Throughout his scientific work, the Argentine lawyer E. Bulygin repeatedly analyzed the problem of the validity and efficacy of law. Based on the formulations of H. Kelsen’s pure theory of law, E. Bulygin sought to explicate the concepts of legal validity and efficacy, i.e. to replace them with new more accurate ones.
In the 1965 paper "The Concept of Validity" Bulygin entered into a polemic with H. Kelsen and A. Ross and formulated the concept of efficacy as a dispositional property of the legal norm reflecting its justiciability. Subsequently, however, the Argentine lawyer clarified his terminology and distinguished between the dispositional concept of efficacy (law in force) and the traditional notion of efficacy because of the conclusion on the expediency of using the old concept of efficacy along with the new one defined through justiciability. But the concept of efficacy as justiciability formulated by E. Bulygin faced a number of theoretical difficulties. In the 1966 paper "Judicial Decisions and the Creation of Law" E. Bulygin made an attempt to explicate the concept of validity. E. Bulygin points to three concepts designed to replace the traditional notion of validity: the validity of the norm in the system sense, the binding force of the norm and the existence of the norm. Each of these specified concepts was developed in theoretical constructions of the Argentine lawyer, however their using also generates the problems. Alternatively, the development of the notion of validity of law in the system sense can be considered "definitive" concept of validity proposed by E. Bulygin in collaboration with K.E. Alchourron in the monograph "Normative systems" (1971). However, this concept has significant differences from the originally formulated and has a very limited application. The concept of the existence of the norm does not receive independent development as a variant of the explication of the concept of the validity of law. The concept of the binding force of law, on the contrary, is divided by the Argentine jurist into two fundamentally different concepts — binding force in the metaphysical sense and binding force in the technical sense, which later E. Bulygin called "applicability". The concept of applicability was used by the Argentine legal philosopher to solve a number of problems of H. Kelsen’s theory, however the concept of applicability itself leads to paradoxical consequences. On the whole E. Bulygin’s project of explicating of the concepts of validity and efficacy of the law didn’t result in replacing them with series of new more precise concepts although refined in some way their meaning.