Substance Theory is a philosophical concept that posits that objects are made up of substances, which are the fundamental entities that exist independently. According to this theory, substances have properties and can undergo changes while still retaining their identity. For example, a tree remains a tree even if it loses its leaves or changes color with the seasons. In Substance Theory, substances are often contrasted with properties or qualities, which are seen as dependent on substances for their existence. This theory is significant in discussions about the nature of reality and identity, influencing various fields such as metaphysics and ontology.