Tendencies and other realizables in Medical Information Sciences

Monist, The, Oct, 2007 by Ludger Jansen

1. Introduction

1.1 Why Tendencies Are Important for Medical Information Sciences

It would sound a bit odd if a medical scientist were to describe his work as research on certain special sorts of entities called 'tendencies'. Nevertheless, searching the standard Medline database of medical research literature yields 48,884 hits for the word 'tendency' together with an additional 4,720 hits for its plural. This is quite something, especially if one takes into account also the figures for related terms such as 'disposition' (20,991 hits) and 'propensity' (9,639 hits). (2) The entities described as tendencies play an important role in medical terminologies under the heading of medical findings. Such findings are, for example, a psychopathic tendency, a suicidal tendency, the tendency to bleed, or the thrombophilic tendency. Many medications are designed to prevent the realization of tendencies. A patient "with suicidal tendency" will be treated in such a way that suicide events will be less likely to occur. (3)

In the light of these facts, it is quite astonishing how little information can be found about tendencies in the major medical terminologies such as the National Cancer Institute Thesaurus (NCIT) or the Unified Medical Language System (UMLS). (4) The UMLS Metathausaurus comprehends some 5 million terms from more than 100 different controlled terminologies and biomedical classifications. Among these terms are such items as 'entity', 'event', 'property', 'mental process' or 'value', not however 'tendency', though the latter term does appear in 23 places within more complex terms that are included (such as Tendency to nausea and vomiting) or within definitions (as in "tendency of a drug, with repeated use, to become less effective [...]," one of the definitions given for Drug Tolerance). (5) The NCIT, too, lacks an entry Tendency. It does, however, contain an entry Disposition, which is defined as follows:

   Disposition--the tendency of something to act in a certain manner
   under given circumstances resulting from natural constitution;
   nature; quality; orderly arrangement.

It is not clear what the semicolons are intended to signify in this definition. The terms that are enlisted with semicolons between them do not seem to be synonymous: a nature is distinct from a quality, and both are distinct from an orderly arrangement. Thus, contrary to the official intention of the NCIT, (6) the term 'disposition' in the NCIT seems not to signify a unique thing, but rather a somewhat confused bundle of things. Moreover, the NCIT subsumes Disposition under the heading Conceptual Entity and not, as one would expect, under the heading Property or Attribute. Surprisingly again, NCIT contains no sub-items of Disposition, though it seems to be obvious that all tendencies "to act in a certain manner under given circumstances resulting from natural constitution" (for example, Tumorigenicity or Lipophilicity) should be listed as sub-items here.

Given the widespread occurrence of words like 'tendency' and 'disposition' in the medical literature it would be very desirable for the terminologies to reflect this importance by adequately representing these subtypes. This is because one of the most important uses of such terminologies is the annotation of research literature in order to enhance information retrieval. Also, the truth of statements like Tumorigenicity is-a Tendency should be reflected in subsumption relations between the corresponding terms in order to enhance automated reasoning.

1.2 Previous Work

Like dispositions, tendencies are causal properties. Standard accounts characterize a tendency as "an entity which can be counteracted by other tendencies" or as "a potentiality which may be exercised without being realized." (7) The first of these characterizations being circular, and the second introducing three new undefined terms, these definitions are insufficiently rigorous for the purposes of information systems which are designed to support computational reasoning. Thus we have to go further. While discussion of tendencies can be traced back at least to Aristotle and to what he says on dynamis, physis, and hexis, (8) there is comparatively little discussion of tendencies in the recent philosophical literature. (9) An exception is the work of Daniel von Wachter, who has argued that the ontology of tendencies may help in ontological engineering. (10) Von Wachter defines a tendency as "a bias in the world at a certain time to carry on in a certain way" (.p. 111). His account of tendencies, however, gives rise to the following three problems:

a. Who or what is the bearer of tendencies? In von Wachter's eyes, it is a state of affairs which is the bearer of a tendency. States of affairs are, in a nutshell, all those complex entities that can be described in that-clauses. Examples are the state of affairs that patient #0004 has red hair, or that patient #0012 is slightly green in the face. By ascribing tendencies to complex entities like state of affairs one gains purchase on the circumstances necessary for a certain outcome. Often, over and above the presence of a certain tendency, other necessary conditions have to be fulfilled to trigger the realization process. Such conditions should not be neglected. But in medicine, tendencies are often ascribed not to states of affairs, but to patients, i.e., to concrete things, independent continuants existing in time and space. It is the patient, not some state of affairs, who has the suicidal tendency or the tendency to bleed. And it is patients, and not states of affairs, who need to be healed. Here I join with those ontologists who distinguish between forces and tendencies: forces are always related to some body they act on, thus the are something relational; tendencies, in contrast, are properties of single concrete things. According to this picture, forces are not themselves tendencies, but they bring about tendencies in the things they act upon. (11)