Path: utzoo!attcan!uunet!husc6!mailrus!cwjcc!tut.cis.ohio-state.edu!rutgers!elbereth.rutgers.edu!harnad From: harnad@elbereth.rutgers.edu (Stevan Harnad) Newsgroups: comp.ai Subject: Re: Biological Categorization Summary: Why I Am Not A Positivist Message-ID: Date: 24 Jan 89 20:34:01 GMT References: <3039@uhccux.uhcc.hawaii.edu> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 173 lee@uhccux.uhcc.hawaii.edu (Greg Lee) of University of Hawaii wrote: " You underestimate Positivism, of which in fact your theory appears to be " a species. Here is a passage from Moritz Schlick's "Positivism and " Realism" (1932/3,in Ayer, _Logical Positivism_): "But when do I " understand a proposition? When I understand the meanings of the words " which occur in it? These can be explained by definitions. But in the " definitions new words appear whose meanings cannot again be described in " propositions, they must be indicated directly: the meaning of a word " must in the end be _shown_, it must be _given_. This is done by an act " of indication, of pointing; and what is pointed at must be given, " otherwise I cannot be referred to it." " Except that even Schlick allows grounding in *possible* experiences, " I see no notable differences from your views. For a recent argument " against applying this approach to natural language, see Chomsky's " review of Skinner's _Verbal Behavior_. Although I do confess to a lingering sympathy for certain perfectly valid features of positivism (the "P" word), as well as for verificationism and the 18th century empiricism from which they grew (I think positivism was rejected by psychologists just as hastily, superficially, unselectively and uncritically as it was first accepted by them), I am nevertheless no positivist, as is quite evident from the representational model I am proposing. Nor am I a behaviorist (as the above quote also seems to imply). The positivists were concerned with MEANING (especially the meaning of scientific statements): What statements are and are not meaningful, and in what does their meaning consist? I, on the other hand, am concerned with categorization: How do we SORT and LABEL categories and USE the category labels in statements about categories? The positivists claimed that only "observation statements" -- or statements from which observation statements could be readily derived -- were "meaningful." I certainly don't say anything of the sort. In fact, I happen to find most of the very statements that the positivists wished to reject as meaningless and metaphysical to be perfectly meaningful, with their terms perfectly well grounded (in MY sense, i.e., consisting of the labels of categories that were grounded in the labels of categories that were grounded in... the labels of concrete sensory categories that we can sort and label directly). Moreover, most of what the positivists themselves said becomes trivially obvious and no longer "positivistic" in any substantive sense if restated in terms of categorization rather than meaning, as the following transcription shows: "But when can I sort a category described by a label-string? When I can sort categories for the labels which occur in it? These can be described by more label-strings. But in the label-strings new labels appear whose categories cannot again be described by still more label-strings [on pain of infinite regress]: the members of a category must in the end be actually sorted." This is simply a statement of a version of what I've called "the symbol grounding problem," plus a fairly obvious constraint on its solution in the case of categorization. That the positivists too noticed this problem does not mean that all solutions to it are therefore positivistic. -- Not that the positivists even offered a solution, mind you, for "pointing" is certainly no solution to a cognitive theorist, who must provide the underlying causal mechanism that governs the success of the pointing, i.e., a representational theory! Successful pointing to the right category members is the behavioral capacity the cognitivist must explain! The philosopher simple takes it for granted. Behaviorism likewise has as little to offer a cognitive theorist as does positivism. It's not helpful to know that a subject's successful pointing performance was "shaped" by his reinforcement history: The cognitive theorist must come up with the internal structures and processes that were responsible for that success, given those inputs and that feedback from the consequences of MIScategorization. (To this extent one can of course agree completely with Chomsky's critique of Skinner; but the rest of Chomsky's argument against learning and empiricism -- the celebrated "poverty of the stimulus" argument -- has so far only been applied to and provisionally supported in the special case of certain syntactic categories, certainly not categorization in general!) [Among the objections to positivism was one that was directed at empiricism as a whole and has lately been championed by Chomskian nativists like Jerry Fodor: the problem of "abstraction" or "vanishing intersections" -- the (alleged) fact that one cannot ground abstract terms such as "goodness" or "truth" in the features shared by concrete sensory instances (such as "this good boy" or "that true statement") because NO FEATURE is shared by all the sensory instances: their intersection is simply empty. I, obviously, am not persuaded by this claim (or the radical nativism about categories that accepting it would entail -- what I've dubbed elsewhere the "Big-Bang Theory of the Origin of Knowledge"). Let me note in passing only that this claim has often been made, but never tested, because testing whether sensory intersections actually vanish is not in the philosopher's line of work. Other reasons for rejecting positivism came from some of the Wittgensteinian considerations, likewise untested, that have surfaced a few times in this discussion (e.g., that the category "game" has no invariant features).] Finally, about the "possible" experience that my theory supposedly does not allow: On the contrary, MOST of the grounding in my theory is based on possible rather than actual direct sorting. In fact, even categories that are unverifiable in principle may be perfectly well-represented categories in my theory. As an example, I will use the category of a "peekaboo unicorn," which should be meaningless to a verificationist. But first, let me just quickly sketch the representational theory (for details, see the last chapter of "Categorical Perception: The Groundwork of Cognition"): There are three kinds of internal representations. "Iconic Representations" (IRs) are internal analogs of the proximal projections of objects on the receptor surfaces. IRs subserve relative discrimination, similarity judgment, and tasks based on continuous analog transformations of the proximal stimulus; but because they blend continuously into one another, IRs cannot subserve categorization. Categorical Representations (CRs) are IRs that have been selectively filtered and reduced to only the invariant features of the proximal projection that reliably distinguish members of a category from whatever the confusable alternatives are in a specific "context" or sample of alternatives. CRs subserve categorical perception and object identification. CRs are also associated with a label, the category name; these names are directly "grounded" in their IRs and CRs and the objects these pick out. The labels are also the primitives of a third kind of representation, Symbolic Representations (SRs). SRs can be combined and recombined into strings of symbols that form composite SRs and likewise pick out categories, as grounded in IRs and CRs. CRs pick out categories by direct perceptual experience; SRs pick them out by symbolic description, with its primitive terms ultimately grounded in perceptual representations. SRs subserve natural language. Here is an example of how my "grounding" scheme would work. The example is recursive on whatever the primitive categories actually are (they are certainly not the ones I actually give here): Suppose the category "horse" ("H") is grounded in the categorizer's having learned to sort and label horses by direct perceptual experience, with feedback from mislabeling. IRs have been formed, as well as CRs that will correctly sort horses and non-horses (within a sampled context of confusable alternatives). Suppose the category "having stripes" ("S") is similarly grounded, with IRs and CRs. Suppose also that the category "having one horn" ("O") is similarly grounded, with IRs and CRs. With the IRs and CRs possessed so far, a categorizer could sort and label H's, S's and O's from direct experience. Now introduce the following Symbolic Representation: "Zebra" ("Z") = H & S. It is evident that, armed only with the IRs and CRs in which "H" and "S" are grounded, not only WOULD [note the "possible experience"] a categorizer now be able to sort and label zebras correctly from the very first time he encountered one (if he were ever to encounter one), but he also now has a new grounded label "Z" that can henceforth enter into further grounded SRs, in virtue of the IRs and CRs in which it is grounded. Let's take yet another nonpositivistic step forward: "Unicorn" ("U") = H & O. This category, being fictional, will NEVER be encountered, yet it is perfectly well-grounded. Let's go still further: By similar means I could define a "Peekaboo Unicorn" which is not only a horse with one horn, but has the property that it "disappears" whenever any "sense-organ" or "detecting device" is trained on it (all these further categories likewise being grounded as above). Hence a "Peekaboo Unicorn" is a category that is unobservable and unverifiable IN PRINCIPLE, yet perfectly well-grounded in IRs, CRs, sensory experience, and actual objects. Such is the power of a viable grounding scheme. So do you still think I'm a positivist? -- Stevan Harnad INTERNET: harnad@confidence.princeton.edu harnad@princeton.edu srh@flash.bellcore.com harnad@elbereth.rutgers.edu harnad@princeton.uucp BITNET: harnad@pucc.bitnet CSNET: harnad%princeton.edu@relay.cs.net (609)-921-7771