It’s not hard to see why Chisholm finds this example perplexing. For we have arrived at a world at which the table that is identified as x is composed of all and only the parts that in fact compose y; and the table that is identified as y is composed of all and only the parts that in fact compose x. Is this world in fact distinct from the actual world? What possible basis is there for saying that the table composed of the x parts is y? Why isn’t that table x? It is partwise indiscernible from the actual x.