Mechanism, truth, and Penrose’s new argument

Stewart Shapiro

Research output: Contribution to journalArticlepeer-review

19 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)19-42
Number of pages24
JournalJournal of Philosophical Logic
Publication statusPublished - Feb 2003


  • incompleteness
  • Lucas
  • mechanism
  • Penrose
  • truth


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