A fortiori arguments

Abstract

This chapter is devoted to analysing the various uses of the a fortiori argument in legal reasoning. It argues that (i) while the a fortiori argument as usually presented in legal contexts is not logically valid, it is an enthymematic argument (and logically valid once its presupposed premises are all made explicit); (ii) there is reason to think that the nature of such presuppositions is pragmatic, and that expressions such as ‘a fortiori’, ‘all the more’, ‘with stronger reason’, ‘even less’, and so on, function as pragmatic presupposition triggers; and (iii) although the comparison between the source and the target of an a fortiori argument is sometimes drawn through a scalar property that allows for the introduction of relations of transitivity and asymmetry, this is not always the case; there are a range of non-scalar and possibly incommensurable properties that can validate the argument, all related to the normative relevance of the comparison.

I gratefully acknowledge the support of the Spanish government, through the research grants PIF2020-115941GB-100 (AET) and Programa María de Maeztu de Unidades de Excelencia CEX2021-001169-M; and the support of the Generalitat of Catalonia, 2021 SGR 00923 too.