  The second response involves moving from contingent properties like those involved in (2) and (3) to necessary properties, and in particular to what, following Plantinga in (1974), we will call an individual essence, which is a property that, necessarily, if x exists, then it has that property and, necessarily, only x has. The property being on David's right is not an individual essence of Paul, as Paul might have existed without having had it and Charles might have had it instead. But it is easy to turn such contingent properties into necessary ones by rigidifiying them. Paul necessarily has the property of actually being on David's right. For any world w, Paul has that rigidified property in w just in case in the actual world Paul has the (contingent) property of being on David's right. And, if Paul is the only person to have that property in the actual world, then the rigidified property is not only a necessary property of Paul but also an individual essence of Paul. Such a property “tracks” Paul across every possible world. Consider then the propositions expressed by (4) and (5).