 To accept SI does not immediately block swapping (Schaffer 2001: 250). For, SI (just like OI and PI) is a principle about trope individuation that holds intra-worldly. In this case: within any given world, no two exactly similar tropes are at zero distance from each other. Swapping, on the other hand, concerns what is possibly true (or not) of exactly similar tropes considered inter-worldly. But this means that, although SI does not declare swapping possible, it doesn’t rule it out either. According to the proponent of SI, this is actually a good thing. For there is one possibility that it would be unfortunate if one’s principle of individuation did block, namely the possibility—called sliding—that this red-trope here could have been there had the wind blown differently (Schaffer 2001: 251). To get the desired result (i.e., to block swapping while allowing for sliding), Schaffer suggests we combine trope theory with SI and a Lewisian counterpart theory of transworld identity (Lewis 1986). The result is an account according to which exactly resembling tropes are intra-worldly identical if they inhabit the same position in space-time. And according to which they are inter-worldly counterparts, if they are distinct, yet stand in sufficiently similar distance- and other types of relations to their respective (intra-worldly) neighbors. With this addition in place, Schaffer claims, a trope theory which individuates its posits with reference to their spatiotemporal position will make room for the possibility of sliding, because (2001: 253):