This text examines the philosophical and linguistic evolution of the term subject and its distinction from the concept of substrate. Starting with Aristotle's notion of hypokeimenon as an unchanging basis for change, the author traces how this assumption influenced historical scientific errors, such as the search for luminiferous ether. The development shows that energetic processes do not necessarily require a material substrate. The meaning of the term shifted from a general substance to an active agent, largely due to linguistic practices and the grammatical role of the subject as a doer of actions. Consequently, the term evolved from a passive underlying foundation into a designation for the human subject, and eventually for other living beings characterized by spontaneity and activity. The analysis follows the transition from a static metaphysical category to a dynamic understanding of subjectivity rooted in agency, offering a critical reevaluation of traditional ontological assumptions regarding the nature of existence and the process of change.