Embodied and Distributed Aspects of Abductive Diagnostic Reasoning Lorenzo Magnani (lmagnani@unipv.it ) Department of Philosophy and Computational Philosophy Laboratory, University of Pavia, Piazza Botta 6, 27100 Pavia, Italy and Program in Philosophy, Science, and Technology, Georgia Institute of Technology, 685 Cherry Street, Atlanta, GA, 30332-0332, USA Alberto Gatti (gatti3@unisi.it ) Department of Philosophy and Social Sciences, University of Siena, Via Roma 47, 53100 Siena, Italy Abstract In this paper we introduce diagnostic reasoning through a case study which demonstrates the presence of a mixture of theoretical and extra-theoretical thinking activities. The con- cept of “theoretical” abduction is the most suitable one for modeling the process of discovery but also of selecting pre- stored hypotheses, like in the case of diagnostic reasoning. However, as an internal inferential process, theoretical abduc- tion does not capture many reasoning situations in which ac- tion plays a fundamental role. To account for those cases of “thinking through doing” in which action takes an epistemic role we propose to adopt the concept of manipulative abduc- tion. Diagnostic reasoning represents a suitable example of reasoning in which manipulative “selective” abduction plays a central role next to theoretical abduction. To illustrate the epistemic role of actions and the distribution of the cognitive and epistemic effort we can observe in some diagnostic tasks, the paper considers the case of medical semeiology and the use of external medical tools. The Abductive Epistemological Model of Diagnostic Reasoning Theoretical Abduction A hundred years ago, C. S. Peirce (CP, 1931-1958) coined the concept of abduction in order to illustrate that the proc- ess of scientific discovery is not irrational and that a logic of discovery is possible. Peirce interpreted abduction essen- tially as an “inferential” creative process of generating a new hypothesis. Abduction has a logical form, distinct from deduction and induction. Reasoning which starts from rea- sons and looks for consequences is called deduction; that which starts from consequences and looks for reasons is called abduction. Abduction is the process of inferring certain facts and/or laws and hypotheses that render some sentences plausible, that explain or discover some (eventually new) phenomenon or observation; it is the process of reasoning in which ex- planatory hypotheses are formed and evaluated. There are two main epistemological meanings of the word abduction (Magnani, 2001): 1) abduction that only generates “plausi- ble” hypotheses (“selective” or “creative”) and 2) abduction considered as inference “to the best explanation”, which also evaluates hypotheses. To illustrate from the field of medical knowledge, the discovery of a new disease and the manifestations it causes can be considered as the result of a creative abductive inference. Therefore, “creative” abduc- tion deals with the whole field of the growth of scientific knowledge. This is irrelevant in medical diagnosis where instead the task is to “select” from an encyclopedia of pre- stored diagnostic entities. We can call both inferences am- pliative, selective and creative, because in both cases the reasoning involved amplifies, or goes beyond, the informa- tion incorporated in the premises. Theoretical abduction 1 certainly illustrates much of what is important in creative abductive reasoning, in humans and in computational programs, but fails to account for many cases of explanations occurring in science when the exploi- tation of environment is crucial. It fails to account for those cases in which there is a kind of “discovering through do- ing”, cases in which new and still unexpressed information is codified by means of manipulations of some external ob- jects (epistemic mediators). The concept of manipulative abduction 2 captures a large part of scientists’ and physi- cians’ thinking where the role of action is central, and where the features of this action are implicit and hard to be elicited Peirce uses the terms “inference” and “inferential proc- ess” to refer to abduction. It is useful to try to clarify the meaning of the term “inference” as considered by Peirce’s thought. Peirce stated that all thinking is in signs, and signs can be icons, indices or symbols. Moreover, all inference is a form of sign activity, where the word sign includes “feel- ing, image, conception and other representation” (CP 5.283). Feelings, images, simulations, etc., are currently characterized as forms of model-based reasoning (Magnani & Nersessian, 2002). Consequently, following Peirce, we can say that a considerable part of thinking activity is model-based (cf. footnote 1), that most of the forms of con- stitution of phenomena are characterized in a model-based way. We use the term “model-based reasoning” following Nersessian (1995), that is, to indicate the construction and manipulation of various kinds of representations, not neces- sarily sentential and/or formal. Scientific concept formation, scientific discovery, and – as we will see – diagnostic rea- soning are often related to heuristic procedures that resort to mental/internal but also to external “models” and represen- tations. 1 Magnani (2001, 2002) introduces the concept of theoretical ab- duction. He maintains that there are two kinds of theoretical abduc- tion, “sentential”, related to logic and to verbal/symbolic infer- ences, and “model-based”, related to the exploitation of internal- ized models of diagrams, pictures, etc., cf. below in this paper. 2 Manipulative abduction and epistemic mediators are introduced and illustrated in Magnani (2001).