Paul Richard Thagard FRSC (/ˈθeɪɡɑːrd/; 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;^[4] his most distinctive contribution to the field is the concept of explanatory coherence, which he has applied to historical cases.^[5][6][7] 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.^[8]

In the philosophy of mind, he is known for his attempts to apply connectionist models of coherence to theories of human thought and action.^[9] 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.^[10]

In his general approach to philosophy, Thagard is sharply critical of analytic philosophy for being overly dependent upon intuitions as a source of evidence.^[1]

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 [2], 1998–1999, and President of the Society for Machines and Mentality [3], 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.

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.^[11][12] 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 , and if two elements and incohere they are connected by a negative constraint . Furthermore, constraints are weighted, i.e., for each constraint there is a positive weight .

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

Thagard worked on the demarcation problem in philosophy of science. Faced with the failure of verifiability and falsifiability, what he called "post positivist depression",^[13]: 114 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":

1. It has been less progressive than alternative theories over a long period of time, and faces many unsolved problems; but
2. 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.^[14][15]

However, in 1988, Thagard wrote that this proposal should "be abandoned," because it had two flaws. Firstly it was hopeless to attempt to find necessary and sufficient conditions for pseudoscience in general, and secondly, the criterion was too soft on astrology which it was specifically meant to brand as pseudoscience.^[13]: 168 Nonetheless, Thagard, didn't completely abandon his criterion, but instead incorporated it into his new solution to the demarcation problem, which he called "Profile of Science and Pseudoscience", a collection of psychological, historical and logical characteristics, against which a discipline could be compared and categorized as either science or pseudoscience. This process, though not "strict necessary or sufficient", could fulfill the normative goals of science, or what Thagard prefers to call "Natural philosophy", by relying "on descriptions of how everyday and scientific reasoning actually works."^[13]: 114

^[13]: 170

He describes the Aristotelian realist philosophy of mathematics as "the current philosophy of mathematics that fits best with what is known about minds and science."^[16]

Thagard is the author/co-author of 15 books and over 200 articles.

• Balance: How it Works and What it Means. (Columbia University Press, 2022).
• Bots and Beasts: What Make Machines, Animals, and People Smart? (MIT Press, 2021).
• Brain-Mind: From Neurons to Consciousness and Creativity. (Oxford University Press, 2019).
• Mind-Society: From Brains to Social Sciences and Professions. (Oxford University Press, 2019).
• Thagard, Paul (2019). Natural Philosophy: From Social Brains to Knowledge, Reality, Morality, and Beauty. New York: Oxford University Press. ISBN 9780190686444.
• The Cognitive Science of Science: Explanation, Discovery, and Conceptual Change. (MIT Press, 2012).
• The Brain and the Meaning of Life Princeton University Press, 2010 ISBN 978-1-4008-3461-7
• Hot Thought: Mechanisms and Applications of Emotional Cognition (MIT Press, August, 2006, ISBN 0-262-20164-X)
• Coherence in Thought and Action (MIT Press, 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 978-84-96859-21-0)
• Conceptual Revolutions (Princeton University Press, 1992, ISBN 0-691-02490-1)
• Computational Philosophy of Science (MIT Press, 1988, Bradford Books, 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, Bradford Books, 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).

• List of University of Waterloo people
• Computational-representational understanding of mind

• Thagard's website.
• Thagard's blog at Psychology Today