  Let us now apply this thought to conscious subjects. Suppose that a given human individual had had origins different from those which he in fact had such that whether that difference affected who he was was not obvious to intuition. What would count as such a case might be a matter of controversy, but there must be one. Perhaps it is unclear whether, if there had been a counterpart to Jones’ body from the same egg but a different though genetically identical sperm from the same father, the person there embodied would have been Jones. Some philosophers might regard it as obvious that sameness of sperm is essential to the identity of a human body and to personal identity. In that case imagine a counterpart sperm in which some of the molecules in the sperm are different; would that be the same sperm? If one pursues the matter far enough there will be indeterminacy which will infect that of the resulting body. There must therefore be some difference such that neither natural language nor intuition tells us whether the difference alters the identity of the human body; a point, that is, where the question of whether we have the same body is not a matter of fact.