The most common distinction noted is probably the difference in the way in which the two Western traditions approach codes and case-law. The standard axiom is that civil law systems are based on codes, and common law systems are based on case-law. Civil law systems commonly trace their ancestry to the 6th Century and the Roman Emperor Justinian’s massive codification project, the Corpus Juris Civilis. Common law systems typically trace their ancestry to England and judicial decisions dating back to the early period of the British royal monarchy. However, today, this distinction in and of itself does not prove particularly enlightening. Common law systems have massive codes comparable to civil systems, and civil law systems increasingly embrace case-law in some form. Where the differences are more significant is at the conceptual level.

In civil law systems, the core codes share a similar architecture by design. As a general proposition, all civil law systems base their legal system on four codes: the civil code, civil procedure code, criminal code, and criminal procedure code. These codes are drafted as a coherent set of principles that are intended to provide an organic framework from which the rest of the legal system can be structured. Given the organic nature of these laws, a civil law lawyer frequently commences his or her legal research consulting one of these codes.

In contrast, common law codes do not generally share such a coherent structure, and they are frequently more detailed and case specific. This approach reflects a more piecemeal approach to the drafting of laws, which is typically driven by contemporary events and circumstances arising in case-law. Thus, though a common law legal practitioner may also start his or her research with a code provision, there is a high degree of likelihood that case-law will need to be consulted immediately to fully appreciate the underlying principles and considerations.

Moreover, the common law doctrine of stare decisis requires this attention to case-law, for the failure to identify and analyze the relevant cases could be tantamount to malpractice. Case-law precedent is law in the common law system, and a judge is required to apply precedent to cases before him or her. Thus, a single, controlling decision from a higher court may be dispositive of a particular controversy. Outside of the constitutional realm, a single case would generally not be considered to have such dispositive force in a civil law system. For case decisions to have a similar effect, they must reflect an established pattern of decision-making. A series of cases enunciating and supporting the same rule is required, and only when this consistency is present will legal scholars classify the case-law as jurisprudence constante, signifying an established, persuasive line of legal reasoning.