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 , 1998-1999, and President of the Society for Machines and Mentality , 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