This volume contains the symposium papers presented at the twentieth biennial meeting of the Philosophy of Science Association held in Vancouver, British Columbia, November 2–4, 2006.

If we consider also the symposia, philosophy of biology, physics, and general philosophy of science are still dominant. However, we see a shift in general philosophy of science toward more specific topics such as causality, models, experimental philosophy, and formal epistemology. General philosophy of science comprised only 20% of all accepted Contributed Papers.

Philosophy of economics and social science, evolutionary psychology, philosophy of psychology, and the decision/game theory areas are well represented, and we see a significant growth trend with respect to past PSA meetings. Philosophy of chemistry and medicine are also significantly growing.

Thanks are due to many people who made the meeting successful. Miriam Somon, PSA2006 Program Chair, generously helped with her experience and knowledge of PSA rules. George Gale, PSA Executive Secretary, coached us on procedures and deadlines and helped to plan the Presidential Reception. Jay Malone in the HSS office provided invaluable assistance for registration and local arrangements.

Brian Skyrms, PSA President 2006–2007, was active in coaching and advising us throughout the process. We thank each of you for your support and counsel. The PSA2006 Program Committee worked diligently and efficiently to select an excellent and balanced set of symposium proposals. Each proposal was refereed by at least two members of the Program Committee, and often a third referee was involved.

We thank each member of the Program Committee for their service to PSA:

Horacio Arlo-Costa (Carnegie Mellon University)

Brad Armendt (Arizona State University)

Robert Batterman (Ohio State University)

William Bechtel (University of California, San Diego)

Craig Callender (University of California, San Diego)

David Christensen (University of Vermont)

John Dupre (University of Exeter)

Branden Fitelson (University of California, Berkeley)

Patrick Grim (SUNY, Stony Brook)

Francesco Guala (University of Exeter)

Alan Hajek (Australian National University)

Hans Halvorson (Princeton University)

William Harper (University of Western Ontario)

Stephan Hartmann (Tilburg University)

Gary Hatfield (University of Pennsylvania)

Nicholas Huggett (University of Illinois at Chicago)

Kevin Kelly (Carnegie Mellon University)

Noretta Koertge (Indiana University)

Elisabeth Lloyd (Indiana University)

Penelope Maddy (University of California, Irvine)

Deborah Mayo (Virginia Tech)

Ned McClennen (Syracuse University)

Wayne Myrvold (University of Western Ontario)

John Norton (University of Pittsburgh)

Samir Okasha (University of Bristol)

David Papineau (King's College, London)

Wlodek Rabinowicz (Lund University)

Alex Rosenberg (Duke University)

Sherri Roush (University of California, Berkeley)

Sahotra Sarkar (University of Texas, Austin)

Kristin Shrader-Frechette (University of Notre Dame)

Wolfgang Spohn (University of Konstanz)

Scott Weinstein (University of Pennsylvania)

Paul Weirich (University of Missouri)

Michael Weisberg (University of Pennsylvania)

The online submissions were managed by University of Pennsylvania PPE administrative coordinator Sarah Gish-Kraus. Sarah worked quickly and efficiently, keeping in touch with authors and coordinating the co-chairs' work.

After PSA2006, Michael Dickson and his staff, Charlotte Dorlaque and Jerry Piotrowski in the office of Philosophy of Science, took over the work of collection and final preparation of the papers for publication. We thank them for the good editorial work for the PSA2006 volumes.

Finally, we thank the PSA for the opportunity to chair the PSA2006 Program Committee. It was a worthwhile, interesting experience.