 Philosophers have thought not only about whether an object has this or that particular property essentially but also about whether an object has a special kind of essential property, an individual essence, a property that in addition to being essential to the object is also unique to it in the sense that having that property is modally sufficient for being that object (that is, it is not possible that something distinct from that object has that property). A trivial example of an individual essence is a haecceity or thisness of an object, the property of being (identical to) that very object. Some have defended the claim that there are substantive examples of individual essences. Leibniz famously held that there are, and that they can be given by purely qualitative (general) properties. Forbes (1985) also holds that there are substantive individual essences, but he disagrees with Leibniz that they can be given by purely qualitative properties. Instead, he thinks, an individual essence involves non-purely qualitative (singular) properties: for example, Socrates’s essence involves originating from the particular sperm and egg from which he actually originated. For more on modal sufficiency principles, see the