in some diminished form. Learned vocal forms may survive through social transmission to other individuals who were exposed to them. But a further and more demanding question remains open beyond any of this: does a recursive achievement made by one bat become available to other, absent bats as an achievement they can themselves take up, modify, and pass on again, rather than merely persisting as an unmodified trace? This is the decisive question for accumulation in the strong sense this theory needs, and it should be used cautiously. The issue is not whether bats possess culture under some single stipulated definition borrowed from elsewhere. The more precise question is whether a recursive achievement becomes a starting condition for a further recursive achievement made by someone else, which allows for degrees and partial cases rather than a single verdict, and which creates a direct bridge back to the octopus and dog comparisons developed in the companion piece on the non-human test.
IX. From "What Is It Like?" to "Where Is the Open Boundary?"
The comparison can now be reassembled with the discarded and the surviving dimensions clearly separated. Multisensorial embodiment, being-with, multiversal dwelling, L1, L2, selfrecursivity, and nonrecursivity are all theoretically expected, and their presence in bats, however extraordinary its particular implementation, establishes profound commonality between bats and humans without locating any uncertain frontier between them. Interrecursivity, by contrast, remains open in degree, duration, and organisation. Multimateriality is variable across bat species and comparatively revealing precisely because of that variability. Multisymbolization remains uncertain and demands careful, probe-by-probe criteria rather than a single verdict. L3 and above remain of uncertain distribution. Cumulative recursive transmission remains uncertain. These five, not the seven excluded above, constitute the proper comparative field.
The purpose of this exercise is not to score bats against humans on a single scale, and there need be no single ordering running from less advanced to more advanced across the cases this article has considered. A species can show sophisticated interrecursivity while showing limited multimateriality. Another can display remarkable multimateriality while showing only episodic social interaction. A third may show socially transmitted signalling without strong symbolic recombination of the kind the probes in the previous section were designed to detect. Comparative analysis conducted this way should reveal dissociations of exactly this kind rather than a ranking, because a ranking presupposes the single scale this article has been arguing against from the start.
Dissociation matters for a further, theoretically consequential reason. If capacities Living Value Theory currently expects to cluster together turn out, on careful species-by-species examination, to separate instead, the theory owes an explanation for why they cluster as often as they do in the human case specifically, and an explanation for why they come apart elsewhere. Cross-species comparison, conducted on uncertain dimensions, therefore becomes capable of revising the theory rather than merely illustrating it. A theory tested only against phenomena it already entails can never be seriously challenged by the results, however much confirming evidence accumulates, and that is precisely why the exclusion procedure developed above matters methodologically and not only rhetorically.
X. Toward a General Method of Relevant Species Comparison
The procedure this article has applied to bats generalises directly. Begin with a theoretical question rather than with a species. Identify the full conceptual field that could plausibly bear on that question. Remove whatever characteristics the theory's own architecture already predicts the distribution of, since their presence or absence cannot discriminate anything the theory has not already settled. Remove, separately, any purely analytical category that could not meaningfully vary across organisms in the first place. What remains is the set of capacities whose distribution is open, and it is against this narrowed set, not the original unbounded field, that empirical indicators should be specified, deliberately without defining those indicators around human performance as the implicit standard. The resulting comparison should relate configurations of capacities to one another rather than ranking whole organisms along a single dimension, and it should be built to allow negative and surprising results to revise the theory rather than being quietly absorbed by it.
Living Value Theory's own developed concepts, on the order of a hundred at present, supply one test bed for this procedure at scale, and a natural next project would classify them systematically by comparative status rather than treating this article's handling of a handful of them as exhaustive. Some will turn out to be zoetically entailed, expected wherever life exists at all. Some will be purely analytical, describing the theory's own architecture rather than a variable process. Some will be derivative of other, more basic capacities already classified. What remains after this sorting, likely a considerably smaller set than the whole corpus, constitutes the theory's genuine comparative frontier, and the precise number reached by this sorting is not the point; the principle of selection that generates it is.
Different organisms function as different stress tests for this frontier, each dissociating a different combination of capacities that happen to travel together in the human case. Octopuses test distributed embodiment, multimaterial manipulation, and episodic interrecursivity. Bats test rich social and vocal coordination in an organism with a radically unfamiliar sensory architecture and comparatively constrained manipulative materiality. Corvids would generate a further profile again, and great apes another, and social insects another still; plants and fungi push the frontier further outward, into territory where even some of the currently excluded dimensions become worth reopening. The aim throughout is never to find the organism closest to a human being. It is to find organisms that dissociate dimensions humans happen to combine, since it is exactly that combination, not any one capacity considered alone, that makes the human case comparatively distinctive.
This licenses a final reformulation of the question comparative work should be asking. Not how human is this animal, a question that already presupposes the human case as the standard against which every other species is measured. Instead: which theoretically uncertain forms of recursive organisation occur here, and to what degree. The second question is both less anthropocentric than the first and considerably more demanding of the evidence, and it is the question this article has been asking of bats throughout.
XI. Why This Matters for Philosophical Anthropology
The long history of proposed anthropological differences, reason, language, tools, morality, culture, self-consciousness, awareness of mortality, institutions, need not be treated as a history of mistakes. Each of these proposals may identify something real and important about human life. The error has never been in the proposals themselves so much as in treating their importance as self-evident, exempt from the same justification any other comparative claim would need to supply.
A theory of comparative relevance does not abolish anthropological difference, and nothing here has been aimed at that broader project. What it does is make claims about anthropological difference answerable to an explicit criterion of selection, rather than allowing a criterion to operate silently behind an argument that presents itself as simply describing what is there to be found. This also changes philosophical anthropology's relation to biology in a specific way. Animals stop functioning merely as boundary tests for capacities humans already prize in themselves, waiting to be found wanting or, occasionally, surprisingly capable. Different organisms become experimental challenges to the assumption that certain capacities necessarily travel together at all, since it is exactly that assumption, more than any single capacity taken alone, that a comparative theory has reason to doubt. On this view the human being becomes one recursive configuration among others, albeit one with extraordinary poietic elaborations this article has not sought to minimise anywhere along the way.
XII. Conclusion: What Is Relevant About Being a Bat?
Return, one last time, to Nagel. His question remains profound: what is it like to be a bat? But its profundity belongs to a particular philosophical problem, the problem of subjective experience and its resistance to objective reduction, and it should not be asked to determine the general architecture of human-animal comparison beyond that problem. Echolocation is precisely the kind of difference a theory of multisensorially embodied life should expect to find somewhere in the animal kingdom. It is extraordinary in its implementation and unsurprising in its theoretical category.
The more revealing bat lies elsewhere: in differentiated relationships sustained across time, in reciprocal social histories that alter later behaviour toward specific individuals, in vocal learning and socially transmitted form, in an uncertain boundary between mere communication and something stronger. Reversed one final time: Nagel asked where the bat is most phenomenally inaccessible to a human being. Relevant comparison asks where the boundary between bat and human capacities remains unknown. The first question reveals the limits of imagining another creature's subjectivity from the inside. The second reveals the limits of our own theories, a different and, for a comparative theory, a more useful thing to have exposed.
There are indefinitely many ways in which a human being differs from a bat. The scientifically and philosophically difficult task was never finding differences; a list of them could be extended without end. The difficult task is earning the right to call any particular difference relevant.