This article engages with Jane Guyer's assessment (in Marginal Gains, 2004) of contemporary forms of capitalism from outside the bounds of two opposing logics: the universalization of capitalist arrangements versus the specificity of local forms of economic arrangement. Guyer's rejection of a priori definitions of economic categories leads to fertile analysis of measures and mediations as poly-semic modes of valuation. The author asks: what is the theory that would account for or accommodate this polysemy? Corollary questions of epistemology arise regarding distinctions between local conventions and formal procedures and about the criteria that establish such distinctions. Conceding that we attest to the efficacy of economic concepts through practice, the author questions whether these concepts are institutionalized through “experience.” Such concepts (e.g., equivalence) are not merely “economic” in nature; their genealogies disclose the extent to which their efficacy derives from their placement in many domains of life, as artifacts of a general epistemology.