Agency is commonly identified with freedom of choice or the possessionof unconstrained alternatives. Under irreversible time, however, thismodel is incoherent: choices that matter bind future continuation andcannot be undone without structural loss. This work reconceives agencyas the capacity to bind oneself irreversibly through commitment.Agency is thus defined not by optionality, but by binding power.Stronger agency corresponds to deeper and more stable commitments;weaker agency corresponds to shallow or easily reversible binding.Decision is distinguished from action: decision evaluates possibilities,whereas action enacts commitment by rendering alternativesirreversible in time. Degrees of agency are formalized in terms ofbinding strength and persistence. The analysis yields a structuralparadox: increasing agency reduces freedom understood as openpossibility. Agency emerges not from absence of constraint, but from thepower to impose constraint upon oneself under irreversible time.