In recent years, a growing number of legal scholars have revived the interest in the legal philosophy of Alf Ross (1899–1979) (see, e.g., Holtermann and Madsen 2015; Krešić 2019). This trend is well illustrated by the new English translation of Om ret og retfærdighed (Ross 1953) published by Oxford University Press (Ross 2019), and by the first translation into Italian of the almost forgotten Kritik der sogenannten Praktischen Erkenntnis (Ross 1933; 2020). The revival is justified by the prominent role and great influence that Alf Ross has on the European debate—an influence that extends far beyond the boundaries of legal philosophy—and by the fact that several elements of his complex theory need clarification. Moreover, the radical research program Ross proposed between 1929 and 1968 is still highly relevant at a time when both the social sciences and philosophy are dominated by empirical and behavioral approaches. Ross proposed a research agenda for the analysis of the legal materials based on the radical empiricism that characterizes any form of legal realism: As Brian Bix explains in the article published in this issue, Ross understands legal rules as patterns of behavior supported by a shared (legal) ideology qua aggregate of doctrinal assumptions, fictions, and dogmatic constructions (Ross 2019, 48). Accordingly, a (genuine) general jurisprudence can map out the governing rules through verifiable “empirico-scientific assertions about social reality” (ibid., 51). The question raised by Bix is: Does Ross take issues of prediction seriously? Ross rejected legal methods oriented toward the deductive identification of (formally) valid law. In this context, he postulated a fundamental distinction between “formally valid law” (gyldig ret)—the law as it is correctly promulgated—and “scientifically valid law” (gældende ret)—the system of legal rules, which are expected to be applied by the courts, mapped through probabilistic inferences (Ross 2019, 44–57, 78–85). This distinction, which was lost in the first English translation of Om ret og retfærdighed (Ross 1953; trans. Ross 1958; see also Ross 1998, 158), and prompted H. L. A. Hart's misguided criticisms (Hart 1955; 1959), is at the heart of Alf Ross's theory establishing the “dual nature” of law (Ross 1946, 20). Scientifically valid rules are motivated by a general consciousness of the law (Ross 2019, 85–6) and are endowed with efficacy (Wirksamkeit). I leave aside here the well-known “translation conundrum” (Eng 2011; Holtermann 2019) and assume pro tanto that “scientifically valid” is a possible English equivalent of gældende ret. Taking cues from the concept of gældende ret, Ross denounced the temptation to reduce the concept of law to a system of imperatives enacted by legislators: “[A] realistic doctrine of the sources builds on experience, but recognizes that not all law is positive, in the sense of ‘formally established’” (Ross 2019, 100; see also Ross 1929, 219–29). According to Ross, law is primarily a social institution distinct from morality (Ross 1946, 121); legislative intent is a hypostatization similar to the Volkgeist of the Historical School (Ross 1929, 184–91). Since law is a social phenomenon, rooted in the Handlungstotalität, it also seems implausible to postulate a “pure” concept of law: Even Hans Kelsen's Neo-Kantian apparatus (Paulson 1992) represented for Ross only a form of “quasi positivism” (Ross 1929, 270–88; 1968, 156; 2019, 41–50). Instead, following the Scandinavian realist Axel Hägerström, Ross traced law back to its factual dimension: A realist conception of legal phenomena “in principle and consistently considers the law as a set of social facts—a certain human behavior and ideas and attitudes connected with it—and the study of the law as a ramification of social psychology” (Ross 1946, 9). This characterization, which embodies a naturalized legal positivism, stands in contrast to forms of positivism without naturalism (Paulson 2011), which in turn view legal validity as an a priori. Svein Eng's contribution on Ross published in this issue partly challenges the traditional perception of the Ross-Kelsen debate by offering new arguments to show how the “[t]he disagreement between Kelsen and Ross is not one of philosophical principle […] but one that must be resolved on the basis of pragmatic considerations”—a disagreement that can ideally be resolved through Carnap's distinction between “internal” and “external” questions, “conceptual features” and “contextual presuppositions” (Carnap 1956, 206–14). The metatheoretical investigations of the competing positions that Ross develops—thoroughly analyzed by Giorgio Ridolfi—are characterized by a strong antimetaphysical attitude toward practical reasoning. Based on what seems to me a method of immanent critique, Ross presents each and every normative theory of practical rationality as self-contradictory. Ridolfi compares Ross's metaethical inquiry with Marxist materialism and practical nihilism. For Ross, law is ultimately an observable phenomenon rooted in the emotional experiences of individuals, and externalized through a particular behavior. The notion of formal validity, therefore, does not denote a category—or a form of cognition—but rather a bundle of subjective experiences and impulses triggered by mental representations of legal sources and concepts. The addressees of “directives” issued by a (presupposed) authority must recognize them as binding in order to transform these peculiar semantic contents into norms (Ross 1968). Bindingness and efficacy are linked to the feeling of constraint: the feeling of being bound to the prescribed pattern of behavior (Ross 1946, 176). Of course, not every experience of coercion is also an experience of obligation. I certainly feel compelled, but not under obligation to, hand over my valuables to a robber who attacks me with threats and violence. (Ross 1933, 276) The primary rules are duty-imposing; they are immediately concerned with the behavior required by human beings. The secondary rules are power-conferring; they provide that human beings under certain conditions shall have the power (competence) to create by their acts (acts in law) new rules belonging to the system. (Ross 1962, 1185) In view of what has just been said, the objection of “quasi-positivism” that Ross levels at Kelsen throughout his intellectual production is an obvious implication of these premises (Ross 1929, 3–7, 219–29). For Ross, ought and validity are not categories: They are rationalizations motivated by the experience of a duty that creates an illusion of objectivity. Thus, Kelsen's assertions of “validity” are expressions of pseudopropositions: manifestations of a metaphysical idea of authority. Ross acknowledges that law presupposes the notion of empowerment (or “competence”); however, empowerment needs to be disentangled from a purely formal notion of authority. In Ross's view, the sources of law cannot be determined statically, as their list evolves dynamically: Starting from the idea of competence, jurists regard as valid law both a set of formal sources (e.g., authoritative decisions) and a variety of substantive sources, which include practical considerations, ideologies, and, more generally, any motivating factor recognized as a valid element by the particular legal culture (Ross 1929; 1946, 141). This statement comes with a caveat: Not every motivating factor that determines a judge's decision is part of the law, but only those motivating factors that (through habitual repetition) the judiciary regularly associates with notions of validity and competence. In contributing to this issue of Ratio Juris, Brian Bix, Svein Eng, and Giorgio Ridolfi bring new insights to a longstanding and now revived debate, and so a fresh perspective on the theory of one of the 20th century's leading exponents of legal philosophy.