Two main theses combine in Bruno Celano’s writings about social ontology and how it relates to law: the first of these concerns the explanatory primacy of the conventionalist over the institutionalist paradigm, as developed by John Searle, while the second concerns the ability of the conventionalist paradigm to throw light on certain theoretically controversial legal phenomena. In the first part of this essay, the author summarises some of the arguments advanced by Celano in favour of the conventionalist model in explaining social facts in general and customary law in particular. In the second part, he focuses on those aspects of law that Celano acknowledges defy explanation in conventionalist terms. Not only do legal conventions have different rates of diffusion and scope in the legal systems - based primarily on customary law - of traditional societies and in those of modern societies, but, above all, the rules whereby legal orders recognise the one and the other type are not liable to any plausible accounting in terms of conventional facts.
Keywords: Bruno Celano - Conventionalism - Customary law - Institutional facts