This working paper presents the conceptual foundations of the Two-Energy Theory (TDE), a proposed research programme in fundamental physics focused on the origins of mass, the structure of time, and the nature of gravity. The document introduces the core ontological assumptions, defines key terms, and formulates structural postulates underlying the framework, while clearly distinguishing definitions, postulates, working hypotheses, and formalization requirements. Particular emphasis is placed on resonance-based mechanisms and phase-structured fields as organizing principles. No claim of experimental or observational confirmation is made. The work is intended as a conceptual framework and an invitation for further formal development, critical analysis, and independent verification. The acronym TDE originates from the Polish name “Teoria Dwóch Energii” and is retained as the established name of the framework.