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  • Junior Fellow Harvard University 1956–1959
  • Professor Helsinki University 1959–1970
  • Stanford University 1964–1982,
  • Florida State University 1978–1990,
  • Boston University 1990
  • Research Professor at the Academy of Finland 1970–1981
  • John Lock Lecturer, Oxford University 1964
  • Axel Hägerström Lecturer, Uppsala University 1983
  • Immanuel Kant Lecturer, Stanford University 1984
  • Chaim Perelman Lecturer, TelAviv University 1994
  • President of International Union of History and Philosophy of Science 1975
  • President of American Philosophical Association, Pacific Division 1975–1976
  • Vice President of International Federation of Philosophical Societies 1993–1998
  • President of Institut International de Philosophie 1999–2002
  • Honorary Member of Finnish Academy of Science and Letters,
  • Societas Scientiarum Fennica Institut International de Philosophie,
  • American Academy of Arts and Sciences, Norwegian Academy of Science and Letters,
  • Foreign Member of Russian Academy of Science, Hungarian Academy of Science
  • Awarded Honorary Doctorate by Liège University 1984, Jagiellonian University 1995, Uppsala University 2000, University of Oulu 2002 and University of Turku 2003