Piet Fritz Pankratz
University of Vienna
This paper examines the practical role of the sciences in guiding action through a critical reconstruction of what I call the “signpost thesis” in Rudolf Carnap’s scientific humanism (Carnap 1929; 1963). Carnap’s signpost thesis claims that science does not determine ultimate ends but can contribute to decision-making by supplying empirical knowledge and by constraining deliberation through standards of rationality (cf. Damböck 2025). I argue that this thesis rests on an underexamined conflation between two distinct contributions of science: (i) an epistemic one, providing empirically justified information about the world, and (ii) a rationality-related one, supplying standards of rationality for practical reasoning more generally.
I challenge the second claim. While science’s epistemic contribution is relatively uncontroversial, its purported rationality-related role rests on a more demanding assumption: that science alone grounds or exemplifies standards of rationality. Drawing on Ludwig (2025), I argue this cannot be sustained. I show that scientific rationality is no less contingent than rationality outside the sciences. Hence, science does not occupy a uniquely privileged locus of rationality. Instead, standards of rationality are best understood as embedded in a plurality of practices rather than as something anchored in, or exclusively exemplified by, the sciences.
My objection motivates the “signpost-only thesis”. On this view, science contributes to practical reasoning by supplying empirically warranted information, while rationality operates as an independent normative framework for evaluating and integrating such information within practical deliberation. Rational standards apply across domains, including science itself, rather than being grounded in it. This avoids a form of scientism that overextends scientific authority into rationality and yields a more defensible account of science’s role in practical reasoning.
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SOPhiA 2026 