Contingents are conceptually dyads of existence (the fact that they are) and essence (bundles of properties that define what they are, Mulla Sadra 2001-5, I: 289-92).
However, for understanding spatial transparency and mystery, the available models mostly provide only indirect indicators of the essence of these properties.
So far it has been assumed that (non-trivial) necessary and sufficient conditions for transworld identity with a given object would involve the possession, by that object, of an individual essence: a set of properties that it carries with it in every possible world in which it exists.
Treating a definition as a linguistic item, we can say that the definition specifies or picks out the essence (ousia) of the property, and a definitional statement predicates the essence of the property whose essence it is.
The property being necessarily exemplified is contained in the essence of this property.
This intuition can be served by saying that the essence of a property is constituted by its theoretical roles.
If, right at the beginning of the inquiry, we see that we use the word "beautiful" as an adjective, we may well very shortly find ourselves asking what is the essence of the property beauty that this particular example exhibits.
The categoricalist, who typically invokes quidditism which asserts that the essence of a property is given independently of its theoretical roles, seems to be under pressure to hold that this world should be distinguished from the actual world.
Edwards' model is not a whole and its parts, or a substance (a bearer of properties) and its properties, or an essence and its accidents, but agent causality.
The authors are grateful for support from the Swiss FNS (research projects on "The Theory of Essence", "Properties and Relations").
