Paul R. Thagard

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 [http://www.cognitivesciencesociety.org/] , 1998-1999, and President of the Society for Machines and Mentality [http://cs.hamilton.edu/~sfmm/] , 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