This thesis investigates ambiguity as a productive architectural condition, particularly through the lens of terrain vagues: urban spaces defined by contradiction, indeterminacy, and temporal fluctuation. Based on critical philosophical frameworks, the research examines how ambiguity, often regarded as a lack of clarity, can instead become a catalyst for more sustainable spatial practices. The study begins by tracing the inherent qualities of terrain vagues and identifying their potentials. It then moves toward a design-oriented investigation, exploring how empirical analysis can abstract these qualities into operative tools. Ultimately, the paper proposes a framework for integrating ambiguity into the design process—not as an aesthetic byproduct but as a deliberate mode of engagement that challenges conventional binaries and embraces multiplicity, adaptability, and ecological sensitivity in architecture.