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3.3.3 Sources of Law

By Emilie van den Hoven

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  1. Working definition
  2. Examples of how ‘sources of law’ is used
  3. The meaning of ‘sources of law’ in terms of MoE, affordance, LPbD

Working definition

  1. The sources of law refer to the set of written and unwritten resources from which  binding legal norms are ’drawn’; the sources do not contain information about the law,  they constitute the law as they decide what counts as law 
  2. The sources of law are usually limitatively summed up as: 

    • written sources: 

      1. international treaties  
      2. legislation 
      3. case law
      4. doctrine 
    • unwritten sources: 

      1. fundamental principles, and 
      2. customary law 
  3. Treaties, legislation, case law, fundamental principles and custom present binding legal norms  
  4. A constitution can be written (legislation) or unwritten (customary law); it constitutes the legal powers of the state and the rights of its citizens 
  5. Doctrine contributes to the interpretation of binding legal norms, though it is not binding in itself, the same goes for recitals in treaties, opinions of advocats general (advisors) of highest courts and other formal advisory bodies (e.g. the European Data Protection Board)  
  6. The binding force of fundamental legal principles do not depend on whether or not and how they have been codified in written sources; they are tied up with the core tenets of the rule of law and the moral and institutional grounding of the law. 
  7. Customary law binds due to usus (actual adherence) and opinio necessitatis (a shared sense of obligation) 
  8. To select and apply a relevant legal norm implies an act of interpretation; the act of selection and application cannot be reduced to a logical sequence though it must be justifiable in the form of a syllogism; the need to justify the choice and the interpretation of a legal norm restricts the decisional space of public administration and the courts, thus bringing them under the rule of law 
  9. Interpretation cannot be arbitrary, legal doctrine distinguishes grammatical, systematic, historical and teleological interpretation, i.e. taking into account the ordinary meaning of the relevant terms, the place of the norm within the relevant legal source, the legislature’s intent as derived from official documents, and the aims of the relevant legal source; courts have discretion in selecting and combining these methods of interpretation but the exercise of such discretion is bounded by the demands of legal certainty, justice and purposiveness of the law.

Examples of how ‘sources of law’ is used

A few examples can be given to illustrate what the term ‘sources of law’ means in the legal context:

  • Multilateral international conventions are a source of law for states that ratify them that can become part of the positive law of the domestic legal order in various ways, depending on whether the state in question is has a monist or dualist system.

    • E.g. The Vienna Convention on Road Traffic sets out i.a. the requirements that must be met when driving outside the country of registration. It includes a binding obligation for states to recognize the legality of vehicles from signatory countries.
  • Case law is a binding source of law, and a large number of states also adhere to a rule of binding precedent or ‘stare decisis’.

    • E.g. Someone is apprehended on an outstanding warrant for driving with a suspended license. After the arrest has already been made, the police search the vehicle without a warrant and find drugs. The case is brought to court, which rules that because this search had been conducted without a warrant it violated the Fourth Amendment’s prohibition of unreasonable searches and seizures. This decision is binding as a source of law and sets a rule of precedent that needs to be followed in principle in consequent cases.
    • In coming to the decision whether or not this is a violation of the Fourth Amendment the court must make use in their legal interpretation and reasoning of a fundamental principle of ‘reasonableness’ as source of law in coming to their conclusion.

The meaning of ‘sources of law’ in terms of MoE, affordance, LPbD

As the entry on legal effect has made clear, modern positive law consists of legal speech acts to which we attribute legal effects if a set of specified conditions has been fulfilled. This includes both written and unwritten performatives, i.e. utterances that have legal effect, which are closely connected with institutional facts but also with the so-called sources of law. The term ‘source’ clearly has a very specific meaning in law; sources of law can be seen as the speech acts that are constitutive of the legal norms in a given legal system and set out the preconditions for what else can qualify as a legal norm to which legal effect can be attributed. As Hildebrandt has put it:

A source of law (1) provides legal norms with authority based on their origin, and (2) makes legal norms binding in their effect. First, it refers to the origin or provenance of valid legal norms, that can only be derived from specific sources that thereby give authority to legal norms. […] To ensure legal certainty, only a limited set of sources counts as sources of law: international treaties, legislation, case law, doctrine, fundamental principles and customary law. Only these sources provide legal norms with authority and make them binding in a specific jurisdiction (either national, international, or supranational).1

The sources of law are a key element of the current mode of existence of the law. To explain this further, it is important to recognize the importance of law’s ability to guide our conduct, as channelled through the sources of law, and to do so in a different and more conclusive way than sources of norms like politics or ethics. The sources of law are in large part tied up with the notion of legal certainty, the nature of legal effect as written speech acts and the state’s monopoly of violence. Legal certainty dictates that rules need to be agreed upon beforehand lest we end up having to resort to economic, political, or military power to sort out the disagreements that will inevitably arise. This is why the positivity of modern law is of the utmost importance for legal protection.

As the working definition explains, to select and apply any relevant legal norm implies an act of interpretation which cannot be reduced to a logical sequence (although it must be justifiable in the form of a syllogism); in this way the need to justify the choice and the interpretation of a legal norm restricts the decisional space of public administration and the courts, thus bringing them under the rule of law. However, some sources of law are more straightforward than others: specific legal rules can either be said to apply to a specific situation or case or not, whereas fundamental principles of law are less straightforward in their interpretation and application. Principles of law do not function the same way as rules: they are implied in other legal sources and inform the applicability and application of legal norms and function as part of the ‘implied philosophy’ that guides us in deciding the law. So, deciding what applies to the circumstances and to the facts of a case will require legal reasoning and interpretation in accordance with the implied philosophy of the law — it is a fundamentally thoughtful and deliberative exercise. As the introduction and previous entries in this working paper have borne out, this freedom of interpretation is due to the ‘open texture’ of the law and the multi-interpretability of natural language. It is law’s current mode of existence as a text-driven, and thus inherently adaptive, system that provides the freedom to interpret the law in a variety of ways. This inevitably generates uncertainty, which is seen by some as a bug that needs to be solved but is actually a central feature of the law that affords a distinct type of legal protection ‘by design’, facilitating the possibility to contest that is core to the rule of law.

Legal certainty must be complemented by justice and instrumentality as guiding principles for our interpretive choices in the legal domain.

Legal certainty then, afforded us by the positivity of law and exemplified by the stability offered by the sources of law, is part of the implied philosophy of the law because it allows individuals to plan their lives. So, legal certainty is crucial for providing people with the foreseeability and predictability they require of the law in conducting their everyday lives. However, if we were to focus on legal certainty and concomitant notions of foreseeability and predictability alone as the supreme value of a legal system, we might find ourselves under authoritarian rule or decisionism — in the realm of legalism rather than legality. Therefore, legal certainty must be complemented by justice and instrumentality as guiding principles for our interpretive choices in the legal domain. Balancing the three core values that make up an antinomian understanding of law constitutes an evaluative exercise that requires recognition that these goals of law might be incompatible in particular cases and requires making choices in pursuit of the right balance. 

So, the implied philosophy of law can be understood in Radbruchian terms and taken to include the following notions: (1) legal certainty which, as explained above, entails the need for the law to be stable and foreseeable. This can be taken to denote law’s ‘positivity’ which refers to it being posited by a legislature in accordance with the sources of law and is tied to the state’s monopoly of violence. The sources of law thus carry enormous weight, not as a matter of formalist or legal positivist theory, but as giving validity to legal norms and thereby avoiding the conflation with either politics or morality (which equally does not necessarily imply a strict separation between law and morals); (2) justice, in this context, represents ”the idea of law” which can be understood as the purpose in light of which all of its constituent parts should be constructed. It refers to equality in the sense of ’treating equal cases equally, and unequal cases to the extent of their inequality’.2 This entails striking a balance between distributive and corrective justice, where the former calls for the equal treatment of equal cases and the latter asks that punishment and compensation should be proportional to the harm caused or extent of culpability or wrongfulness.3 Finally, (3) instrumentality entails that the law can be understood as ‘an instrument to achieve a variety of goals that are in part external to its own operations’.4 Instrumentality accounts for the social or political impetus behind a norm but retains its focus on ’what benefits the people’.5  

This all connects us back to speech act theory, as discussed under the entry on legal effect, because this is where law differs from either brute fact and force or propositional logic. We are then once again in the realm of the technologies that afford us the distinct type of legal protection by design that consists in a powerful dynamic between interpretability, contestation and closure that defines text-driven law. Legal certainty, understood in the way that is explained above, originated in context of natural language and the multi-interpretability as afforded by the ICI of written text and the printing press. 


  1. M. Hildebrandt, Law for Computer Scientists and Other Folk (2020, Oxford University Press), pp. 18-19. 

  2. G. Radbruch, ‘Legal Philosophy’ in K. Wilk (ed.), The Legal Philosophies of Lask, Radbruch, and Dabin (HUP 1950), p. 74. 

  3. M. Hildebrandt, Law for Computer Scientists and Other Folk (2020, Oxford University Press), pp. 35-36. 

  4. Ibid. 

  5. G. Radbruch, ‘Statutory Lawlessness and Supra-Statutory Law (1946)’ (2006) 26 Oxford Journal of Legal Studies 1, p. 6. 

This page was last updated on 16 March 2023.