“Answering the Question ‘What is life?'” (invited). AAAS, Feb 18, 2006.

“Epistemic and methodological differences between historical science and classic experimental science” (invited). Center for the History and Philosophy of Science, University of Minnesota, October 21, 2005.

“What is life?” ISHPSSB Bi-Annual Meeting, Guelph, Canada, July 16, 2005. 

“Answering the Question ‘What is life?'” (invited). Harvard University, Center for Astrobiology and the Origin of Life, May 23, 2005.

“Searching for a General Theory of Living Systems” (invited presenter). Dibner Seminar in the History and Philosophy of Biology, MBL, Woods Hole, MA, May 20, 2005.

“Defining ‘Life'” (invited). Pacific Division Meeting of the American Philosophical Association, March 25, 2005.

“Why it is a mistake to define ‘life'” (invited). ALIFE9 (Ninth Conference on Artificial Life), Boston, MA, Sept. 12, 2004.

“The Advent of Historical Science” (invited). Woodfest (The New Astronomy: Opening the Electromagnetic Window and Expanding our View of Planet Earth), University of Washington, Seattle, Washington, June 16, 2004.

“Rethinking the justification of phylogenetic methods” (invited). The A. Watson Armour III Spring Symposium: Systematics at a Crossroads Again: Biological and Philosophical Arguments in Contemporary Phylogenetics, Chicago, May 10, 2003.

“The Concept of Computability” (invited). American Mathematical Society (Special Session: “Beyond classical Boundaries of computability”), May 4, 2003.

“Defining ‘life''' (invited). Inaugural Ceremonies, Centro de Astrobiologia, Madrid, Spain, January 16, 2003.

“Historical Science, Experimental Science, and the Scientific Method” (invited). Department of Earth Resources, Colorado State University, October 7, 2002.

“Defining ‘life'” (invited). ISSOL'02 (13th International Conference on the Origin of Life). Oaxaca, Mexico, July 4, 2002. 

"What is Life?" (invited). AAAS workshop on the nature of life, Washington D.C, March 5, 2001.

“Effective Procedures and Causal Processes” (invited). Hypercomputation Workshop, London, England, May 24, 2000.

“Life in ALH84001: Confirming the Best Explanation.” NASA Astrobiology Video-Seminar, Jan. 20, 2000.

“Recipes, Algorithms, and Programs” (invited). Eastern Division Meeting of the American Philosophical Association, Dec. 28, 1999.

“Recipes, Algorithms, and Programs.” Annual Meeting of the Australasian Association of Philosophy, Melbourne (Logic Stream), Australia, July 10, 1999.

"Standards of Evidence" (invited). Mars Meteorite Symposium, University of Colorado (Boulder), August 29, 1996.

"On the Nature of Computation" (invited). Symposium on Computation, Society for Philosophy and Psychology, San Francisco State University, June 1996.

"Response to Horsten's "Can Turing Machines Bake Cakes?" (invited). Midwestern Division of the American Philosophical Association, April 29, 1995.

"The Covenience of Spatial Relations" (invited). Symposium on Symmetrical Universes, Pacific Division Meeting of the American Philosophical Association, March 30, 1995.

"The Church/Turing Thesis: Procedures, Processes and Causation" (invited). University of California (Davis), Nov. 22, 1991.

"Events and Modes of Change.” Center for the Study of Language and Information, Stanford University, April, 1986. 

"Space as an Abstract System of Non-Supervenient Relations" (invited). Symposium on Space and Time, University of California at Davis, June 6, 1985