<p>Contemporary social life is increasingly organized around projected futures that remain uncertain and contested. These futures shape present action even when shared belief or reliable prediction is absent. Existing approaches to risk, imagination, and anticipation recognize this future-oriented dimension of social life. Yet they do not fully explain how possible futures become actionable before they stabilize as beliefs, scenarios, forecasts, images, or institutionalized expectations. This article addresses that gap by introducing anticipatory supposition within the framework of Homo Putans: the human being as a supposing being. It argues that actors orient themselves toward the future through provisional, non-doxastic interpretations of what may happen. These suppositions allow actors to proceed “as if” particular futures were relevant, without requiring commitment to their truth. The article develops a processual model of how futures become socially operative. Possible futures emerge within competing interpretations. They are sustained through uncertainty. They become actionable through selective orientation. As suppositions circulate through communication networks and institutional settings, they acquire salience through repetition, resonance, and amplification. They also enable coordination through second-order suppositions: actors act not only on what they suppose may happen, but on what they suppose others will treat as plausible. By conceptualizing supposition as a mechanism of future-oriented social action, the article advances a sociology of supposition. It shows that the social force of the future lies not in prediction or realization alone. It also lies in the capacity of futures to be collectively supposed, circulated, contested, or rendered impossible.</p>