ABSTRACT
The word ‘source of law’ (‘source de droit’, ‘Rechtsquelle’) has a variety of interpretations.1 The English legal philosopher H.L.A. Hart distinguishes between its use in a ‘material’ or ‘historical sense’ and in a ‘formal’ or ‘legal’ sense.2 In the first non-legal sense it refers to a causal or historical influence explaining the factual existence of a given rule of law at a given place and time, for example, to show that a certain contemporary rule of Dutch law may originate from Roman law, or to state that the development of labour law has resulted from the political action taken by trade unions. In the legal sense, the term means the criteria under which a rule is accepted as valid in the given legal system at issue. These criteria dis tinguish binding law from legally non-binding other social or moral norms and the law de lege lata (the law as it currently stands) from the law de lege ferenda (the law as it may be, or should be, in the future).3 In this sense, the term ‘source’ has a technical meaning related to the law-making process and must not be confused with information sources, research sources or bibliographies on international law.4
