Paul Richard Thagard (; born 1950) is a Canadian philosopher who specializes in cognitive science, philosophy of mind, and the philosophy of science and medicine. Thagard is a professor emeritus of philosophy at the University of Waterloo. He is a writer, and has contributed to research in analogy and creativity, inference, cognition in the history of science, and the role of emotion in cognition. In the philosophy of science, Thagard is cited for his work on the use of computational models in explaining conceptual revolutions; his most distinctive contribution to the field is the concept of explanatory coherence, which he has applied to historical cases. He is heavily influenced by pragmatists like C. S. Peirce, and has contributed to the refinement of the idea of inference to the best explanation. In the philosophy of mind, he is known for his attempts to apply connectionist models of coherence to theories of human thought and action. He is also known for HOTCO ("hot coherence"), which was his attempt to create a computer model of cognition that incorporated emotions at a fundamental level. In his general approach to philosophy, Thagard is sharply critical of analytic philosophy for being overly dependent upon intuitions as a source of evidence.
Biography Thagard was born in Yorkton, Saskatchewan on September 28, 1950. He is a graduate of the Universities of Saskatchewan (B.A. in philosophy, 1971), Cambridge (M.A. in philosophy, 1973), Toronto (Ph.D. in philosophy, 1977) and Michigan (M.S. in computer science, 1985). He was Chair of the Governing Board of the Cognitive Science Society [1], 1998–1999, and President of the Society for Machines and Mentality [2], 1997–1998. In 2013 he won a Canada Council Killam Prize, and in 1999 was elected a fellow of the Royal Society of Canada. In 2003, he received a University of Waterloo Award for Excellence in Research, and in 2005 he was named a University Research Chair. Thagard was married to the psychologist Ziva Kunda. Kunda died in 2004.
Philosophical work
Explanatory coherence Thagard has proposed that many cognitive functions—including perception, analogy, explanation, decision-making, and planning—can be modeled as coherence-based constraint satisfaction processes rather than as purely deductive or probabilistic reasoning. Thagard (together with Karsten Verbeurgt) put forth a formalization of coherence as a constraint satisfaction problem. In this model, coherence operates over a set of representational elements (such as propositions or images) that may either fit together (cohere) or resist fitting together (incohere). Pairs of elements are linked by either positive or negative constraints. If two elements p {\displaystyle p} and q {\displaystyle q} cohere, they are connected by a positive constraint ( p , q ) ∈ C + {\displaystyle (p,q)\in C^{+}} ; if they incohere, they are connected by a negative constraint ( p , q ) ∈ C − {\displaystyle (p,q)\in C^{-}} . Constraints are weighted, such that for each constraint ( p , q ) ∈ C + ∪ C − {\displaystyle (p,q)\in C^{+}\cup C^{-}} there is an associated positive weight w ( p , q ) {\displaystyle w(p,q)} . According to Thagard, coherence maximization involves partitioning elements into accepted ( A {\displaystyle A} ) and rejected ( R {\displaystyle R} ) sets so as to satisfy the maximum number, or maximum total weight, of constraints. A positive constraint ( p , q ) {\displaystyle (p,q)} is satisfied if both elements are accepted ( p , q ∈ A {\displaystyle p,q\in A} ) or both rejected ( p , q ∈ R {\displaystyle p,q\in R} ). A negative constraint ( p , q ) {\displaystyle (p,q)} is satisfied if one element is accepted and the other rejected (for example, p ∈ A {\displaystyle p\in A} and q ∈ R {\displaystyle q\in R} ). This formulation treats reasoning as a global optimization process over interconnected representations rather than as a sequence of local logical inferences.
Philosophy of science Thagard worked on the demarcation problem in philosophy of science. Faced with the failure of verifiability and falsifiability, what he called "post positivist depression", he proposed in 1978 a criterion to define pseudoscience, with the broader goal being rescuing science from the relativism of Feyerabend and Rorty. According to Thagard's criterion, "A theory which purports to be scientific is pseudoscientific if and only if": It has been less progressive than alternative theories over a long period of time, and faces many unsolved problems; but The community of practitioners makes little attempt to develop the theory towards solutions of the problems, shows no concern for attempts to evaluate the theory in relation to others, and is selective in considering confirmations and disconfirmations.
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