This paper aims to apply the empirical research on dispute processes to Masaji Chiba's theory on legal pluralism. The task requires a partial modification of Chiba's threedichotomy theory, especially of his first dichotomy between legal rules and legal postulates. The original dichotomy is for comparing the qualitative characteristics of legal formalisation, but modelled on the dual structure of state law. In this paper, I propose an alternative dichotomy for capturing the characteristics of formularising the party's arguments. This paper then explored the dichotomy between formal and substantive ways of legal reasoning. In this paper, I will analyse cases of family disputes observed in Kenyan official and unofficial forums using a revised version of the three-dichotomy theory. The actual cases used in this paper are drawn from the civil disputes concerning the legal conditions of marriage under the customary law of the Gusii community of Kenya.