Natural law and casuistic reasoning in Roman jurisprudence

“The Roman jurists, 'calculating with concepts', did not need any natural law” (Christoph Kletzer). Focusing on the Classical juristic material in Justinian’s Digest, in addition to Gaius’ Institutes, this essay argues that natural law was in fact one concept, amongst others, that Roman jurists calculated with. There is no evidence for any Roman juristic treatises dedicated to natural law, yet as Levy noted in 1949: “Hundreds of texts are concerned with ius naturale, naturalis ratio, rerum natura and other phrases related to natura or naturalis. It is impossible to find a common denominator”. The essay divides into two parts: first, it surveys a series of arguments drawn from those 'hundreds' of Roman juristic texts that relate to natural reason and natural law(s). Second, it analyses the Roman juristic method of ‘calculating with concepts’. The argument throughout is that the ‘common denominator’ that eluded Levy is the Roman jurists own, highly particular, type of case-methodology.