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Obligation and Ability

Published online by Cambridge University Press:  09 June 2010

R. N. McLaughlin
R. N. McLaughlin
Affiliation:
Don Mills, Ontario
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Extract

The Robbers' Paradox has provided a focus of discussion in some of the recent articles on deontic logic. The paradox affects those systems which recognize in some way the maxim ‘Ought entails can’ and stems from a law, derivable in these systems, which can be put into words in this way:

(i) If doing a necessitates my doing b, then if doing b is forbidden, doing a is forbidden.

Type
Articles
Information
Dialogue: Canadian Philosophical Review / Revue canadienne de philosophie , Volume 4 , Issue 3 , December 1965 , pp. 323 - 335
Copyright
Copyright © Canadian Philosophical Association 1965

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References

1 The Robbers' Paradox is a variant of the Paradox of the Good Samaritan which was first brought forward, I believe, by. A. N. Prior in “Escapism: The Logical Basis of Ethics” in Essays in Moral Philosophy, ed. Melden, A.I., pp. 135–146.Google Scholar The latter paradox has been substantially overcome. See Nowell-Smith, P.H. and Lemmon, E.J., Mind, vol. Lxix, pp. 289–300CrossRefGoogle Scholar.

2 Nowell-Smith and Lemmon (ibid.) replace (1) by a somewhat different law and show that the paradox does not arise from it. Nozick, Robert and Routley, Richard, Mind, vol. Lxxi, pp. 377–382, also pursue a technique of avoidanceCrossRefGoogle Scholar.

3 For ease of recognition, references to acts in the body of the text are italicized. The convention is dropped for purely symbolic formulations.

4 The ‘specific’ sense of ‘able’ is comparable to Nowell-Smith's notion of ‘fully able’ and Austin's ‘all in’ sense of ‘can’. See, Nowell-Smith, P.H., “Ifs and Cans”, Theoria, (1960), pp. 85–101Google Scholar, and Austin's, J. L. essay of the same title printed in his Philosophical Papers, pp. 153–180Google Scholar. The view that ‘ought’ entails ‘can’ in its generic sense only has been put by von Wright, G. H. in Norm and Action, pp. 111–112Google Scholar.

5 The word ‘presupposition’ was used in this way by Remnant, Peter in “Professor Rynin on the Autonomy of Morals”, Mind, vol. LXVIII, at p. 253. Remnant attributed the suggestion to D.G. Brown. He did not say whether the ability presupposed was to be specific or genericGoogle Scholar.

6 Discussions of this proof procedure in reference to the monadic predicate calculus are contained in several standard texts. See W. and M. Kneale, The Development of Logic, p. 726, and H. Leblanc, An Introduction to Deductive Logic, pp. 218–220.

7 See A.N. Prior's discussion of this system, and of the objections to it, in his Formal Logic, Second Edition, pp. 226–227.

8 See his discussion of this problem, op. cit., pp. 224–225, and also his “The Paradoxes of Derived Obligation”, Mind, Vol. LXIII, p. 64; and see Wright's, G.H. von “Deontic Logic and Derived Obligation”, Mind, Vol. LXV, p. 507, and Norm and Action, pp. 187–188. The argument in my own “Further Problems of Derived Obligation”, Mind, Vol. LXIV, p. 400, suffers from my failure to distinguish between what the actor does and what he can doGoogle Scholar.