# Paul Thagard: Map

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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)(Trad. esp.: La mente, Buenos Aires/Madrid, Katz editores S.A, 2008, ISBN 9788496859210)
• 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 [235135], 1998-1999, and President of the Society for Machines and Mentality [235136], 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.

## 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).

## References

• Thagard, P. and Verbeurgt, K. (1998). Coherence as constraint satisfaction. Cognitive Science, 22: 1-24.

• Thagard, P. (2000). Coherence in Thought and Action. MIT Press.

Many of Thagard's coherence articles are available online at http://cogsci.uwaterloo.ca/Articles/Pages/Coherence.html

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