A Defense of Focō, Ergo Volō offers a foundational resolution to the free will debate by locating agency in the act that makes all thinking possible: the direction of attention. For four centuries, philosophy has lacked an equivalent to Descartes' Cogito for the will. This book argues that such a foundation exists and is performatively undeniable: "I focus, therefore I will." The work develops a clear, non-metaphysical grounding for volition. It shows that every attempt to deny agency tacitly relies on the very capacity it seeks to refute, because attending, considering, doubting, or interpreting all presuppose volitional inflection. Agency does not appear after thought; it is already at work in structuring the conscious field in which thought becomes possible. Rather than defending libertarianism or determinism, the book reframes the debate entirely. By treating attention as the operative site of volition, it demonstrates why traditional positions have remained at an impasse and how a performative grounding resolves the stalemate without speculative metaphysics or reductive neuroscience. Written as a classical philosophical defense that is precise, restrained, and rooted in structural analysis, it engages contemporary challenges from determinism, illusionism, cognitive science, and philosophy of mind. A Defense of Focō, Ergo Volō is intended for readers interested in free will, consciousness, phenomenology, cognitive science, and the foundations of agency. It advances a simple but far-reaching thesis: volition is not something we sometimes possess; it is something we continuously enact whenever we direct our attention.