Abstract
In his pioneering Essay in Modal Logic, G. H. von Wright, after system- atising the uses of various modal words, said in a concluding note
An important use of [the modal words] is connected with the notions of an ability and of a disposition and with the verb ‘can’. For example : Jones can speak German (=it is possible for Jones to make himself understood in German) ; Jones cannot speak German (=it is impossible for Jones to make himself understood in German). We shall call the modal concepts which refer to abilities and dispositions dynamic modalities (I am indebted for the term to Mr. Geach)… The question whether the dynamic modalities, i.e. the logic of abilities and dispositions, is subject to exactly the same formal rules as the alethic modalities will have to be investigated separately. (An Essay in Modal Logic, Amsterdam, 1951, p. 54.)
The present paper was read, in various stages of development, to seminars at Stanford University, Cornell University and the Universities of Massachusetts, Lancaster and Durham. I am indebted to those who took part in those discussions, and to my fellow symposiasts at Helsinki, for much valuable criticism and stimulation. In particular I am indebted to Professors Stalnaker, Aune and Kanger and to Dr. P. J. Fitz-Patrick.
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Notes
The present paper was read, in various stages of development, to seminars at Stanford University, Cornell University and the Universities of Massachusetts, Lancaster and Durham. I am indebted to those who took part in those discussions, and to my fellow symposiasts at Helsinki, for much valuable criticism and stimulation. In particular I am indebted to Professors Stalnaker, Aune and Kanger and to Dr. P. J. Fitz-Patrick.
The line of thought explored in this first section was suggested by corresponding explorations of von Wright in the area of deontic logic. Over the years von Wright has wavered between reading a formula of deontic logic such as ‘Op’ as ‘one ought to do p’ and reading it as ‘it ought to be the case that p’. (See, for instance, ‘Deontic Logic Revisited’, Rechtstheorie 1973, p. 37). A way of reading ‘Op’ which he sometimes adopts is ‘it is obligatory to see to it that p’ (An Essay in Deontic Logic and the General Theory of Action, Amsterdam 1968, p. 37). My suggestion here is in the same spirit; but I prefer the expression ‘bring it about that p’ because ‘bring it about that’ does not carry the suggestion of intentionality, of purposively bringing it about that p, which to my ear’ see to it that p’ does.
Here I am indebted to Dr. P. J. FitzPatrick.
“He can speak Spanish or Portuguese” as Prof. A. Brod has pointed out to me, may mean “Either he can speak Spanish, or he can speak Portuguese; I don’t know which”.
For the distinctions used in the table, see F. R. Palmer, A Linguistic Study of the English Verb (London 1965); B. Aune, article ‘Can’ in The Encyclopedia of Philosophy; J. L. Austin, ‘Ifs and Cans’ in Philosophical Papers (Oxford 1961); P. Nowell-Smith, ‘Ifs and Cans’, Theoria 26 (1960) 85-101; M. R. Ayers, The Refutation of Determinism (London 1968); R. Gibbs, ‘Real Possibility’, American Philosophical Quarterly 7(1970) 340-348; A. M. Honoré, ‘Can and Can’t’, Mind 73 (1964) 463-479; J. P. Snyder, Modal Logic and Its Applications (New York 1971) and G. H. von Wright, An Essay on Modal Logic (Amsterdam 1951).
The qualification ‘current’ is important: clearly one can be constrained by past desires whose effects may now be unalterable.
These are both technical terms of von Wright’s theory, defined in such a way as to approximate to an idealisation of the intuitive meaning of the terms.
Von Wright maintains basically the same position in Explanation and Understanding (London 1971).
For instance, it might be that a satisfactory analysis of the notion of bringing about would show that if A brings it about that p then A brings it about that A brings it about that p. If so, then the second possibility would be ruled out (for an agent who brings about a state of affairs a fortiori renders it unavoidable).
‘An Analysis of Relativised Modalities’ in Philosophical Logic, ed. by J. W. Davis, D. J. Hockney, and W. K. Wilson, (Dordrecht 1969), p. 181.
For some ingenious but inconclusive arguments to the contrary, see Honoré art. cit.
For this important point I am indebted to Prof. Stalnaker.
To deal with these matters adequately would need a whole logic of action; but I think it can be seen that no combination of the system M with an action-operator will serve the purpose. For if the notion of agency represented by ‘D’ is taken to be mere brute agency, with no suggestion of intentionality or voluntariness, then CMADpDq-AMDpMDq will be a logical truth, but it will be possible to find counterexamples to CDpMDp and thus to CpMp; whereas if the notion of agency represented by ‘D’ includes a type of intentionality strong enough to safeguards CDpMDp from falsification, then it will be possible to find counterexamples to CMADpDqAMDpMDq and thus to CMpqAMpMq.
The fourth axiom appears to be misprinted in the Rechtstheorie article. As stated above it conforms to von Wright’s explanation in the accompanying English text, rather than to his formulation (in Russellian style) of the axioms.
At least to some versions of this principle; Aristotle does not appear consistent in its enunciation.
If we put ‘T’ for ‘try to bring about that’ then a first attempt at the conditional analysis of ‘can’ replaces ‘Mp’ by ‘CTpp’. Then the law to which we have found counter examples is CCTApqApqCAppCTqq which is not a distribution law. ‘T’ does not in fact distribute over disjunction (ETApqATpTq is not a law); but in a logic of rational attempts, ETKpqKTpTq would no doubt be a law so that ‘T’ would distribute over conjunction. The trouble with ‘CTpp’ for ‘Mp’ is that one becomes omnipotent by never trying.
In Essays on Freedom of Action, ed. by T. Honderich (London 1973).
It is a merit of von Wright’sRechtstheorie system that it enables one to distinguish between CpMDq and MDCpq.
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© 1976 D. Reidel Publishing Company, Dordrecht-Holland
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Kenny, A. (1976). Human Abilities and Dynamic Modalities. In: Manninen, J., Tuomela, R. (eds) Essays on Explanation and Understanding. Synthese Library, vol 72. Springer, Dordrecht. https://doi.org/10.1007/978-94-010-1823-4_11
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