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What Carroll’s Tortoise Actually Proves

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Rationality requires us to have certain propositional attitudes (beliefs, intentions, etc.) given certain other attitudes that we have. Carroll’s Tortoise repeatedly shows up in this discussion. Following up on Brunero (Ethical Theory Moral Pract 8:557–569, 2005), I ask what Carroll-style considerations actually prove. This paper rejects two existing suggestions, and defends a third.

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  1. For classic statements of this thought, cf. Ryle (1950) and Thomson (1960). Main subsequent commentaries include Stroud (1979) and Smiley (1995).

  2. Throughout the paper, ‘p’ and ‘q’ are schematic letters to be replaced with full declarative sentences, and ‘φ’ and ‘ψ’ are to be replaced with verbs.

  3. It may be controversial to say that we ought to believe all the consequences of the propositions we believe (even if they are obvious). Less controversial would be to conclude from (a) and (b) to: S is permitted to believe that q and prohibited from disbelieving that q. Yet, for simplicity I shall stick to the obligation formulation.

  4. Both beliefs and intentions are propositional attitudes and may have the same content. Yet, as Broome (2002: §2) points out, believing that p differs from intending that p in at least the following sense: the former attitude is one of taking it as true (or at least plausible) that p, whereas the latter attitude is one of making it true that p.

  5. Of course, complex issues attach to this wide-scope phenomenon that cannot be discussed here. For an overview, cf. Way (2010). For example, is it really rational to refuse to intend to stay home by sticking to one’s intention to publish and dropping one’s belief that publishing requires one to stay home? Also, to what extent are we psychologically free, even if entitled, to retract intentions and beliefs in the course of our reasoning?

  6. On top of this, beliefs like (c*) are demanding, and presumably no-one besides philosophers ever entertained them. If so, only philosophers would have to deal with obligations regarding one’s attitudes; which would be absurd.

  7. The number of patterns might be reduced if it can be shown that intentions reduce to a variety of beliefs. For example, suppose that my intention to publish a paper is nothing but the belief that I will publish a paper. In that case I could apply Modus Ponens Consistency instead of Means/End Consistency: (a) I believe that I will publish a paper; (b) I believe that [I will publish a paper only if I will stay home]; (z) I ought to believe that I will stay home. Surely the thesis that intentions involve, let alone reduce to, beliefs is controversial (cf. Setiya 2009: §5).

  8. For this vexed issue, cf. Broome (2005) and Kolodny (2005).

  9. Main pioneering applications of Carroll’s Tortoise to practical reasoning are Blackburn (1995) and Schueler (1995). Below I shall mainly focus on Dreier (1997, 2001) and Brunero (2005). Further works in this area include Railton (1997), Lazar (1999), Wedgwood (2005), Jollimore (2005), Engel (2005), and Schwartz (2010). Importantly, some of these concern the internal vs. external reasons for action debate, rather than the rationality debate. Nevertheless, the parallel is quite close: where the latter speak of ‘obligations’, the former speak of ‘motivating reasons’. Cf. also Sect. 4.2 below.

  10. As Brunero himself notes, this case is slightly simplistic. Arguably, one has an obligation to believe what one’s evidence supports regarding whether p only if one is going to have any opinion about whether p at all (and perhaps also only if one is not in bad evidential circumstances).

  11. Cf. “Given that Ann’s desire for e does not move Ann to do what she acknowledges is necessary to bring e about, it is entirely unclear that a further desire (here, the desire to act as (IP) requires) would be any more successful in moving her. (Jollimore 2005: 294) The rule (IP), here, is comparable to (M/R).

  12. Incidentally, I myself am quite sympathetic to this view.

  13. For an overview of IR’s instances provided in this paper, see Table 1. For further details about the logic and dialectic of infinite regress arguments, cf. Wieland (2012).


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I am grateful to: Erik Weber and the referees of the journal for extensive feedback. The author is PhD fellow of the Research Foundation Flanders.

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Correspondence to Jan Willem Wieland.

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Wieland, J.W. What Carroll’s Tortoise Actually Proves. Ethic Theory Moral Prac 16, 983–997 (2013).

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