 The core of Plantinga’s answer to the possibilist challenge is the notion of an (individual) essence, an idea that traces back clearly at least to  Boethius.[67]  Plantinga defines the  essential properties  of an object to be those properties that it couldn’t possibly have lacked without simply failing to exist  altogether.[68]  A bit more formally put: \(P\) is essential to \(a\) just in case, necessarily, if \(a\) exists (i.e., for an actualist like Plantinga, if something is identical to \(a\)), then \(a\) has \(P\). Intuitively, the essential properties of an object are the ones that make the object “what it is”. For example, on at least some conceptions of human persons, being human is essential to Bergoglio while being Catholic isn’t—there is (on these conceptions) no possible world containing Bergoglio in which he fails to be human but many in which he, say, becomes a Buddhist monk or is a lifelong atheist. A property is an essence of an object \(a,\) then, just in case (i) it is essential to \(a\) and (ii) nothing but \(a\) could have exemplified it; and a property is an essence simpliciter just in case it is possibly an essence of something.