A substance is a fundamental entity that exists independently and has inherent properties. It is the primary subject of ontology, providing the foundation for understanding reality.
Identity refers to the unique characteristics or properties that define a substance. It is crucial for distinguishing one substance from another and for understanding how substances persist over time.
Essentialism is the philosophical position that substances have essential properties that define their identity. This concept is central to discussions about substance identity, as it helps determine what makes a substance what it is.