This article employs pragmatist ideas to conceptualise the interdependencies of epistemic instruments and societal futures. Drawing on recent discussions in science and technology studies, it argues that the numerical predictions of computer simulations do not only create novel kinds of future knowledge (epistemic performativity), but also new practices and arrangements of prediction (social performativity). The conceptual framework centres on Dewey's logic of inquiry as the transformation of indeterminate into determinate situations and the role which epistemic instruments such as computer simulations play in this transformation. In order to trace the social performativity of numerical predictions, the paper will provide answers to three questions from a pragmatist perspective. The first question concerns the agency of computer simulations as transformative means in social relations. The second revolves around the impact of these simulations on specific ways of thinking about the future. And, third, the observation and analysis of these changes through empirical research will be addressed.