  Hudson suggests that this line of reasoning is potentially on the right track, but that the conclusion is not quite right. Parthood is a three-place relation, but the third place is not filled by a time, but by a region of space-time. To a crude approximation, x is part of y at s is true if (as we'd normally say), x is a part of y and s is a region of spacetime containing no region not occupied by y and all regions occupied by x. But this should be taken as a heuristic guide only, not as a reductive definition, since parthood is really a three-place relation, so the crude approximation does not even express a proposition according to Hudson.