Abstract
In this discussion piece, I argue that David Lewis fails to support his claim that (relative to one context) time-travelling Tim cannot kill his Grandfather in 1921. This result, in turn, undermines Lewis’s contextualist solution to the Grandfather Paradox—i.e. conceding that Tim can and cannot kill Grandfather, but relative to different contexts in each case.
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Notes
What distinguishes the admissible facts from the inadmissible ones? Admissible facts will typically be facts about the presence or absence of contextually salient means or opportunities. Inadmissible facts will presumably be all the rest, including facts about the agent’s lack of success. One way in which the salient means and opportunities are selected is presumably the conversational context. (Perhaps this observation goes some way towards defusing Van Cleve’s crocodile objection and the threat of rampant relativity. (Van Cleve: xx).)
What is meant by ‘compossible’ and ‘incompossible’? Lewis does not say explicitly, but commentators have assumed that he meant logical compatibility and incompatibility. However, this reading creates problems for Lewis’s own Finnish example. My speaking Finnish is not logically incompatible with my never having learnt to speak Finnish; nor is the structure of an ape’s larynx and central nervous system logically incompatible with its speaking Finnish. (I pointed this out in Garrett 2016: 248, n.3; Van Cleve also picks up on it (Van Cleve: xx).) Perhaps Lewis’s analysis can be revised to avoid these difficulties.
It is troubling to attribute an obviously fallacious inference to one of the world’s greatest modal logicians. Troubling also to suggest that his reasoning has fatalist elements. Lewis, after all, takes pains to advertise his anti-fatalist credentials by criticising a particularly egregious piece of fatalist trickery (Lewis 1976: 151–2). Nonetheless, I do not think that anything I have said distorts or misinterprets Lewis’s line of argument. Fortunately, the point I make in the last paragraph of the text may go some way towards rehabilitating Lewis’s reasoning.
I am grateful to a referee from this journal, Daniel Stoljar, Alan Hajek and JJ Joaquin of Manila.
References
Garrett, B. (2016). Tim, Tom, time and fate: Lewis on time travel. Analytic Philosophy., 57(3), 247–252.
Lewis, D. (1976). The paradoxes of time travel. American Philosophical Quarterly, 13(1), 145–152.
Russell, B. (1913). On the notion of cause. Proceedings of the Aristotelian Society, 13(1), 1–26.
Taylor, R. (1962). Fatalism. The Philosophical Review, 71, 56–66.
Van Cleve, J. (2019). Lewis and Taylor as partners in sin. Acta Analytica, 1–11.
Vihvelin, K. (1996). What time travelers cannot do. Philosophical Studies, 81, 315–330.
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Garrett, B. Bulletproof Grandfathers, David Lewis, and ‘Can’t’-Judgements. Acta Anal 34, 177–180 (2019). https://doi.org/10.1007/s12136-019-00387-z
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DOI: https://doi.org/10.1007/s12136-019-00387-z