The (process) metaphysics of evolution


Heraclitus, by Hendrick ter Brugghen

Metaphysics isn’t exactly the first thing that comes to mind when someone is thinking about the theory of evolution, especially if that someone is an evolutionary biologist who is reasonably skeptical of any metaphysical claim — like yours truly.

Nonetheless, my Exeter University colleague John Dupré has published a stimulating paper that seeks to apply so-called process metaphysics to modern debates in evolutionary biology (full paper here). The result is intriguing, though that doesn’t mean I’m completely on board with what John writes.

Let’s start with the basics. Dupré defines metaphysics as the branch of philosophy that aspires to provide the most general description of reality. You would think that nowadays that aspiration falls squarely within fundamental physics, except for the fact that fundamental physics — as interesting as it is — is largely irrelevant to most of the other sciences, and “the most general description of reality” can’t be just the description of whatever is at the bottom of reality.

John also argues, and I think he is completely right about it, that:

“Though they may sincerely deny it, scientists are almost inevitably committed to metaphysical opinions. … Metaphysics can be ignored but not escaped.”

If that’s true, then we (philosophers) better get our metaphysics straight, and we (biologist) better pay attention to the consequences of our own assumptions on the matter, regardless of whether these assumptions are explicitly stated or not (in fact, particularly if they are not explicitly stated).

The way Dupré goes about this is by applying some philosophical reflection to the scientific work done by biologists, to see if certain metaphysical commitments made by scientists don’t turn out to be incorrect in the light of the scientists’ own work. Specifically, in this paper he explores a very old question in metaphysics: whether the world is composed of things or processes. The first position goes back at least to the Ancient Greek atomists, like Leucippus and Democritus (or, in India, the Jain, Ajivika and Carvaka schools, possibly dating back to the 4th century BCE). The second position was espoused by Heraclitus, and made famous by the Latin version of his dictum, panta rhei, “everything flows.” Nowadays, they are known in philosophy respectively as substance and process metaphysics.

Substance metaphysics implies an ontology of things (as opposed to an ontology of processes), and it has been dominant since the beginning of the scientific revolution in the 17th century. It is connected to the mechanicist approach, where everything is made of things with particular functions, and those things constitute the mechanisms that explain how the world works. Mechanicism in turn implies reductionism: things are made more and more complex from the bottom up, and the causal story is unidirectional.

Contrast this with the more fluid (ah!) process ontology, which rejects both mechanicism and reductionism: what maintains patterns of stability in the world isn’t just the behavior of individual entities, but also the network of relations among patterns and between patterns and the environment in which they are situated. I must confess that I started out, decades ago, as a mechanicist who believed in an ontology of things, just like most scientists do (especially physicists). But it was my own scientific research in evolutionary biology (particularly writing this book) that gradually interested me more and more in an ontology of processes and a less reductionist view of things. Only I didn’t know (until I turned professionally to philosophy) that this was called process ontology, and that it was a well worked out position among metaphysicians.

In his essay, Dupré applies this debate to the nature of biological species (see this paper of mine) and to our conception of evolutionary processes in general. As he clarifies, of course substance ontologists recognize that evolution is a process, but they think it is made possible by the more fundamental existence of things. For process ontologists, by contrast, everything — including living organisms — is a process. There is nothing stable. Panta rhei.

John explains very nicely the contrast between substance and process ontology. Consider the difference between a mountain and a storm. For a substance ontologist, the first one is a stable object, the second a process. But the process ontologist sees both as processes, only at very different time scales: the mountain changes continuously, but it takes millions of years for the change to be noticeable by the human eye. The storm also changes, obviously, but much more rapidly.

Then again, some storms are remarkably persistent, though in a dynamic fashion. Think of the famous Red Spot on Jupiter, which has been observed now for hundreds of years. Process ontologists think that a dynamic storm is a better paradigm for living organisms than a mountain. After all, when living beings achieve a stationary state we call them dead. As my professor of biophysics back in college, Mario Ageno (a student of Fermi, article in Italian), used to say: death is a sudden increase in entropy.

Why does it matter to think of organisms as processes rather than things? Dupré Suggests two reasons:

“The first is that it motivates a significant shift in emphasis with respect to what stands in need of explanation. The traditional concern for thing-centred ontology is change. I do not expect an explanation of why my desk is very much as I left it when I was last in my office. For a process, on the other hand, persistence requires explanation. Physiology is largely concerned with understanding the multitude of internal processes that enable an organism to stay alive, to maintain its thermodynamic disequilibrium with its environment. … The second reason why the processual status of organisms is important is that it places in the proper perspective the search for mechanistic explanation that is often alleged to be central to the contemporary life sciences. I take a mechanistic explanation to be, very roughly, one that involves identifying a set of constituents of a phenomenon and showing how their actions and interactions combine to generate the phenomenon. There is no doubt that this has been an enormously productive scientific strategy. Nonetheless, from a process perspective the mechanisms postulated by such explanations must always be abstractions from the wider biological context, and this always poses potential limits on their application.”

As a result, the organism should be seen not as a set of interlocking things (cells, sub-cellular components, individual molecules), but as a hierarchy of processes acting at different levels (molecular, physiological, and so forth).

If all of this sounds a bit abstract, that’s okay, it’s metaphysics, after all. To make things more concrete, John goes through a fairly in-depth analysis of the question of what evolves, i.e., what is the unit of evolution, in the process making some important clarifications on the nature of biological species.

It is an accepted truism in biology that individuals do not evolve, populations do. Then again, what counts as an individual? This is a very broad, and controversial question, but let’s focus on just one aspect of it: are species themselves “kinds” or individuals? Most biologists, I’m guessing, would answer that of course species are kinds, meaning categories to which a number of individual things belong, if these things satisfy certain criteria. For instance, Homo sapiens is a kind, to which all organisms that are statistically characterized by a certain type of genome, certain physiological, anatomical, developmental, and even cultural attributes, belong. Pan troglodites, a species of chimpanzee, is an evolutionarily related kind, to which all organisms satisfying certain other characteristics belong. And so forth.

However, most philosophers of biology accept some classical arguments put forth by Michael Ghiselin and David Hull, according to which species are not kinds, but rather individuals. If one accepts modern cladistic systematics, species are individuals identified by branches on a phylogenetic tree. This possibility was actually first brought up by a paleontologist, Steven Stanley, in a paper entitled “A theory of evolution above the species level” (pdf here).

Dupré accepts Ghiselin and Hull’s account, with some provisos inspired by his endorsement of process ontology. The most important of these provisos is that a branch of a phylogenetic tree is, of course, a process, not a thing. This neatly resolves a long standing problem for the species-as-individuals view: species change over time, but we said above that individuals do not evolve, populations do, so what gives? The answer is that species are individuals in the same sense that organisms are, even though organisms develop and change in the course of their short lifetime, while species change over longer evolutionary times. In both cases, we are talking about dynamic processes, not static things. That also explains why species typically have fuzzy boundaries: do you expect a thunderstorm to have a sharp and neat boundary, an exact point beyond which it is no longer a storm?

It is important to note, as John does in his paper, that not all processes generate individuals. Geological erosion is a process, but it doesn’t turn up anything like biological species. In order to do that, one needs a stabilizing process. In biology a major, though not the only, stabilizing process is natural selection, which tends to keep variants that are (locally, both spatially and temporally) sufficiently suited to the environment.

One consequence of this view of species as organisms that result from the stabilization of processes is that for most of the evolution of life on Earth there were no such thing as species-as-individuals. Bacteria are not stabilized in the required fashion, because their lineages do not actually identify species at all. And they don’t because they lack sexual reproduction, another major source of stabilization in multicellular species. John sees, correctly I think, the emergence of sex as making possible the emergence of species as individuals.

There is a lot more in the paper, where the author touches on a panoply of fascinating ideas in modern biology, from niche construction to epigenetic inheritance, from parental care to the evolution of culture. John’s treatment of the subject has wide ranging consequences, as he summarizes near the end of the paper:

“If species are what evolve, we should not, for this reason, expect quite general accounts of evolution. The Modern Synthesis [i.e., the increasingly less dominant standard model in biology], specifically, may be more or less true for some kinds of species, but quite inadequate for others. If species have evolved new forms of evolvability [because of the invention of sex], this is surely to be expected. Evolvability of many populations may just be a summative property of organism properties, but as species become integrated processes it is plausible that evolvability might emerge as a specific capacity of lineages.”

Evolutionary mechanisms themselves, in other words, evolve. And they do so because everything in biology is a process, not a thing.

107 thoughts on “The (process) metaphysics of evolution

  1. Massimo Post author


    Most scientists think of themselves as being in the business of figuring out how the world really works. Of course, for that they do need to rely on certain metaphysical assumptions.

    And no, metaphysicians are definitely not gods. Some of them much less so than others…

    Liked by 1 person

  2. Douglass Smith

    Thanks for your continued discussion on this topic, Massimo. I have to admit I can’t yet get my mind around the claim that there can exist relations without relata, except perhaps in the theoretical sense that we can discuss one without the other. That said, I haven’t read Ladyman.

    As for the word “thing”, it seems as though you consider it a theoretically thick descriptive term, whereas I consider it a thin term of ordinary language. It seems to me to be pretty much an empty designator; we call nihilists folks who claim “nothing exists”. Of course you are not a nihilist!

    As a term of ordinary language, very stable objects are things (Side question: is there any difference between the word “object” and the word “thing” in this context? If not, then don’t things exist in some sense?), but then so are structures, descriptions, etc.

    The theoretically thick descriptive terms would be ones like “substance”, etc.; terms of art with well-worked-out definitions. We can well say that there are no substances.

    My concern with the claim “There are no things” is that it is rather like the claim “There are no selves” that some make in Buddhism; that is, it threatens to become a Motte and Bailey doctrine. Sure, there are things and selves, but they are basically incompletely identified constructs of a kind. There are no substances, there are no souls. Does this make sense?


  3. Philip Thrift

    I tend to reject both pure process ontology and that there are separate process and thing/substance, but tend toward a “processual substance” ontology. But I’m not aware of this being expressed outside postmodern philosophy.

    Liked by 1 person

  4. SocraticGadfly

    Massimo, per Dan, does something like this and your degree of acceptance of it make you less of a species realist?

    Related philosophical question — how do philosophers in general deal with the idea of processes vs. things?

    Plato himself talked about the reality, or Reality, of Nouns and also Adjectives, but not that of verbs or even gerunds. There was no ultimate Walking, Talking or Quacking, even if there was an ultimate Duck.

    Of course, as I’m sure Massimo has seen, our friend Diogenes took care of that long ago:

    Liked by 1 person

  5. Philosopher Eric

    Most scientists think of themselves as being in the business of figuring out how the world really works.

    But that seems like the exact sort of mistaken belief that philosophers should try to relieve them of rather than repeat…


  6. Massimo Post author


    Ladyman & Ross’s book is a tough nut to crack, but yes, they do argue for the ultimate existence of only relations, no relata, and therefore no things understood as particles, strings, and so forth. At bottom there are only fields, which are dynamic processes

    Substance ontology uses the word “substance” in the thick sense, it’s a technical term. And there are plenty of substance ontologists around, though my understanding is the process metaphysics is on the rise (I’m not a metaphysician, so my pulse of the field is only indirect).

    Again, I think your difficulty comes from the fact that you have long ago inherently accepted a type of process metaphysics, but not everyone has been, or even is right now, on board with that.


    As I explained earlier, any mixed system is by definition a type of substance ontology. There is no such thing as “impure” process ontology.


    I am a realist about species in the sense that — contra Darwin — I don’t think that species boundaries are arbitrarily drawn by humans for purposes of classification. Darwin thought so because he was married to an extreme version of gradualism in evolution. I’m not. But I am what people may describe a type of pluralist about species: I don’t think that a “species” of bacteria is the same kind of “thing” (so to speak!) as a species of plants, or of mammals.

    I’m not sure how philosophers in general deal with processes vs things. I guess for most the question is irrelevant, as they don’t deal with situations where it arises (e.g., ethics, aesthetics, philosophy of law, etc.).

    Liked by 1 person

  7. Daniel Kaufman

    Massimo: Please say so if you don’t want the conversation going down this particular road, but could you briefly explain how species classification — or any classification — could be anything but linguistic and therefore, conventional? Seems to me that one runs into the “gavagai” problem immediately, which shows that any specific classification, beyond an indefinite disjunction of extensionally equivalent ones, has to be inherently intensional (with an ‘s’) and thus, not a part of nature, but rather of the language we use to to talk about it.

    Might be a good topic for our next dialogue, no?

    Liked by 1 person

  8. Daniel Kaufman

    Addendum: Indeed, Quine was so worried about this problem that he wanted to exclude the intensional idiom from science. Of course, if one did that, one could never get the highly specific, fine-grained classifications that one routinely finds in science. It would look very different.


  9. brodix

    Wouldn’t that be an ideal duck, not an ultimate duck?
    As a perfect form, an ideal would seem to be a stable state, like mathematical platonism, while an ultimate duck would be more of a duck singularity.
    A goal towards which duckism is drawn. As such, still implicitly process.


  10. synred

    david D: If by ‘motor’ they mean motor, I don’t see how information can power it. Storing information creates entropy (hence it’s one way nature). It seems memory storage would use free energy.


  11. synred

    we call nihilists folks who claim “nothing exists”.

    I thought nihilist thought nothing mattered. Nothing exist is self-contradictory as at least the mindless process saying ‘nothing exist’ exist.

    Liked by 2 people

  12. SocraticGadfly

    Thanks on the explainer on biology, Massimo. On philosophy, though, on things like aesthetics and ethics, aren’t there still some Platonic True Good Beautiful devotees? I would mention some Christians, but then we’d get into what was a non-trivial argument, contra pin-headed angels, between nominalists and realists.

    Speaking of, isn’t Plato kind of hoist by his own Euthyphro petard? Hmmmmm


  13. synred

    Ladyman & Ross’s book is a tough nut to crack, but yes, they do argue for the ultimate existence of only relations, no relata, and therefore no things understood as particles, strings, and so forth. At bottom there are only fields, which are dynamic processes

    I don’t see why fields can not be called ‘things’. It true there’s a lot of virtual particles associated with fields, but while there’s a lot of loose process like talk about virtual particles popping in and out of existence, it’s not really process. All that is ‘popping’ is diagrams being added to make a calculation.

    A string of Feynman diagrams being added is not a time sequence. It doesn’t matter what order you add them in for the result (though they are usually added in the order of complexity because it takes longer to do the calculation as the more stuff ‘pops’ in a diagram).

    There is a time variable in the diagrams but it’s still just calculation. An excitation of the electron field (an electron) is arguably a process, but it is an excitation of the field which in the absence of excitations just sits.

    It seems to me the whole business is some linguistic confusion where the underlying stuff/activity is just not describable in our available language. You’re pretty much stuck with the math for describing it (might help if we actually knew the correct math).

    Well that was a waste I guess. I think I’ve fallen out of the comment window out her in calif.


  14. brodix

    It seems to me that one driver of form is the limit to which the motivating energy can expand and fill out the given space/niche, relative to how this context pushes back.
    Nature out, nurture in.
    As such, it would be meaningless to consider the ideal as an essential feature of the object, since it shape is as much a function of context.
    The node is as much a product of the network, as the network is a relationship of the nodes.


  15. SocraticGadfly

    Per Dan, Wikipedia’s page on the matter separates underdetermination of scientific theory from the two linguistic angles of Quine’s

    In that third category, referred to as “confirmation holism” at the clicked line, I don’t think intension comes into play the same way. The Wiki piece refers to the web-of-belief idea being a key issue, which certainly sounds like it on the issue at hand.

    That said, it does sound like an issue for further exploration from this angle.


  16. SocraticGadfly

    Just in case comments with multiple links “hang up,” writing separately, it’s interesting that Linnean taxonomy is a specific reference in Wiki’s piece on intensional definition.

    I would think that to the degree definition of the word “species” is a problem, one simply works on a better definition. Maybe it has to be “looser.” Or maybe “genus” above it has to be adjusted as well.


  17. Daniel Kaufman

    This has nothing to do with web of belief. The point is the following:

    = The claim is that species classifications are real, not the result of linguistic convention.

    = Thus, nature really contains rodents. But nature does not really contain Rodent-stages.

    = However, Rodents and Rodent stages are extensionally equivalent. They only differ intensionally.

    = Nature cannot make distinctions between intensionally different versions of extensionally equivalent things or classes. Intensionally different versions of extensionally different things are a matter of differences in mode of presentation (i.e. representation), which is only discernible to minds.

    = Species classifications as specific as Rodents are therefore intensional and linguistic and therefore, conventional.

    **Again, as I said earlier, Quine thought intensional language unsuitable for science, precisely for this kind of reason, which is why he eschews synonymy and modality, in favor of a purely extensional language for science. I think he is right — i.e. that the language of science must be purely extensional — but that means that any distinctions or classifications more fine-grained than extensional ones must be linguistic and thus, matters of convention.


  18. Massimo Post author

    Sorry Dan but I have to wholly disagree. I’m not even sure the argument makes sense, pace Quine. Rodents exist. They are are a discernible species in nature. That means they are different, in qualitative and quantitative ways, from any other group of animals.

    The fact that humans use certain language to describe all this is certainly a human convention. But there is little doubt, in this case, that the language reflects reality out there. Do you think there are stars? Planets? Galaxies? Electrons? Etc. All of these, obviously, are human terms and concepts. But some of these concepts do pick out stuff that is out there, and would be independently of human thought. So I’m really not sure what the problem is, Quine or no Quine.

    Liked by 2 people

  19. Massimo Post author


    There may be some devotees of Plato and his theory of forms out there. Usually they are mathematicians. You know what I think of that.


  20. Daniel Kaufman

    Massimo: That’s a different problem, one that is better directed towards the sorts of arguments Nelson Goodman makes in Ways of Worldmaking. This is purely a problem about how fine-grained the categories that we attribute to really belonging to nature can be. My point just is that I don’t see how you can ascribe any classification as really belonging to nature, beyond that which is individuated extensionally.

    Why do you think Quine believed that intensional notions couldn’t be part of the language of science?


  21. Daniel Kaufman

    Last thing, and then I’ll drop it. The whole thing is just a brainstorm anyway.

    My idea was this. The classic anti-realist point is that the idea that the world comes pre-cut at the joints doesn’t seem credible. This then puts you into a dialectic that full-blown anti-realists, Kantian noumenalists, and others.

    But another question you could ask is this: “Ok, say we accept that the world comes pre-cut at the joints. How detailed/fine-grained is that pre-cut? My thought was that you could use Quine to argue that it can only come pre-cut to a certain degree; that the rest is done by human conceptual schemes and thus, language.


  22. synred

    There were always ‘spilters’ and ‘joiners’ in classification. There always be even in the age of DNA.

    There are real groupings out there, some looser (polar bears vs. grizzlies) some tighter (cats vs. dogs). Exactly how we name them and mark them off is in the human/linguistic’ domain.

    Fuzziness is always with us.

    Liked by 1 person

  23. Massimo Post author


    I don’t think this has much to do with neat cuts at the joints of nature. Again, I ask: do you (or Quine) think that there are planets out there? As Synred says, the fact that there are fuzzy boundaries is irrelevant, there is still a pretty clear distinction, overall, between planets and stars. And so there is between rodents and non-rodents. How fine these distinctions can reasonably be made is an empirical question.

    I’m not even sure what’s “intensional” here about the language of biologists about species. I know we are not arguing about terminology, which is of course arbitrary. Biologists have determined that phylogenetic branches are the natural results of the evolutionary process. Would Quine object to that notion? What would he say instead? I’m truly curious.

    Liked by 1 person

  24. Daniel Kaufman

    Again, I’ve just been brainstorming, so everything I’ve said is by necessity half-baked.

    My inclination with regard to kind-classifications of every kind are qualified anti-realist. (Sort of like Hume on skepticism, I’m an anti-realist when I’m in the seminar room and a naive realist, when I am out on the street.) It just seems to me that our classifications are too dependent on the particularities of our particular sensory apparatus and language for it to be anything other than a cosmic accident that it should turn out that as a matter of fact, the world just happens to be carved up that way. I could imagine beings who don’t perceive reality in terms of discrete objects in space — and such creatures would not develop a classification system that depended on differentiating characteristics that consisted of things like organs or circulatory systems or vertebrae or the like.

    So that’s one problem — call it the classic Goodman problem. But then I was wondering whether there is another, less severe problem. One that allows for realism about classifications, but only one in which the real classifications consist only of those kinds that can be individuated in purely extensional terms. And that was where the Quine came in.

    I don’t know enough about actual biological classifications to know if this example is a good one or not, but take the following made-up case. Assume that all creatures with hearts are creatures with kidneys and vice versa, such that ‘creature with a heart’ and ‘creature with a kidney’ or extensionally equivalent. Now suppose that our zoological taxonomy made a further distinction, individuating K-creatures and H-creatures. Such a classification couldn’t be “real,” because its not a distinction that could exist in the world other than as it is described by human language for the reasons Quine indicates.

    That was the idea anyway. Whether it works as an argument for the conventional nature of at last some biological classifications, like species or some other, is beyond my very meager biology knowledge .


  25. SocraticGadfly

    I should have put a question in my last comment before this one — Massimo, do YOU think “species” (or other taxonomic terms) need redefinition, whether for flexibility of the type you envision or other reasons?


    I’m not a professional biologist, of course, but I am a semi-avid birder. And, I know that, in the last 20 years, largely due to DNA issues, we’ve seen two subspecies of, say, grouse, elevated into separate species, or, in other cases, two species of some other type of bird demoted into subspecies. In some cases, this is after a movement the other direction no more than 50 or so years ago.


  26. SocraticGadfly

    Thanks for Massimo’s other comments back. Unless “the demarcation problem” is considered part of philosophical intention, I couldn’t see how it was involved. I threw out web-of-belief as mentioned in the underdetermination of science not because it made a lot of sense, but because it made more sense than that.

    And, your last sentence ties in with my comment about species and subspecies.


    And, speaking of birding, and environmentalism in general, this is not just a philosophical question. In the US, it’s a legal one.

    Subspecies are in general not eligible for Endangered Species Act consideration. Species, of course, are.


  27. Alan White

    If I made intrude into the debate about meaning and reference between Massimo and Dan, there are points to be made in both directions, but overall I wish to argue briefly in favor of Massimo’s position, at least with respect to some “stable-reference” (as I will call it) terms in biology.

    First, we know that some terms, like “race”, are unstable in reference. Why? The fact that the use of “race” might seem to genuinely refer to real contrasts in skin-tone–a supposed empirical content for the use of the term–is insufficient to support its use in general, especially to describe particular individuals, particularly ones who have intermediate skin-tone (according to the usual uses of “race”).. Furthermore, there turns out to be no other good empirical referent (genetic variation and so on) to support a stable use of the term.

    But then there are terms that do have sufficient empirical content to stabilize their continued use, including terms like “gene” , “species”, and even “evolution”, and despite some remaining vagueness about some uses of the terms in some contexts.

    So, I’d argue that what stabilizes scientific terms in general is sufficient empirical content, and this judgment of sufficiency is made by the collective group of scientists who use (or discard) the terms. All this is compatible with the meaning of terms changing (or being discarded) along with changing standards of reference. FWIW.


  28. Massimo Post author


    Again, I’m engaging here out of genuine curiosity. (I always do, or try to anyway!) I think we should distinguish between classification and natural kinds. Classification can be done for entirely utilitarian (not in the ethical sense!) reasons, practical applications, convenience, etc.

    But ever since Darwin biologists have tried to classify living organisms in a way that reflects the reality of nature, particularly evolution.

    You are certainly right that we are limited by our own perception of the world, but then again science doesn’t limit itself to the five standard senses. Much modern biological classification relies on large quantitative data that are analyzed by computers, not humans, and especially on empirical evidence at the molecular level.

    So, no, the bet is that any intelligent creature would arrive at a reconstruction of the tree of life similar to our own, because that reconstruction reflects how things really are in nature, not our specific preconceptions and sensorial limitations.

    Of course that doesn’t mean the current classification is the final one, nor that there aren’t fuzzy boundaries and so forth.

    As for the truly Quinean problem, I must have gotten more dense since I got to Rome the other day, but I don’t get it. Your example of K- and H-creatures does not seem to be a problem at all. Either there is such distinction in nature, in which case the classification is biologically sound, or there aren’t, in which case it is wrong. Help me out.


    As I said, I think there are different kinds of species out there, defined by the marked differences in the evolvability (i.e., the capacity and propensity to evolve) of different lineages. So it is misleading when we talk about a “species” of bacteria as if it were the same sort of “species” that characterizes mammals. There is a family resemblance, but no more than that.

    Also, what Alan said.


    I got through Ladyman’s book with college level physics, but it was hard. I had to constantly look up things, and occasionally ask a colleague who was either a physicist or a philosopher of physics. But it was well worth the effort. I’m not sure I accept their view wholesale, but it certainly has opened up new ways of thinking about the deep structure of the world.


Comments are closed.