Journal of Philosophical Logic

, Volume 32, Issue 1, pp 19–42

Mechanism, Truth, and Penrose's New Argument

  • Stewart Shapiro

DOI: 10.1023/A:1022863925321

Cite this article as:
Shapiro, S. Journal of Philosophical Logic (2003) 32: 19. doi:10.1023/A:1022863925321


Sections 3.16 and 3.23 of Roger Penrose's Shadows of the mind (Oxford, Oxford University Press, 1994) contain a subtle and intriguing new argument against mechanism, the thesis that the human mind can be accurately modeled by a Turing machine. The argument, based on the incompleteness theorem, is designed to meet standard objections to the original Lucas–Penrose formulations. The new argument, however, seems to invoke an unrestricted truth predicate (and an unrestricted knowability predicate). If so, its premises are inconsistent. The usual ways of restricting the predicates either invalidate Penrose's reasoning or require presuppositions that the mechanist can reject.

incompleteness Lucas mechanism Penrose truth 

Copyright information

© Kluwer Academic Publishers 2003

Authors and Affiliations

  • Stewart Shapiro
    • 1
    • 2
  1. 1.Ohio State UniversityColumbusUSA
  2. 2.University of St. AndrewsSt. AndrewsScotland

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