As things stand today, Murphy explains, psychiatry relies on four criteria to validate a diagnosis: natural history (of a syndrome: its characteristic clinical course and outcome); family history (including genetics); differential response to treatment; and laboratory findings. The problem with these criteria, notes Murphy, as emblematically enshrined in the DSM, is a failure to give pride of place to "causal information," apart from the lack of explicit reference to requisite normative considerations (e.g., a model of rationality). We are left, in other words, with the picture of valid syndrome on the order of a "collection of symptoms that cluster together" but without the kind of information essential to a medical (or biological) model of psychiatric disease/disorder. Put differently, "The concepts of clinical phenomenology are notoriously vague, imprecise, unquantified. By limiting the data gathered in diagnosis to the salient and easily identifiable signs and symptoms of clinical phenomenology, the DSM-IV-TR [fourth ed., revised text] scheme ignores a wide range of other data about mental functioning that can be gathered by psychometric techniques and by methods used in cognitive science and neuroscience."
While I'm not fond of Murphy's conception of psychiatry and do not share his philosophy of mind assumptions about the nature of the "mental" or the inherent liabilities of "folk psychology" for that matter, there is much of value in this book whether or not one agrees with the (3) theses (p. 11) he sets out to defend. As in the aforementioned SEP entry, Murphy provides us with excellent conceptual clarification of such terms as "objectivism" and "constructivism" and the projects of "naturalization" and "mechanization" as they apply to psychiatry and psychology. And he makes a devastating critique of the DSM-IV's concept of mental disorder, including the fact that it "permits exclusively behavioral criteria for diagnosis, leading to a failure in many cases to distinguish mental disorders from 'problems in living'--fully comprehensible, indeed wholly expected, reactions to stressful circumstances." Whatever one thinks of Murphy's "medical model" for psychiatry, I think it's hard to quibble with his contention that psychiatry "need[s] both a theory of rationality and a theory of the mechanisms underpinning rational thought and behavior, so that departures from both can be assessed, explained, and treated." Murphy argues that, while there is not a convincing mechanistic model of reason along, say, computational lines, the prospects for a naturalistic rationalization project look better: "But agreement on the naturalistic rationalization project will require equilibrium between folk theory, various sciences, and naturalistic philosophy of mind and epistemology." In a review of the book, Luc Faucher well summarizes Murphy's frank and important conclusion about the implications for a purely scientific model of psychiatry:
"According to Murphy, one can naturalize reason (that is, one can provide a story concerning the possible evolved epistemic function of rationality), but not mechanize it. The consequence of this is that "[t]he assessment and treatment of these disorders [like delusion or alcoholism] usually requires an explicit model of what good reasoning is. If rationality is a normative notion, the model must be in part normative. Since this model is normative, it undermines the pretensions of the medical model to purely positive science" (153). However Murphy reminds us that this concession is not an endorsement of the anti-psychiatry's position of people like Szasz, because it applies only to a limited number of mental illnesses, and the norms in question are not social norms, but rather rationality norms."
Cross-posted, with some modifications, at the Medical Humanities Blog.