Fitch and Mary


There is a rather famous “Fitch argument” that not everything that is true is knowable. There is a rather famous “Mary argument” that is often used to argue that reductive physicalism is false. This paper sets out the two side by side as the Fitch Knowability Paradox and the Mary Knowability Paradox. It is found that they have the same logical form and thus the question of validity can be evaluated with the same tools. Likening the two is useful, since it avoids the problem that since the logical forms involved in intentional and experiential contexts are unknown, we cannot be in a position to evaluate whether the Mary is deductively valid without begging questions.

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  1. 1.

    Churchland writes this as K (f)mx.

  2. 2.

    See Fitch (1963).

  3. 3.

    It is briefly mentioned in Kvanvig (2006).


  1. Churchland P (2004) “Knowing Qualia: A Reply to Jackson (with Postscript 1997)” in Peter Ludlow, Yujiri Nagasawa, Daniel Stoljar (2004), pp 163–178. First published in “A Reply to Jackson,” in A Neuro-computational Perspective (The MIT Press, Cambridge, 1989), pp 67–76; and as “Postscript” in Churchland PM, Churchland PS, On the Contrary: Critical essays 1987–1997 (The MIT Press, Cambridge, 1997)

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  5. Ludlow P, Nagasawa Y, Stoljar D (eds) (2004) There is something about mary: essays on phenomenal consciousness and Frank Jackson’s knowledge argument. MIT Press, Cambridge

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Correspondence to Gregory Landini.

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Landini, G. Fitch and Mary. Axiomathes 30, 193–199 (2020).

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  • Qualia
  • Jackson
  • Physicalism
  • Churchland