Ted Sider aptly and concisely states the self-visitation paradox thus: 'Suppose I travel back in time and stand in a room with my sitting 10-year-old self. I seem to be both sitting and standing, but how can that be?' (2001, 101). I will explore a relativist resolution of this paradox offered by, or on behalf of, endurantists.1 It maintains that the sitting [End Page 359] and the standing are relative to the personal time or proper time of the time traveler and is intended to yield the result that Ted is sitting at a certain initial personal/proper time but is not standing relative to that time. Similarly, it is also supposed to yield that Ted is standing relative to a later personal/proper time, but not sitting relative to that time. Such a traveler-time relativism has been offered by Paul Horwich (1975, 433-5; 1987, 114-15) and also by Simon Keller and Michael Nelson (2001, 344). I will show that this relativist approach is a non-starter. It is so because Ted is sitting and standing at both the initial and the later personal/ proper time. Though I will do my best to recapture what these authors found appealing in traveler-time relativism, I will conclude by suggesting that endurantists resist all relativist resolutions and instead recognize that sitting and standing are compatible properties.
II Traveler-Time Relativism
For relativists, Ted's sitting is somehow relative, and so is his standing. So, for example, spatial-location relativism holds that Ted is sitting at some place, say, here, though it is not the case that he is standing here. While Ted is standing somewhere else, say, there, it is not the case that he is sitting there. He can be sitting here and standing there so long as he is not also standing here and sitting there. What is impossible is for the person to be simultaneously sitting and standing in one location. Kristie Miller (2006, see especially 315-16) defends a variation of this approach that makes the sitting and standing relative to a space-time region. The primary attraction of spatial-location relativism or any plausible relativism is that it thwarts a threat to endurantism from Leibniz's Law by undermining the thought that the sitter and the stander differ on their properties. Relativizing to time, a familiar endurantist move in treatments of the problem of change (i.e. the problem of temporary intrinsics), is obviously of no help to the endurantist regarding self visitation. The sitting and standing take place at the same time. Being told, for instance, that Ted is standing now and sitting now does nothing to block the threat from Leibniz's Law.2 [End Page 360]
Regarding this threat, for all relativisms, it is important that the relativized property not be analyzable as a certain conjunction. For example, the spatial-location relativist should not accept that being sitting here is equivalent to the conjunction of being sitting (simpliciter) and being here. By taking the analogous position about being standing there, the relativist would still be stuck holding that Ted is sitting and Ted is standing. The relativist denies that Ted is sitting (simpliciter) and denies that he is standing (simpliciter).3
According to traveler-time relativism, sitting and standing are relative to the traveler=s personal time or proper time. Both these temporal concepts are, roughly, time as measured by the traveler=s wristwatch. Personal time is a concept introduced and defined by David Lewis (1976, 146). It is based on a numerical assignment to an ordering of the temporal stages of a person such that regularities — like that food digests and hair grows — match those that commonly hold with respect to time itself, what Lewis calls external time. Proper time is a concept employed in the theory of relativity. It is calculated using an assignment of coordinates to events along a spacetime path and is given by the spatiotemporal 'length' of that path. 'In general, the proper time measured by a clock is the time relative to the frame of reference in which...