That is, it is possibly true. Basically, Plantinga argues that ordinary objects such as persons cannot be constituents of propositions because the propositions can exist without the individual's existing. There are different replies to Plantinga's argument one can make depending on the metaphysical position one takes with respect to modality. So Socrates can be a constituent of a proposition even in circumstances where Socrates is not an actual object. John can describe or represent a circumstance or world where John does not exist.
Ordinary individuals change over time including coming into and going out of existence.
No human person exists without being a certain age. Again the reply that one makes to the temporal modal objection is like the reply that one makes to the alethic modal objection in that it depends on one's metaphysical views concerning time and individuals. The object that is a constituent of a proposition is a complete object in that all the temporal stages or parts of the object in question are involved. So part of Socrates is 21 and part is 37. On the other hand, if one holds to a 3D view where the object is wholly present at each time that it exists, then matters become a bit more complex.