Joseph Y. Halpern
Joseph Y. Halpern researched reasoning about knowledge, uncertainty and causality. He earned his Harvard mathematics doctorate in 1981, joined IBM Research in 1982 and became a Cornell professor in 1996. With Yoram Moses he studied common knowledge in distributed systems; with Ronald Fagin, Moses and Moshe Y. Vardi he co-authored Reasoning About Knowledge in 1995. His uncertainty book appeared in 2003. An AAAI Fellow from 1993, he chaired Cornell’s computer-science department from 2010 to 2014. He died in February 2026.
- Works
- 779
- Citations
- 36,401
- h-index
- 81
Publication numbers from OpenAlex, as of 14 October 2026.
Timeline
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1981–1982
Mathematics and IBM research
Halpern earned his Harvard mathematics doctorate in June 1981. He held a joint Harvard–MIT postdoctoral appointment before joining IBM Research in August 1982.
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1990–1995
Knowledge and common knowledge
Halpern and Yoram Moses published Knowledge and Common Knowledge in a Distributed Environment in 1990. He also coauthored the 1995 Reasoning About Knowledge book with Ronald Fagin, Moses and Moshe Y. Vardi.
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1993–1996
Recognition and Cornell
AAAI elected Halpern a Fellow in 1993. He became a Cornell professor in August 1996 after IBM Research.
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2003–2014
Uncertainty and academic leadership
Halpern published Reasoning About Uncertainty in 2003, with a second edition in 2017. He chaired Cornell’s computer-science department from August 2010 to June 2014. His scholarship and teaching linked reasoning, computer science and decision theory.
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2026
A completed historical career
Halpern died on 13 February 2026. His research covered knowledge, uncertainty, causality and the interface of game theory with computing.
Sources and credits
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