COWLES FOUNDATION FOR RESEARCH IN ECONOMICS
AT YALE UNIVERSITY

Box 208281
New Haven, CT 06520-8281

COWLES FOUNDATION DISCUSSION PAPER NO. 1062

"Common Knowledge"

John Geanakoplos

August 1993

This paper surveys the implications of "common knowledge" in interactive epistemology and game theory, with special emphasis on speculation, betting, agreeing to disagree, and coordination. The implications of approximate common knowledge are also analyzed. Approximate common knowledge is defined three ways: as knowledge of knowledge ... of knowledge, iterated N times; as p-common knowledge; and as weak p-common knowledge. Finally the implications of common knowledge are examined when agents are boundedly rational.