www.crossingdialogues.com/journal.htm DIALOGUES Crossing Dialogues Association 23 The Implications of Meaning for the Validity of Diagnostic Categories DAVID TRAFIMOW Department of Psychology, MSC 3452 New Mexico State University PO Box 30001 Las Cruces, NM 88003-8001 dtrafi mo@nmsu.edu DIAL PHIL MENT NEURO SCI 2010; 3(1): 23-24 Rodrigues and Banzato (2009) related the validity of diagnostic categories to their meaningfulness and I wish to explore this relation further without attempting to make criticisms. To commence, if a diagnostic category is to be valid, it must mean something. The meaning might not be completely explicit or capable of being understood by non experts but it must be there. Given that diagnostic categories often use non observational terms (e.g., schizophrenia is not observable though particular symptoms might be), it is a fair question to ask from where the meaning of a non observational term comes. Most non observational terms that we use do not have explicit defi nitions or have controversial defi nitions. Indeed, much literature has been devoted to arguing for the superiority of one defi nition of a non observational term over another defi nition. Researchers often even attempt to fi nd empirical evidence to support a favored defi nition. Of course, such efforts are doomed in the long run because defi nitions are not susceptible to empirical fi ndings; defi nitions are not true or false but rather more or less useful. Well, then, consider a non observational term that does not have a completely clear and explicit defi nition; from where does it gain meaning? Most obviously, meaning is obtained via the connection the non observational term has to other terms in the theory. As an example, consider the concept of "mass" from physics. Newton never defi ned the term. Not only does "mass" obtain its meaning from the other variables in Newton's theory (e.g., "force" and "acceleration"), but its meaning is very different as it is used by Newton and by Einstein. Given that "mass" has more than one meaning, which one do physicists use? The answer, of course, is that the winning theory gets to defi ne the term. Because Einstein's theory has better empirical support than Newton's theory, "mass" is defi ned by contemporary physicists according to Einstein rather than according to Newton. So what does all this mean for the validity of diagnostic categories? It seems inescapable that for a diagnostic category to be valid, it has to be meaningful. And for it to be meaningful, the crucial terms must be connected to other terms. Put more generally, the meaning of a diagnostic category depends on the theory that contains the crucial non observational term; the better the theory that surrounds the crucial term, the more valid the diagnostic category that contains it. In turn, this reasoning implies that the process of testing the validity of diagnostic categories is not dissimilar from other science. Because the validity of a diagnostic category depends, to a large extent, on the validity of the relevant theory, there is no way to separate validity assessment from theory testing. Consequently, the same philosophical considerations that are relevant to theory testing also are relevant for assessing the validity of diagnostic categories. Or, if the concern is to choose between alternative conceptions of a diagnostic category, the task ultimately becomes one of choosing between alternative theories that contain the crucial non observational term again a matter of theory testing. I recognize that diagnostic categories often are used in the absence of real theories. The foregoing comments should make it obvious that this is too bad; obviously, theory testing cannot be carried out in the absence of theories and by implication, neither can validity assessment. To Dialogues in Philosophy, Mental and Neuro Sciences DIAL PHIL MENT NEURO SCI 2010; 3(1): 23-24 Trafi mow the extent that strong theories are lacking, valid diagnostic categories also will be lacking, and so the fi rst consideration of concerned researchers should be to have strong theories. 24 REFERENCES Rodrigues ACT, Banzato CM. A logical-pragmatic perspective on validity. Dial Phil Ment Neuro Sci 2009;2:40-44.