Paul R. Thagard

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Paul Thagard is Professor of Philosophy, with cross appointment to Psychology and Computer Science, and Director of the Cognitive Science Program, at the University of Waterloo. He is a graduate of the Universities of Saskatchewan, Cambridge, Toronto (Ph.D. in philosophy, 1977) and Michigan (M.S. in computer science, 1985). He is the author of:

Hot Thought: Mechanisms and Applications of Emotional Cognition (MIT Press, August, 2006, ISBN 0-262-20164-X)
Coherence in Thought and Action (Bradford Book, 2000, ISBN 0-262-20131-3)
How Scientists Explain Disease (Princeton University Press, 1999, ISBN 0-691-00261-4)
Mind: An Introduction to Cognitive Science (MIT Press, 1996; second edition, 2005, ISBN 0-262-20154-2)
Conceptual Revolutions (Princeton University Press, 1992, ISBN 0-691-02490-1)
Computational Philosophy of Science (MIT Press, 1988, Bardford Book, 1993, ISBN 0-262-70048-4)

And co-author of:

Mental Leaps: Analogy in Creative Thought (MIT Press, 1995, ISBN 0-262-08233-0)
Induction: Processes of Inference, Learning, and Discovery (MIT Press, 1986, Bardford Book, 1989, ISBN 0-262-58096-9)

He is also editor of:

Philosophy of Psychology and Cognitive Science (North-Holland, 2006, ISBN 0-444-51540-2).

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. He has held a Canada Council Killam fellowship, 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.

[edit] Coherence

Paul Thagard has proposed that many cognitive functions, including perception, analogy, explanation, decision-making, planning etc., can be understood as a form of (maximum) coherence computation.

Thagard (together with Karsten Verbeurgt) put forth a particular formalization of the concept of coherence as a constraint satisfaction problem. The model posits that coherence operates over a set of representational elements (e.g., propositions, images, etc.) which can either fit together (cohere) or resist fitting together (incohere).

If two elements p and q cohere they are connected by a positive constraint $(p,q) \in C^+$ , and if two elements $p$ and $q$ incohere they are connected by a negative constraint $(p,q) \in C^-$ . Furthermore, constraints are weighted, i.e., for each constraint $(p,q) \in C^+ \cup C^-$ there is a positive weight $w (p, q)$ .

According to Thagard, coherence maximization involves the partitioning of elements into accepted ( $A$ ) and rejected ( $R$ ) elements in such a way that maximum number (or maximum weight) of constraints is satisfied. Here a positive constraint $(p, q)$ is said to be satisfied if either both $p$ and $q$ are accepted ( $p, q \in A$ ) or both $p$ and $q$ are rejected ( $p, q \in R$ ). A negative constraint $(p, q)$ is satisfied if one element is accepted(say $p \in A$ ), and the other rejected ( $q \in R$ ).