I am a philosopher with an extensive interest and background in natural science. I have a B.A. in mathematics from the University of California (Santa Barbara) and a Ph.D. in philosophy from Brown University. My current position is Full Professor of Philosophy at the University of Colorado (Boulder).

Before I became a philosopher, I was a software engineer. After receiving my Ph.D. in philosophy, I spent a year (1985-86) on a postdoctoral fellowship in philosophy and computer science at Stanford University’s Center for the Study of Language and Information (CSLI). I am affiliated with the NASA Astrobiology Institute (NAI) and a Co-I in the Center for Astrobiology at the University of Colorado.

My research is focused in the areas of philosophy of science, philosophy of logic and metaphysics. I am particularly interested in the methodology and justification of historical science, the nature of scientific theories and the role of models in science, philosophy of biology (microbiology, astrobiology, the origins of life, the nature of life, and the possibility of a 'shadow biosphere', a term which I coined), and the nature of causation (including issues about mechanism and emergence).

I enjoy teaching and sharing my work with others. I teach undergraduate and graduate students. I also frequently give presentations to scientists, journalists, high school classes, K-12 teachers, and to the general public.