Philosophers distinguish “intensional definitions,” which attempt to identify the essence of a term in a sentence or two, from “extensional definitions,” which instead provide a list of exemplars of the term in question. Neither approach is perfect.
Intensional Definition of Interdisciplinarity
As noted earlier, we identify interdisciplinarity with integration. This implies that interdisciplinary research or teaching integrates insights from multiple disciplines – or at least attempts to do so. This also implies that interdisciplinary analysis is focused on questions that no single discipline can provide a complete answer to on its own. It is often thus said that interdisciplinarians investigate “complex” questions. (See Complexity)
Klein and Newell (1998) offer the following widely-quoted definition of interdisciplinary studies:
A process of answering a question, solving a problem, or addressing a topic that is too broad or complex to be dealt with adequately by a single discipline or profession… [It] draws on disciplinary perspectives and integrates their insights through construction of a more comprehensive perspective. (p. 393-4)
The National Academies definition is broadly similar:
Interdisciplinary research (IDR) is a mode of research by teams or individuals that integrates information, data, techniques, tools, perspectives, concepts, and/or theories from two or more disciplines or bodies of specialized knowledge to advance fundamental understanding or to solve problems whose solutions are beyond the scope of a single discipline or area of research practice.
If we will identify interdisciplinarity with integration then we must believe that humans are capable of synthesizing insights from different disciplines. We must not believe, then, that disciplines are “incommensurate,” incomprehensible to people from another discipline. Scholars of Interdisciplinarity often refer to “common ground” theory in psychology: if we can identify some common element in differing insights we can build on this to generate an integrated understanding. Interdisciplinary research strategies often then stress identifying some element of common ground.
Extensional Definition of Interdisciplinarity
Several key characteristics of (much/most) interdisciplinary analysis deserve emphasis:
Interdisciplinary scholars engage deeply with the disciplines that they draw upon. It is not enough to read one article or have coffee with one colleague (though such practices are better than no cross-disciplinary engagement at all). Interdisciplinary scholars should have some appreciation of the disciplinary perspective (or worldview) of each discipline that they draw upon: how it sees the world and approaches research. This disciplinary perspective is instantiated in a mutually reinforcing set of theories, methods, epistemological beliefs, subjects (phenomena) addressed, and terminology. Interdisciplinary scholars also familiarize themselves with multiple works on the topic of interest so that they gain a sense of relevant debates and areas of consensus within the discipline. The interdisciplinary scholar does not simply cite works that reach congenial conclusions without placing these in context.
Interdisciplinary scholars engage in perspective-taking: They actively seek to understand why a scholar from a particular discipline might reach a particular conclusion.
An interdisciplinary scholar takes care to apply all theories and methods appropriately. Interdisciplinarity invites and encourages the use of multiple theories and methods, but not the shoddy or superficial employment of any theory or method.
Interdisciplinary scholars recognize that all theories and methods have strengths and weaknesses.
Interdisciplinary scholars respect disciplinary evaluations of research. Yet they add important avenues for interdisciplinary evaluation. They can ask to what degree the results of disciplinary research reflect disciplinary perspective, and especially the theories and methods employed within a discipline. They can also explore why researchers in different disciplines may obtain different results. Note that interdisciplinary strategies of evaluation complement disciplinary strategies.
Interdisciplinary scholars strive to integrate the best elements of disciplinary insights (those that survive both disciplinary and interdisciplinary evaluation) into a more comprehensive understanding of the question or topic under investigation.
It follows that interdisciplinary scholars do not think that disciplines are “incommensurate” (a term associated with the work of philosopher of science Thomas Kuhn’s work on paradigm changes in science). Though there are important barriers to cross-disciplinary understanding, these can be transcended well enough that scholars can draw usefully upon insights from other disciplines.
Klein, J. T., & Newell, W. H. (1998). “Advancing interdisciplinary studies” In J. G. Gaff, J. L. Ratcliff, & Associates (Eds.), Handbook of the undergraduate curriculum: A comprehensive guide to purposes, structures, practices, and change (pp. 393–415). San Francisco, CA: Jossey-Bass.
National Academies. Committee on Facilitating Interdisciplinary Research, Committee on Science, Engineering, and Public Policy (2004). Facilitating interdisciplinary research. Washington: National Academy Press. Retrieved, 21 December, 2018 from: https://www.nsf.gov/od/oia/additional_resources/interdisciplinary_research/definition.jsp
Szostak, Rick, “Extensional Definition of Interdisciplinarity” Issues in Interdisciplinary Studies.33, 94-117, 2015.