Investigating Knowledge and Opinion

  • John CorcoranEmail author
  • Idris Samawi Hamid
Part of the Studies in Universal Logic book series (SUL)


This work treats correlative concepts of knowledge and opinion, in various senses. In all senses of ‘knowledge’ and ‘opinion’, a belief known to be true is knowledge; a belief not known to be true is opinion. In this sense of ‘belief’, a belief is a proposition thought to be true—perhaps, but not necessarily, known to be true. All knowledge is truth. Some but not all opinion is truth. Every proposition known to be true is believed to be true. Some but not every proposition believed to be true is known to be true. Our focus is thus on propositional belief (“belief-that”): the combination of propositional knowledge (“knowledge-that”) and propositional opinion (“opinion-that”). Each of a person’s beliefs, whether knowledge or opinion, is the end result of a particular thought process that continued during a particular time interval and ended at a particular time with a conclusive act—a judgment that something is the case. This work is mainly about beliefs in substantive informative propositions—not empty tautologies.

We also treat objectual knowledge (knowledge of objects in the broadest sense, or “knowledge-of”), operational knowledge (abilities and skills, “knowledge-how-to”, or “know-how”), and expert knowledge (expertise). Most points made in this work have been made by previous writers, but, to the best of our knowledge, they have never before been collected into a coherent work accessible to a wide audience.


Belief Knowledge/opinion Propositional Operational Objectual Cognition 

Mathematics Subject Classification

03B42 03A05 



We would like to thank those who have made important contributions to the dialogue leading up to this work. Robert Barnes, Leigh Duffy, John Glanville (1921–2010), Carol Gould, Forest Hansen, Peter Hare (1935–2008), Amanda Hicks, Daniel Merrill, Joaquin Miller, Hassan Masoud, Paul Moser, Mary Mulhern, Carlo Penco, Anthony Preus, José Miguel Sagüillo, Michael Scanlan, John Shook, Andrew Spear, Yevgeny Yarmolinets, Joseph Zeccardi, and John Zeis all deserve credit. Many thanks also to all who participated in the crafting of this article, especially David Brewer, Joseph Corcoran, David Hitchcock, Leonard Jacuzzo, Timothy Madigan, James McNabb, Kristo Miettinen, Frango Nabrasa, Sriram Nambiar, Daniel Novotny, Charles Pailthorp, Paul Penner, David Plache, and Roberto Torretti. David Hitchcock and Daniel Novotny deserve special thanks for alerting us to errors and obscurities in the penultimate draft; they are almost co-authors even though they disagree with some of our conclusions.

Many of the scholars mentioned disagree with some, many, or most of the conclusions of this work. We should also acknowledge many previous writers to whom we are indebted for most of the points made in this work. Our main contribution was to have collected their thoughts into a coherent work accessible to a wide audience. This paper is a substantial reworking of “An Essay on Knowledge and Belief” [15]. The word ‘essay’ in its title was carefully chosen: the essay has no footnotes or references and it is much shorter than this investigation. The essay was inspired by responses to early drafts of the encyclopedia article “Knowledge and Belief” [17].27


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Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  1. 1.PhilosophyUniversity at BuffaloBuffaloUSA
  2. 2.PhilosophyColorado State UniversityFort CollinsUSA

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