SFRH/BPD/65009/2009 UID/FIL/00183/2013This essay argues that legal efficacy understood as existent binding force and as dominance of a system of coercion vis-_a-vis competing systems is not strictly a matter of fact, but involves what can be termed justified normativity in a factual context. The argument is divided into four sections. The first three sections describe different dimensions of a normative concept of legal efficacy applied to legal systems: efficacy as persuasiveness, as indirect communication, and as constitutive obedience. The final section focuses on the efficacy of individual norms and adds a new criterion – membership – which establishes a multi-layered test of efficacy.authorsversionpublishe