dave@cogsci.indiana.edu (David Chalmers) (10/06/90)
Here are some thoughts on "emergence". Nothing definitive, but an attempt to get at the psychological core (or cores) of the notion. Thanks are due to others for providing a stimulating discussion. Emergence is a tricky concept. It's easy to slide it down a slippery slope, and turn it into something implausible and easily dismissable. But it's not easy to delineate the interesting middle ground in between. Two unsatisfactory definitions of emergence, at either end of the spectrum: (1) Emergence as "inexplicable" and "magical". This would cover high-level properties of a system that are simply not deducible from its low-level properties, no matter how sophisticated the deduction. This view leads easily into mysticism, and there is not the slightest evidence for it (except, perhaps, in the difficult case of "consciousness", but let's leave that aside for now). All material properties seem to follow from low-level physical properties. Very few sophisticated people since the 19th century have actually believed in this kind of "emergence", and it's rarely what is referred to by those who invoke the term favourably. But if you mention "emergence", someone inevitably interprets you as meaning this, causing no end of confusion. (2) Emergence as the existence of properties of a system that are not possessed by any of its parts. This, of course, is so ubiquitous a phenomenon that it's not deeply interesting. Under this definition, file cabinets and decks of cards (not to mention XOR gates) have plenty of emergent properties -- so this is surely not what we mean. The challenge, then, is to delineate a concept of emergence that falls between the deeply implausible (1) and the overly general (2). After all, serious people do like do use the term, and they think they mean something interesting by it. It probably will help to focus on a few core examples of "emergence": (A) The game of Life: High-level patterns and structure emerge from simple low-level rules. (B) Connectionist networks: High-level "cognitive" behaviour emerges from simple interactions between dumb threshold logic units. (C) The operating system (Hofstadter's example): The fact that overloading occurs just around when there are *35* users on the system seems to be an emergent property of the system. (D) Evolution: Intelligence and many other interesting properties emerge over the course of evolution by genetic recombination, mutation and natural selection. Note that in all these cases, the "emergent" properties are in fact deducible (perhaps with great difficulty) from the low-level properties (perhaps in conjunction with knowledge of initial conditions), so a more sophisticated concept than (1) is required. Another stab at a definition might be: (3) Emergent = "deducible but not reducible". Biological and psychological laws and properties are frequently said not to be reducible to physical laws and properties. For many reasons, not the least being that the high-level laws/properties in question might be found associated with all kinds of different physical laws/properties as substrates. (A universe without protons and electrons might nevertheless include learning and memory.) There are some problems with this definition, though. Firstly, it's not clear what is gained by trying to explicate emergence in terms of the almost-equally-murky concept of "reduction". Secondly, it seems to let in some not-paradigmatically-emergent phenomena, and it's not clear how some emergent phenomena like (A) or (C) would fit this definition. I think that (3) picks out a very interesting class, but it's not quite the class we're after. It's on the right track, though, I think. The notion of reduction is intimately tied to the *ease of understanding* one level in terms of another. Emergent properties are usually properties that are more easily understood in their own right than in terms of properties at a lower level. This suggests an important observation: *Emergence is a psychological property*. It is not a metaphysical absolute. Properties are classed as "emergent" based at least in part on (1) the interestingness to a given observer of the high-level property at hand; and (2) the difficulty of an observer's deducing the high-level property from low-level properties. The properties of XOR are an obvious consequence of the properties of its parts. Emergent properties aren't. Might as well give this a number: (4) Emergent high-level properties are *interesting, non-obvious consequences* of low-level properties. This still can't be the full story, though. Every high-level physical property is a consequence of low-level properties, usually non-obviously. It feels unsatisfactory, for instance, to say that computations performed by a COBOL program are an emergent property relative to the low-level circuit operations -- at least this feels much less "emergent" than a connectionist network. So something is missing. The trouble seems to lie with the complex, kludgy *organization* of the COBOL circuits. The low-level stuff may be simple enough, but all the complexity of the high-level behaviour is due to the complex *structure* that is given to the low-level mechanisms (by programming). Whereas in the case of connectionism or the game of life it feels that we have simplicity in both low-level mechanisms and their organization. So in those cases, we have much more of a "something for nothing" feel. Let's try for another number: (5) Emergence is the phenomenon wherein complex, interesting high-level function is produced as a result of combining simple low-level mechanisms in simple ways. I think this is much closer to a good definition of emergence. Note that COBOL programs, and many biological systems, are excluded by the requirement that not only the mechanisms but their principles of combination be simple. (Of course simplicity, complexity and interestingness are psychological concepts, at least for now, though we might try to explicate them in terms of Chaitin-Kolmogorov-Solomonoff complexity if we felt like it. My intuition is that this is likely to prove a little simplistic, although Chaitin has an interesting paper that attempts to derive a notion of the "organization" of a system using similar considerations.) And note also that most things that satisfy this definition should also satisfy (4) -- due to our feeling that simple principles should have simple consequences (or else complex but uninteresting consequences, like random noise). Any complex, interesting consequence is likely to be non-obvious. This does indeed fit in with the feeling that emergence is a "something for nothing" phenomenon -- though in a more subtle and satisfactory way than set forth in (1), for instance. It's a phenomenon whereby "something stupid buys you something smart". And most of our examples fit. The game of Life and connectionist networks are obvious: interesting high-level behaviour as a consequence of simple dynamic rules for low-level cell dynamics. In evolution, the genetic mechanisms are very simple, but the results are very complex. (Note that there is a small difference, in that in the latter case the emergence is diachronic, i.e. over time, whereas in the first two cases the emergence is synchronic, i.e. not over time but over levels present at a given time.) We're still not completely there -- it's not clear how (C), the operating system example, fits into this paradigm of emergence. But throwing in a smidgen of teleology should get us the rest of the way. I.e., we have to notice that everything here has to be relativized to *design*. So we *design* the game of Life according to certain simple principles, but complex, interesting properties leap out and *surprise* us. Similarly for the connectionist network -- we only design it at a low level (though in this case we *hope* that complex high-level properties will emerge). Whereas in the COBOL case -- and in the case of much traditional AI -- you only get out what you put in (N.B. I'm not necessarily knocking this: at least here, I'm trying to explicate emergence, not to defend it). And now the operating system example fits in well. The design principles of the system in this case are quite complex -- unlike the other cases that fit (5) above -- but still the figure "35" is not a part of that design at all. So: (6) Emergence is the phenomenon wherein a system is designed according to certain principles, but interesting properties arise that are not included in the goals of the designer. Notice the appearance of the word "goal" -- this is important, any design is goal-relative. So the notion now is quite teleological. I notice that Russ Abbott makes a similar point in a recent posting. Notice, however, that as we've conceded that emergence is a psychological property, we're able to construe teleology in a psychological, non-absolute way. So for our purposes here, we only need the *appearance* of teleology. This is nice, because it allows us to include system where strictly speaking, "design" doesn't apply at all. In evolution, for instance, there is no "designer", but it is easy to treat evolutionary processes as processes of design. On more than one level. We can view evolution as teleological at the level of the gene -- as in Dawkins' theory, for instance. Then the appearance of complex, interesting high-level properties such as intelligence is quite emergent. We also can reconstrue evolution as teleological at the level of the organism (this is perhaps a more straightforward Darwinian view of things). On this construal, the most salient adaptive phenomena like intelligence are no longer emergent, but the goal of the design process. However, this view does open up the possibility of other kinds of emergent phenomena: firstly, non-selected-for byproducts of the evolutionary process (such as Gould and Lewontin's "Spandrels"); secondly and more intriguingly, it allows an explanation for why "consciousness" (or "subjectivity" or "qualia" or whatever) seems emergent. Raw consciousness doesn't not seem to have been selected for, as it doesn't play any direct functional role (though it does have functional counterparts; this is a subtle issue, but remember we're talking about the way things *seem*, not the way they are); but it somehow emerges as a byproduct of selection for adaptive process such as intelligence. It's probably foolish to search for a definitive construal of "emergence": like most psychological concepts, it probably is best construed as a "family resemblance" -- each of the "definitions" outlined above might play some role. Personally, I'm happiest with a combination of (5) and (6) -- with (5) being the "core" variety of emergence, and (6) being a more general variety of which (5) is a special case. -- Dave Chalmers (dave@cogsci.indiana.edu) Concepts and Cognition, Indiana University. "It is not the least charm of a theory that it is refutable."
cpshelley@violet.uwaterloo.ca (cameron shelley) (10/07/90)
In article <62500@iuvax.cs.indiana.edu> dave@cogsci.indiana.edu (David Chalmers) writes: >Here are some thoughts on "emergence". Nothing definitive, but an attempt >to get at the psychological core (or cores) of the notion. Thanks are due to >others for providing a stimulating discussion. > [much stuff deleted...] >(6) Emergence is the phenomenon wherein a system is designed according to >certain principles, but interesting properties arise that are not included >in the goals of the designer. > [a little more...] > >We can view evolution as teleological at the level of the gene -- as in >Dawkins' theory, for instance. Then the appearance of complex, >interesting high-level properties such as intelligence is quite >emergent. We also can reconstrue evolution as teleological at the level >of the organism (this is perhaps a more straightforward Darwinian view of >things). On this construal, the most salient adaptive phenomena like >intelligence are no longer emergent, but the goal of the design process. So far this is a laudible attempt at synthesis of the various contributions but I'd like to insert a comment here. I think the use of the term "designer" is misleading. While intelligence might not be considered emergent at the "Darwinian" level synchronically, it must still be so diachronically. Unlike a 'designer', natural selection can only passively enforce changes and so must wait until the random process of mutation gives it the proper opportunity. Therefore, at the time when a significant enough increase in intelligence occurs, it must be emergent. So intelligence should still be considered emergent in the diachronic sense you mentioned earlier (and I cut out :). The real difference is that the perceiver of emergence and the "designer" need not be the same, us the former, nature (in the past) the latter. Perhaps the defintion could be rewritten: (6a) Emergence is the phenomenon wherein a system is designed according to certain principles, but interesting properties arise that are not *inferable* or directly implied in the goals of the designer. I think this weakens the connection between 'designer' and "system" enough to allow for passive manipulation and separation between 'designer' and 'perceiver' which I would like to see included. [a bit more off here...] > >It's probably foolish to search for a definitive construal of "emergence": >like most psychological concepts, it probably is best construed as a >"family resemblance" -- each of the "definitions" outlined above might >play some role. Personally, I'm happiest with a combination of (5) and (6) -- >with (5) being the "core" variety of emergence, and (6) being a more general >variety of which (5) is a special case. > >-- -- Cameron Shelley | "Saw, n. A trite popular saying, or proverb. cpshelley@violet.waterloo.edu| So called because it makes its way into a Davis Centre Rm 2136 | wooden head." Phone (519) 885-1211 x3390 | Ambrose Bierce
dave@cogsci.indiana.edu (David Chalmers) (10/09/90)
In article <1990Oct7.012523.3828@watdragon.waterloo.edu> cpshelley@violet.uwaterloo.ca (cameron shelley) writes: >While intelligence might not be considered >emergent at the "Darwinian" level synchronically, it must still be so >diachronically. Unlike a 'designer', natural selection can only >passively enforce changes and so must wait until the random process >of mutation gives it the proper opportunity. Therefore, at the time >when a significant enough increase in intelligence occurs, it must >be emergent. So intelligence should still be considered emergent in the >diachronic sense you mentioned earlier (and I cut out :). Depends on how you construe the teleology of the evolutionary process. Of course there's no real teleology there, but psychologically we can construe it an at least three different ways. My original post suggested two of these ways, your response suggests a third. First way: Teleology at the level of the gene. Goal: get genes to replicate. At this level, intelligence is emergent. Second way: Teleology at the level of the organism. Goal: get organisms to survive and replicate. This is your suggestion. If the only teleology we impute to the evolutionary process is that of a "natural selector" -- i.e. produce systems that survive and replicate -- then specific functions like intelligence are indeed emergent. Third way: Teleology at the level of the organism. Goal: get organisms to be like X (for some X, e.g. X = strong, fast, intelligent...). Here, we are construing the teleology of the evolutionary process not as that of the natural selector, but as that of the "blind watchmaker". On this view, intelligence is the goal of the evolutionary process, and so cannot be regarded as emergent. The teleology here not being metaphysical but psychological, all these ways of construing it are quite valid. My original post only mentioned the first and third possibilities. The second possibility is also a very reasonable construal, and serves the useful purpose of showing how intelligence can be regarded as emergent without having to descend to the level of the "selfish gene". Sorry for omitting this possibility in my original post. -- Dave Chalmers (dave@cogsci.indiana.edu) Concepts and Cognition, Indiana University. "It is not the least charm of a theory that it is refutable."
gaben@microsoft.UUCP (Gabe NEWELL) (10/11/90)
I have a request and a comment. The request is that someone mail me the first 12 articles off of this group. I don't have access to them and it is frustrating. The second is that emergence seems to be a concept based on a misperception about language or symbolization (I make no claim to having any expertise in understanding either). The misperception is that theories or thoughts about things are not the actual things themselves. Theories are in general very lossy data compression schemes. Emergence is the result of divergence from my model (I think the hierarchical issue is irrelevant - you can get emergence from theorizing about things at the same level of abstraction not just from moving from a lower-level description to a higher level; more specifically emergence is an example of a class of problems which result from failure to recognize that knowledge is inherently lossy as is the whole concern about which is "true" or "right", psychoanalysis or neuro- science, etc...). For example, I have a cat. The cat is furry, and purrs a lot, and makes me happy. I have a very simple description of a cat. Now I have a second cat, and I have a cat fight. Nothing in my model of a cat would have predicted a cat fight. Emergent behavior is NOT an interesting characteristic of the universe, it is an interesting result of how I think about things.
schraudo@beowulf.ucsd.edu (Nici Schraudolph) (10/14/90)
I like David Chalmer's attempt to define "emergence", but I am bothered
by his inclusion of subjectivity ("interesting") and teleology ("unan-
ticipated") in the definition. I believe that this can of worms can be
avoided by using a different ansatz due to Paul Churchland:
"A property P specified by its embedding theory T1 is emergent with respect
to the properties of an ostensibly reducing theory T2 just in case
1. P has real instances,
2. P is co-occurrent with some property or complex
feature recognized in T2, but nevertheless
3. P cannot be reduced to any property postulated by
or definable within T2."
(Paul Churchland, "Reduction, qualia, and the direct introspection of brain
states", Journal of Philosophy 82:8-28, 1985)
Basically, 1) restricts us to actual phenomena, 2) ensures the two levels
of description talk about the same phenomenon, and 3) is the beef of it.
Note that this definition is similar to Chalmer's (2) and consistent with
Reed's "emergence in simple systems" - in other words, it makes almost every
interesting property of a composite system emergent. Now let's throw away
the trivial cases:
An emergent property P is non-trivial iff it is not deducible from
the property or complex feature in T2 that it is co-occurrent with.
Note that the failure to deduce P implies that either T1 or its reduction
to T2 is incomplete. The reference to theories thus nicely formalizes the
subjectivity introduced by Chalmer: P is unanticipated by an observer O pre-
cisely to the extent that it is not deducible in O's theoretical framework.
This seems to be a formalization of Chalmer's (6) - or is there a nuance
that I have missed Dave?
To illustrate all this, the property "is_thrashing" of a virtual memory
(VM) computer system, defined by its embedding theoretical framework
("Paging Science"), is emergent with respect to the theory of non-VM
computing since
1) virtual memory systems can thrash,
2) thrashing is co-occurrent with certain combinations of properties
(viz. memory access patterns) that are recognizable in a non-VM
framework, but
3) there is no concept corresponding to thrashing in a non-VM framework.
This emergence may be non-trivial to the average computer user (who would
be at a loss as to why the system is crawling at a snail's pace), but to
the extent that Paging Science is a well-developed and well-grounded (in
non-VM computing) science it will be trivial to the Paging Scientist.
Not surprisingly, the people that like to talk about emergence are typically
found in fields where the either the theory itself or its grounding in a
potentially reducing low-level theory is underdeveloped, resulting in an
abundance of non-trivial emergent phenomena.
--
Nicol N. Schraudolph, C-014 "Big Science, hallelujah.
University of California, San Diego Big Science, yodellayheehoo."
La Jolla, CA 92093-0114 - Laurie Anderson.
nici%cs@ucsd.{edu,bitnet,uucp}