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*To*: fom@math.psu.edu*Subject*: FOM: Friedman on defending specialized subjects*From*: Stephen G Simpson <simpson@math.psu.edu>*Date*: Wed, 28 Jul 1999 16:34:09 -0400 (EDT)*Organization*: Department of Mathematics, Pennsylvania State University*Reply-To*: simpson@math.psu.edu*Sender*: owner-fom@math.psu.edu

Dear FOM, The ongoing discussion of ``applied recursion theory'' is interesting and valuable, and I want to continue it. However, the discussion is in danger of becoming too specialized for a wide audience of f.o.m. professionals such as exists here on the FOM mailing list. I have been wondering how to deal with this problem. Therefore, I was delighted this morning when Harvey Friedman telephoned me to offer his reactions. As usual, Harvey presented some fascinating insights which are of general intellectual interest, transcending the relatively narrow subject at hand. I now want to share these general insights with you. Harvey intends to post his own elaboration of these points later, perhaps tomorrow. Best wishes to all, -- Steve 1. DEFENDING SPECIALIZED SUBJECTS Harvey's first remark to me was that the ongoing discussion of ``applied recursion theory'' (not limited to the FOM list) has been following a typical, general pattern that is often observed in academic/intellectual life. Here is part of the pattern that Harvey sees. a. Some brilliant, fundamental insights lead to the creation of a new academic discipline, call it subject X. (One has in mind the insights of G"odel, Turing, et al which led to the creation of recursion theory.) The subject enjoys some spectacular initial successes which are of great interest to a wide audience. b. Subsquent practitioners of subject X invest a huge amount of energy in the development of new concepts, structures, research directions, methods, etc., with great commitment and dedication. By a combination of scholarly achievement and political skill, they establish subject X as a strong presence in the academic landscape: publications, hiring, promotion, tenure, etc. c. Because subject X has now become well established, the concerns and methods of subject X are now free to develop independently, as an end in themselves. Eventually these concerns and methods become so specialized that nobody except the most dedicated specialists are able to make use of them or derive any perceived benefit from them. d. Scholars in related fields begin to question or criticize subject X by saying that it may be overdeveloped, too specialized, no longer relevant to the original fundamental concerns that gave rise to it, etc. e. Practitioners of subject X defend it on the grounds that i. subject X is beautiful and important for its own sake, as a kind of pure art-form or sport; ii. the insights achieved by subject X are so stunning that they are bound to have many valuable applications outside the relatively narrow confines of subject X itself. f. The critics respond by saying that i. subject X is beautiful only to the practitioners; ii. the insights achieved by subject X have not actually addressed any relevant concerns, beyond the initial successes; iii. the more recent development of subject X has moved it farther away from the initial successes, thus making it ever less likely to yield anything of general interest. g. In the best case, the practitioners of subject X may respond to the critics by reforming or redirecting or recasting subject X in significant new ways, thus giving subject X a new lease on life. This cycle of criticism, reform, criticism, reform, ... can continue indefinitely, to the great benefit of subject X and related academic subjects. h. Another possibility is that the practitioners of subject X may be unwilling or unable to change directions. In this case, their response to the critics may be of a different nature. i. For instance, the practitioners may respond by insisting that, even if the *insights* and *results* achieved by subject X have not been particularly valuable for outsiders, the *concepts* and *methods* of subject X are of such great general interest that it would be a shame not to continue developing them, both for their own sake and for the sake of future possible applications, whose nature cannot be predicted. j. The practitioners of subject X may then run into an intellectual impasse, because in order to advance their argument, they need to define or delimit the set of concepts and methods that they are referring to. If they define them too narrowly, the claim of general interest becomes implausible. If they define them too broadly, the claim of subject X to ownership of these methods and concepts becomes ridiculous. The practitioners of subject X may need to walk a fine line, and this may prove difficult or impossible. k. The practitioners of subject X may then get upset, accuse the critics of unfairness, attempt to suppress discussion, etc etc. l. (to be continued) It will be interesting to see how the debate on ``applied recursion theory'' plays out as an instance of this general pattern. 2. LACK OF EXAMPLES Harvey's second comment to me is more specifically about recursion theory, namely the ``pure'' study of recursively enumerable sets and their degrees of unsolvability. It has to do with the lack of examples. This is a point that Harvey has made previously here on FOM, but here it is again. Usually, when mathematicians undertake an intensive investigation of some specific structure or class of structures, the need for such an investigation has already been motivated by a set of specific, natural examples showing the richness and interest of the subject. For instance, group theory was motivated by a wealth of examples such as matrix groups, permutation groups, symmetries of geometrical figures, etc. Contrast this with the r.e. sets and degrees that are so much beloved by recursion theorists. The only natural examples known to date are the original ones, i.e. the halting problem and the complete r.e. degree. Thus there is really only one example, and that example is highly atypical of the way the subject has developed. It is reasonable to wonder whether this lack of examples may indicate some sort of defect or imbalance in the subject. Harvey has some ideas, which I don't fully understand, about how to view this as an instance of a general pattern in academic/intellectual life. Perhaps Harvey will elaborate later. In the meantime, let me ask the recursion theorists to respond straightforwardly to the following question: What is the *real* reason for your emphasis or preoccupation with pure structural questions concerning the lattice of r.e. sets and the semilattice of r.e. degrees? Some reasons that have been given in the past are: the beauty of the methods, applications to computer science, possible applications to pure mathematics, etc. But somehow these reasons do not ring true. I somehow feel that these are not the *real* reasons. I am asking for the *real* reason. -- Steve

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