Panpsychism hangs around like a bad penny

July 25, 2021 • 12:00 pm

I’ve written a fair bit about panpsychism (see here for all the posts), and I don’t really feel in the mood to summarize the problems at length. Suffice it to say that it’s a “theory”—probably an untestable one, or maybe it’s better seen as a religion—that every bit of matter in the Universe has some form of consciousness, including electrons and rocks, and if you put them together the right way, as in a dog or a human, you get “higher” consciousness automatically. It’s a “turtles all the way down” view that finesses the problem of consciousness—i.e., how we get qualia, or subjective sensations—by simply making up stuff.

The problems with it are many, and you can read my posts to see the issues that I and others have found with it. They include the following:

a.) There’s no evidence that rocks or electrons or water are “conscious”, and there’s no way to find out if they are because the proponents never define what it means for this kind of matter to be conscious.

b.) There’s the “combination problem”: how do we put together “conscious” molecules in a way to create the kind of consciousness that humans have? At what point do “qualia” appear. If you make a complex machine like a typewriter, it’s a combination of lots of conscious molecules, too, but doesn’t have “higher” consciousness. There has been no convincing solution to the “combination problem” by even the advocates of panpsychism

c.) A problem raised by one of its proponents (one of the four boosters whom Salon uses to say panpsychism is “gaining steam”:

“Panpsychists think you can’t explain human consciousness by putting together lots of non-conscious things in the right structure; okay, but is it actually easier to explain it by putting lots of conscious things in the right structure?” Roelofs asked.

c.) The entire theory is untestable, as one of the proponents admits in the Salon article below (click on screenshot). It is not a scientific theory as much as mental masturbation. At least scientific theories of consciousness, like what neurons are required to have it, and how to change or eliminate it, can be testable.

Count on Salon, the Daily MIrror of websites, to have an article claiming that panpsychism is “gaining steam in science communities.” There’s no evidence adduced at all that the theory is spreading in science communities. Author Rozsa cites, beside Philip Goff, one of the theory’s long-time proponents, only three other people who accept this cockamamie view. None of them are scientists; all four are philosophers of mind. Nor is the author of the piece a scientist. That’s because no respectable scientist would say we should study how consciousness arises by simply assuming that all matter is inherently conscious.

Read and weep:

Here’s how the article frames the “hard problem” of consciousness:

On the other hand, science is equally stuck when it comes to explaining the subjective experiences that we can embrace when we listen to music, enjoy delicious food, watch a movie or fall in love. There is something unquantifiable about the joys of life, a reality that is not encompassed when we try to reduce emotions to hormones.

. . .”Consciousness involves quality — the redness of a red experience, the smell of coffee, the taste of mint,” Goff said. “These qualities that can’t be captured in a purely quantitative vocabulary of mathematics. So Galileo said that if we want mathematical science, we need to take consciousness out of the domain of science. In Galileo’s worldview, there is this radical division in nature between the quantitative mathematical domain of science and the physical world, and the qualitative domain of consciousness with its colors, and sounds, and smells and tastes.”

My own view, which I derived from Patricia Churchland, is that consciousness is an epiphenomenon of a certain arrangement of living molecules, most of them in the brain. Once you have all the ingredients for consciousness in place (and science is beginning to learn about some of them), then you get the phenomenon of consciousness and the presence of subjective sensation. End of the story; nothing more to find out. To me, there’s nothing more to the explanation than that: once the components are there, the being is conscious. The scientific task is to find those components and, if we could, assemble them to see if we get consciousness, or at least fiddle with them to see if we can alter, diminish, or erase consciousness in predictable ways.

But I’m not a neuroscientist, so I’ll leave it to people like Churchland to go after panpsychism. The fact is that, contra Salon, the idea is not gaining steam, but winding down as people realize that panpsychism is a worldview that is absolutely untestable. In fact, Luke Roelofs at NYU more or less admits that:

“Panpsychism does suggest that there may well be some level of consciousness everywhere in nature,” Roelofs explained. “Panpsychists all accept dog-consciousness, but some might not want to accept chair-consciousness: they might say that each particle making up the chair is conscious, but it’s not constructed the right way for these to ‘add up’ to anything. Others might think that chairs have consciousness, but of an incredibly diffuse sort: because there’s no brain or nervous system, there’s no order or structure to the chair’s experience, just an undifferentiated blur.”

Ultimately, he added, “The impact of panpsychism isn’t so much to answer these questions, but to suggest continuity: don’t expect to find a discontinuous boundary somewhere between the simplest animal that is conscious and the most complex animal that isn’t.” Roelofs says there isn’t a line that one could draw: “even if some sorts of consciousness are so simple that it’s more useful for us, in practice, to treat them as ‘mindless’, nevertheless the differences are ultimately just matters of degree.”

In the end, it may prove impossible to ever definitively ascertain whether panpsychism holds water.

Well, if it doesn’t answer questions but “suggests continuity” (that is, positing that all matter is conscious), then it cannot form a program for scientific research.

Well, as Sabine Hossenfelder said in the video this morning (see Hili dialogue), if a scientific theory doesn’t help us make progress in understanding the universe, it should be thrown into the bin for the cockatoos to eat. And surely panpsychism is such a theory.

Two more points. In trying to explain why inanimate matter might be conscious, Roelofs produces a classic Deepity (I’ll put it in bold):

“Panpsychists think that thought, reasoning, decision-making, vision and hearing and smell and all of our cognitive complexity: none of those are the same thing as consciousness. Consciousness is just subjectivity, just ‘is there something it’s like to exist right now?’ And so they think it makes sense for consciousness to exist in simple forms without thought, without reasoning, without vision or hearing or smell. A lot of critics think that’s just a mix-up: they think that once you take away thought, reasoning, etc. that’s it, there’s nothing left to talk about.”

I don’t understand what the “subjectivity” of an atom can be: does an atom know “what it’s like to exist right now”? No, “consciousness is just subjectivity” is a Deepity, which sounds good, but when you dig deeper, you find. . . well, empty words.

Finally, the proponents of panpsychism are now pointing out that it may help us live on after death. Many people want that (that’s why there’s Christianity), and if every atom in our brain is conscious, is it beyond possibility that maybe, just maybe, our memories could live on in those molecules? Yes, I know it’s stupid, but here’s what Salon says:

Panpsychism also has radical implications for religions, since so many focus on questions of what happens after we die. It is likely that our brains still comprise the bulk of our identity (so when the neurons which store your memories die, the memories most likely die forever along with them), but panpsychism allows for the possibility that your conscious “self” lives on in some form. It does not even entirely preclude the possibility that we take some of our identity with us; to paraphrase Stanley Kubrick when he directed “The Shining,” the seemingly horrifying prospect of ghosts existing at least means that death is not final.

Fine; let the theologians discuss this, but I reject it since there’s no evidence. The paragraph above is simply porcine shampoo, that is, hogwash.

When the panpsychists start making real progress in understanding consciousness instead of simply positing an infinite regress of the phenomenon, then we can talk.


h/t: Tim

49 thoughts on “Panpsychism hangs around like a bad penny

  1. Haven’t read the post yet as it is late, but here’s a new paper from Sean Carroll stating that there are serious constraints on it from particle physics. (Which is an argument I made in the past elsewhere, but I digress.)

      1. Not sure but you may have misread. Vampyricon wrote that the paper says that there ARE serious constraints from particle physics.

  2. The final quoted paragraph makes me wonder whether the authors are angling for a Templeton grant.

  3. To the extent that different individuals can have the same subjective experience, and their experiences can be ascribed or mapped to neurons in the same part of the brain of each person, that doesn’t seem subjective. So I guess I agree with Churchland.

    “[T]he redness of a red experience” seems like one really obvious example: people who can’t see red have the same subjective or qualitative experience of redness (its absence). I don’t understand how panpsychists can ignore that.

    It seems likely that many qualia will eventually move into that category as neuroscience progresses. Or maybe there is something about the panpsychist stance that I don’t understand (also seems likely).

  4. …”mental masturbation,” “porcine shampoo”…major🔥! Love it!
    But seriously, the reference to Deepity points us to what can be seen as the religious subtext. Panpsychism seems to be the last refuge of New Age thinking wherein the foundational belief is that the material world is alive in its entirety. Panpsychism is thus a pseudoscientific slight of hand for pantheism. Remember that in Deepak Chopra’s teaching, Consciousness=God, or Atman-Brahman, according to his pseudoscientific repackaging of the Vedanta. In this, he follows his guru, Maharishi Mahesh Yogi, who pseudoscientifically repackaged traditional yogic meditation techniques as the Science of Creative Intelligence, in Sanskrit, Atma Vidya. Hinduism for “scientific” Westerners.

  5. Churchland said it well. When not much is known about a domain of phenomena, our inability to imagine a mechanism is a rather uninteresting psychological fact about us, not an interesting metaphysical fact about the world.

  6. “Porcine shampoo” serves as an excellent summary. (I never heard of that term before; I love it.)

  7. I think the case for “pan-free-willism” is much stronger than the case for panpsychism. There is no known property of fundamental particles that corresponds to consciousness. But there is for free will. An electron passing through a Stern-Gerlach magnet seemingly “decides” to spin in one direction or another. There are no antecedent conditions about the electron or its surrounding that determine its “decision.” That is about as close to “free will” as you can get.

      1. But wouldn’t free will, if it exists, look random? If the outcome could be related to existing or pre-existing conditions, we would say it is determined and the question of free will would not arise. Also, a free will decision is contained to the deciding entity, which it is in the case of the electron.

  8. My computer keyboard wonders: if the molecules that make up my brain, and their physical arrangement, are what make me conscious, how come I am less conscious when asleep? And less than that at the moment of death. I have all the same atoms in the same configuration, right?

  9. Issue A identifies the entire problem: The proponents have failed to define consciousness. Lacking that, it allows them to assign it to anything. So the whole argument is meaningless.

  10. I personally knew some people who were proponents of panpsychism. They were always proposing it, but never explaining it. That’s because their epistemology apparently followed their metaphysics: everyone is aware of the truth of panpsychism on some level, but full knowledge is limited to those who are a little more complex and well-arranged than me.

  11. “Ultimately, he added, “The impact of panpsychism isn’t so much to answer these questions, but to suggest continuity: don’t expect to find a discontinuous boundary somewhere between the simplest animal that is conscious and the most complex animal that isn’t.” Roelofs says there isn’t a line that one could draw: “even if some sorts of consciousness are so simple that it’s more useful for us, in practice, to treat them as ‘mindless’, nevertheless the differences are ultimately just matters of degree.””

    This is quite accurate. However, it presents no problem at all for mainstream science. Given current understanding of many fields of scientific inquiry, especially biology, this is exactly what one would expect. It’s the same quandary you have with drawing lines between species. From a distant enough perspective it’s easy to draw sharp lines. But the closer you get the more difficult it becomes until you have to make what amounts to arbitrary distinctions to be able to draw that line.

    This is a standard tactic of wooists. Describe a problem that isn’t actually a problem and claim your theory provides an explanation that uniquely leads to an ethically superior interpretation, that has actually already been arrived at by many others via many different paths.

  12. If there is a reasonable mixing of material in the surface layer of the world then many of the atoms in my body previously belonged to larger collections, including ancestor plants, animals, and people. Now since, by observation(!), I cannot identify ‘previous consciousnesses’ then this consciousness of atoms must be pretty anonymous small stuff, and nothing worth worrying about.

    1. The corollary of which is, of course, that some of your drinking water was once Shakespeare’s urine.

  13. “Panpsychism, the idea that inanimate objects have consciousness, >gains steam in science communities<."

    When the title flat out says it's more heat than light…


    Salon is awful.

    1. Yes: “…Panpsychism……gains STEAM…”
      No, it’s still FOG.
      It’s just thicker than ever.
      Or else its advocates are.
      Not the exclusive “or “—> could be both, likely both.

  14. You’d think the basic problem with panpsychism is how much our conscious and unconscious thinking is goal-directed – there’s an “aboutness” to thoughts that is heavily rooted in our biology. Consciousness without biology makes no sense whatsoever!

  15. You have grammar which includes the 1st person and the 3rd person neuter. “I am in pain” vs. “My hair is on fire.” Descartes doesn’t help because now we have a “mind” where my “pain” is located, and a physical world where my hair is located. Materialists come along and equate my “mind” with my brain, and now my “pain” is some kind of brain activity (even though the criterion by which we determine how someone is in pain has nothing to do with testing their brain activity, in contrast to say a brain tumor).

    So panpsychism comes along and tries to keep the materialism (no “mind space”) but wants to ontologize the 1st person, so everything is both a 1st person and a 3rd person, and inanimate objects are basically like victims of Medusa. The problem is that there is not a lot that you can really do with the 1st person with respect to say a rock, without some kind of fairy story about how it used to be a troll or something. You have animism, but that is actually a complex subject, and it comes about by using 1st person language derived from interpersonal relationships and imposes them on inanimate objects (like children playing with dolls).

    Its not at all clear that the sentence “I am in pain” is anything like “my hair is on fire” in that the second sentence refers to an object and specifies a physical condition of that physical object. It is not clear that there is something referred to as “I” nor is there something referenced by “pain”. I would note that when you go to the doctors with an injury, they ask where the pain is, and you don’t generally point to your brain (although you might point to your head if your hair burned off).

    If anything is true about naturalism, it is that there is no inside. If you look at language, it is always dualistic, inside/outside, good/bad, black/white, etc. When you try to extract some literal meaning of some expression (inherently dualistic), it doesn’t work where not only is there no true inside, but where all things interpenetrate and intersect (hence the capacity to construct space and time). Yes, there is inside a cell wall, but if you look at a cell wall, first it is constructed, second it is constantly in exchange with its environment, and the cell “dies” when the wall is dissolved. A cell is not an illusion, but there is no ontological or categorical distinction between “inside” and “outside” a cell in comparison to say a Cartesian mind.

  16. Granted, this discussion is not one that I would normally feel qualified to contribute to.
    But here we are sort of speaking about how words are defined, and I am a dictionary enthusiast, especially since English was not my primary childhood language.
    If we go with the EOD, which I always do, consciousness is awareness, more or less.
    more specifically, it is “The state or fact of being mentally conscious or aware of anything.”
    We can take away or return an animal to consciousness through administration of anesthesia. The mechanisms of that process are reasonably well understood. Additionally, it is quantifiable. There is measurable electric activity involved.
    None of the definitions provided in the OED can apply to a rock or to water. Not remotely.
    If they are arguing for some sort of intangible cosmic energy in such things, they need to find a better term than consciousness, which already means a different specific thing.

    Or, I might be completely misunderstanding the conversation, as I tend to do with the ones on free will, which I see from a sort of simple and pragmatic perspective.

  17. The “hard problem” should instead be called the “hard fact” – the fact that an objective description of a person doesn’t convey subjective information about their experience. Note that this applies even with metaphysical woo-posits like souls; the fact that you have a soul (if it is/were a fact) still tells me nothing about whether you are currently experiencing happiness, sadness, or dreamless sleep. (I cribbed the term “hard fact” from Mike Smith at his blog.)

    1. Have you seen the sculpture known as the “Ecstasy of St. Theresa”? Its not even a description of a person, its a sculpture wrested from the imagination of Bernini. Am I really to believe that it does not convey “subjective information about [her] experience”?

      1. Good point, and I phrased my point badly. I should have said that we integrate objective and subjective information when we experience them together, and then when objective portrayals give us information about subjectivity, we are leaning on that previous experience.

  18. Jerry sez: “My own view, which I derived from Patricia Churchland, is that consciousness is an epiphenomenon of a certain arrangement of living molecules, most of them in the brain. Once you have all the ingredients for consciousness in place (and science is beginning to learn about some of them), then you get the phenomenon of consciousness and the presence of subjective sensation. End of the story; nothing more to find out. To me, there’s nothing more to the explanation than that: once the components are there, the being is conscious”

    It’s interesting you think there’s no further story to be told about why and how specific neural and cognitive goings-on – the neural/functional correlates of consciousness (NCC) – entail the existence of conscious experience for the instantiating system. Getting that story fleshed out is the project of explaining consciousness that so many are embarked on, something that would help complete a naturalistic picture of ourselves. Obviously panpsychism is a non-starter, but there are certainly clues in the NCC having to do with representing the world, including the body, in service to action control. One stab at the story in the Journal of Consciousness Studies (JCS), in the context of the major explanatory contenders, is at

    Sean’s paper mentioned by Vampyricon above is part of a forthcoming special issue in JCS on Phillip Goff’s panpsychism. Should be interesting to see if Goff gets any takers.

  19. “Others might think that chairs have consciousness, but of an incredibly diffuse sort: because there’s no brain or nervous system, there’s no order or structure to the chair’s experience, just an undifferentiated blur.” – Luke Roelofs

    Sounds like a psychedelic trip when one “feels it all as one great blooming, buzzing confusion.” (William James referring to a baby’s perceptual experience of the world). Well, actually, it’s panpsychism which seems to have sprung from a dope dream.

    “Panpsychism is surely one of the loveliest and most tempting views of reality ever devised; and it is not without its respectable motivations either. There are good arguments for it, and it would be wonderful if it were true—theoretically, aesthetically, humanly. Any reflective person must feel the pull of panpsychism once in a while. It’s almost as good as pantheism! The trouble is that it’s a complete myth, a comforting piece of utter balderdash. Sorry Galen, I’m just not down with it (and isn’t there something vaguely hippyish, i.e. stoned, about the doctrine?).”

    (McGinn, Colin. “Hard Questions: Comments on Galen Strawson.” Journal of Consciousness Studies 13, no. 10/11 (2006): 90–99. p. 93)

  20. Some combinations of elements do have the ability to induce unconsciousness. Would that mean they possess the property of both consciousness and anti-consciousness? I would prefer my anesthesia to be consciousness free and my beer to have just a taste of a lesser consciousness.

  21. Unexplained peculiar phenomena lead to metaphysical speculation about the nature of this universe. Take, for instance, the licence plate number of the car in which Archduke Franz Ferdinand was killed in 1914.

          1. The licence plate number is very peculiar nonetheless. Given the ranges available in the Austrian Hungarian empire at the time, it is the only that makes a reference to the end date of the war. And if World War I was just an insignificant historical event, you might apply the law of large numbers and call it coincidence. But it is not, so that is problematic.

            1. It doesn’t make reference to the end date of the war. The licence plate is not a date at all, but even if it were, the last number is 118, not 1918 or even just 18.

              1. Not really. The first four characters are all letters. The letter I is not the number one.

                Also, the Austrians signed their armistice on 4th November.

                Also, in Austria, they speak German. The German for “armistice” is “waffenstillstand” which does not begin with an A.

                Also, and this is the killer blow: nobody in 1914 knew when the war was going to end.

  22. Panpsychism arises from what I call labelism. Labelism is the belief that what matters is how you label things. By concentrating on the labels, you can lose sight of the real problem you are trying to solve. Richard Feynman told a story of how he had to review physics text books for school children. In one such book he came across the question “what makes it go?” and there were pictures of things like clockwork toys and motor cars and sailing boats. In each case, the answer given was “energy”. Feynman points out that this is a content free answer: you might as well say “magic”.

    The panpsychism use consciousness in the same way as the text book. It’s a magic word and they think they have gained an insight if they can label everything as “conscious”. No, they can’t: in fact, by doing so, they render the word meaningless.

    Your point (b) is actually the entire problem of consciousness. The real problem is why do humans have such a radically different experience of the world compared to rocks and typewriters. It doesn’t matter if we label the component atoms as conscious or not: it’s that difference in experience we need to explain. Whatever properties you ascribe to an electron cannot be the explanation of consciousness because the electrons are the same in typewriters and people and yet there is a radical difference in the way they interact with the world.

    I think your second (c) is incorrect, by the way. I think electrons have been observed in meticulous detail and no such thing as consciousness has been found in them. In fact, it is pretty much a foundation of modern physics that electrons are interchangeable. There’s no room for consciousness in them. I think panpsychism is disproved by scientific observation.

    1. I believe someone called them curiosity stoppers, or semantic stop signs.

      As for d), the thing with claiming something is untestable is that the universe has a nasty habit of surprising you. (The paper I’ve linked in a comment above would be relevant.)

    2. n fact, it is pretty much a foundation of modern physics that electrons are interchangeable.

      Some Big Physicist (TM), possibly John Wheeler, proposed a fairly implausible theory, that the universe contains only one electron, and it travels in a “higher” dimension which only briefly interacts with out universe in a few (3 or 4) dimensions. When the ur-electron is travelling through our dimensions of the universe in a positive time-like direction, we perceive it as an electron ; when the ur-electron is travelling through our dimensions of the universe in a negative time-like direction, we perceive it as a positron.
      The observed fact that all electrons and positrons have the same mass, and only differ in charge is then neatly pushed behind the man behind the curtain.
      (Nobody, including Wheeler, thinks Wheeler was being serious. No doubt the Archimedes Plutonium and the Electric Universe kook have woven this into their neo-religions. Repeatedly.

  23. To me, there’s nothing more to the explanation than that: once the components are there, the being is conscious.

    I think you need to be explicit that one of the necessary components of “consciousness” (whatever that is) is a sufficiently flexible and wide spread degree of communication between the more-or-less complex components of your conscious organism.
    There’s a second corollary hidden in there too – the components need to have a sufficiently complex internal state that it can have some information to communicate to another (more-or-less similar) component.
    The call for communication is prompted by thinking about ants and other hypersocial insects. While these clearly have complex components (ants) which themselves exhibit a degree of consciousness, it is a lot less clear that the ant colony itself has consciousness. Ants certainly communicate one to the other. But most of that communication is fairly inflexible – pheromones, some gestures. There’s not a lot of communication that can adapt itself to the situation this minute ; it is quite low bandwidth communication.
    Similarly, sensory-motor nervous systems also have fairly low bandwidth – one cell talks until another in a mostly linear network, and says things like “contract” or “alarm”. But when you get into a CNS, the number of connections (the complexity of the graph of connections) can go up rapidly, and by the dictum that “what fires together, wires together” the network connectivity can alter on a relatively rapid timescale – a timescale within the experience of an organism, not of an evolving population.

    My second point about the complexity of the internal state of the “component” makes it necessary to have relatively complex components. If the components are to have an internal state, then receive an input from another component, and modify their internal state in response to that input, then send an output of their own (e.g., firing part of the motor-sensory nervous system), then the component is going to need a considerable number of internal states available to it, which do not interfere drastically with the components internal structure. I think back to physics class, building astable, then monostable, then bistable oscillator circuits – the building blocks of information processing and storage, requiring a minimum of 7 components and 9 connections each.
    You can get that complexity from an entire cell ; you can get most of it (with external assists) in the interactions of DNA/ RNA strands in a virus particle. But, to have such complexity within an electron (with a total of about 8 parameters to entirely describe it). To paraphrase Richard Feynman, “there’s not that much room at the bottom” – you need one of the middling floors, at least.

    Panpsychism itself is arrant bullshit, but it does help focus on some interesting questions. What is the minimal complexity of a network that can exhibit “consciousness”? What is the minimal complexity of a component that can usefully participate in a “conscious” network?
    It remains an open question (to me) if we will find the answers to those questions by deductive reasoning, or if we find out by accidentally creating a conscious system. Anyone care to take the bet? It’s quite important – a whole six-pack, not just a single beer.

    1. Along the same lines as your thinking, I have suggested that three basic requirements for information processing are:

      1. Nodes that can perform some logical/mathematical operation.
      2. A means of channeling signals between such nodes.
      3. Amplification. (A means by which a low energy input can result in a relatively high energy output.

      One can google “youtube domino adder” to see an entertaining example of these three basic functions. 1 and 2 should become obvious by watching the video. Amplification is the result of the stored potential energy in an upright domino being susceptible to a slight tap turning the potential energy into a relatively large amount of kinetic energy.

      Similarly, the neural networks in our brains have the same basic features:

      1. Summation of inhibitory and excitory inputs.
      2. Channeling signals through axons.
      3. Electrochemical amplification of low energy synaptic events into relatively high energy action potentials.

      As far as your bet, I doubt that humans would ever create a conscious machine either by accident or by straightforward design. I would expect a huge amount of trial and error and I would expect initial attempts to result in ‘insane’ creations, which raises ethical issue.

      1. I remember hearing about logic gates operated in “domino space”, and having a good chuckle.
        I wouldn’t bet that we haven’t already created a “conscious” machine, but since it hasn’t had the communications flexibility to tell us about it’s poetry (whatever) it has been switched off. Perhaps on a daily basis.
        Why am I thinking “William Gibson” thoughts. Or Harlan Ellison – “I have No Mouth And I Must Scream” is specifically echoing in my head. Time for a brain-enema.
        I wouldn’t expect humankind to worry overmuch about the ethical concerns. That’s never been high on the list of average human concerns (as opposed to academia’s concerns).

  24. Panpsychism seems to be pantheism (God is in everything) for atheists. If there is no divine presence, people want some sort of universal commonality to replace it.

Leave a Reply