This article explores a mapping of the formal probability calculus onto the informal logic concepts of acceptability and sufficiency, concluding that while this approach is technically feasible, its value for understanding real-life arguments is limited. This article was originally published as: Black, J. (1991). Quantifying support. Informal Logic, 13(1), 21-30. DOI: 10.22329/il.v13i1.2548 Informal Logic is an open access, peer reviewed journal from the University of Windsor Centre for Research in Reasoning, Argumentation and Rhetoric, which publishes articles and reviews on topics related to reasoning and argumentation in theory and practice. For more information about the journal visit: https://ojs.uwindsor.ca/index.php/informal_logic/. This article can also be viewed at: http://dx.doi.org/10.22329/il.v13i1.2548. https://viurrspace.ca/bitstream/handle/10613/6607/Black.J.IL.1991.pdf?sequence=3