Meta Ontology

The principle of the identity of indiscernibles holds that two individuals are the same individual if they have all the same properties. There are different forms of the principle, varying with what is allowed to count as a property. An individual has thisness if the weakest form of the principle does not apply to it. Abstract objects, places and times do not have thisness. Inanimate material objects probably do not. Animate beings, and the conscious events which involve them do have thisness, and probably other events do as well