Across legal systems, certain Latin maxims have endured for centuries because they embody fundamental notions of justice, legal certainty, fairness, and accumulated judicial experience.
These principles provide courts and parties with guidance when interpreting rights and obligations, particularly where parties seek to extend or restrict legal duties beyond the scope contemplated by legislation or contractual agreements.
Thus, principles such as pacta sunt servanda, res inter alios acta, ex aequo et bono, res judicata, and inveterata consuetudo continue to influence judicial reasoning and practical legal outcomes.
Their authority, however, differs significantly between civil law and common law jurisdictions. This article examines those differences through a practical case arising before Mexican courts.
As an example, doctrine is not regarded as a formal or main source of law within the Mexican legal system and is afforded considerably less authority than it enjoys in common law jurisdictions. This distinction represents one of the fundamental differences between the two legal traditions. Consequently, building a defence primarily around a legal doctrine or principle can be challenging in a civil law jurisdiction, particularly when applicable federal legislation may point towards a different legal outcome or interpretation.
Of course, some legal principles are already reflected in federal legislation, such as pacta sunt servanda. Others, however, are either absent from statutory law or may appear irrelevant when a dispute depends primarily on the interpretation of federal codes, which remain the principal source of law within the Mexican legal system. The following case illustrates this point
A practical case involving
Public Procurement and a Subcontractor's Commercial Claim An instructive first-hand example arose in a dispute in Mexico involving a subcontractor and a contractor engaged in a power-generation project exceeding 1,000 MW. The project had originally been commissioned through a public procurement procedure.
A Mexican public entity awarded the principal contract to a global contractor under the Federal Public Works Law following a competitive public tender process governed by federal public law.
The contractor, wholly owned by a European company, subsequently entered into a separate subcontract with a Mexican company for the performance of part of the works. The subcontract expressly stated in its recitals that the project had been awarded by a public entity pursuant to the Federal Public Works Law and that the resulting assets would ultimately be owned and operated by the Mexican State. The subcontract also incorporated several back-to-back provisions.
A dispute later emerged between the contractor and the subcontractor. The subcontractor argued that, because the project originated from a public procurement procedure governed by public works legislation and because the infrastructure would ultimately belong to and be operated by the Mexican State, the relationship between the contractor and subcontractor could not be regarded as a purely commercial arrangement. Consequently, the subcontractor contended that the Federal Public Works Law should also govern the dispute.
Furthermore, the subcontractor argued that it was a matter of ordre public that the relationship be regulated under the Federal Public Works Law because the project served a public purpose, would ultimately be financed through public resources, and would contribute to the Mexican electricity system.
At first glance, this appeared to be a compelling argument before a Mexican court, particularly given its public-interest and national-policy dimensions.
The subcontractor further relied on the principle of lex specialis derogat legi generali ("special law prevails over general law"). Under this principle, when two laws of equal hierarchical rank appear to conflict, the more specific law generally takes precedence over the more general one.
Subcontractor's intention was clear since the court should determine that the highly specialised legal framework established by the Federal Public Works Law prevailed over the Commercial Code, even though both enjoy the same hierarchical status within the Mexican legal system. This distinction was strategically important because the Federal Public Works Law imposed significantly stricter obligations upon the contractor than the Commercial Code.
In response, contractor relied upon another principle: res inter alios acta. The argument was developed from a doctrinal and academic perspective because the principle is not expressly codified under Mexican law.
The principle provides that agreements, acts, or legal relationships between certain persons cannot generally impose obligations or confer rights upon third parties who are strangers to those arrangements. In modern contract law, it closely resembles the doctrine of privity of contract. A person who is not a party to a contract ordinarily cannot enforce it nor be burdened by its obligations. The principle promotes legal certainty by ensuring that parties are bound only by legal relationships they have voluntarily accepted.
Subcontractor's position nevertheless appeared strong because neither applicable statute expressly addressed the specific circumstances of the dispute. Moreover, the points of connection linking the subcontract to the Federal Public Works Law had been carefully and convincingly articulated.
The role of Doctrine in civil law
The legal reasoning underpinning this dispute would be readily familiar to any common law practitioner. However, the role of doctrine differs considerably between common law and civil law systems because the structure and sources of law in each tradition are fundamentally different.
In common law systems, legal doctrine is largely developed through judicial decisions. Courts create and refine legal principles through case law, and those principles become part of the law through the doctrine of stare decisis, under which precedents are generally binding upon lower courts.
In civil law systems, by contrast, judicial decisions derive primarily from constitutional principles, legislative codes, and statutory provisions. Courts principally apply and interpret legislation rather than create law through precedent. Although judicial precedent and jurisprudence may have persuasive authority, and in some circumstances binding authority, courts generally begin their analysis with the applicable code or statute.
As a result, courts are typically under no obligation to decide a case solely on the basis of doctrine. Doctrine therefore occupies a subsidiary position within the hierarchy of legal sources. We were fully aware of this reality when formulating our defence strategy.
The court's decision
Faced with competing legal principles and two federal statutes occupying the same hierarchical level within the Mexican legal system, the court ultimately accepted the defence based on res inter alios acta.
The court reasoned that, although the project originated from a public tender conducted by a governmental entity for the construction of publicly owned infrastructure, the public procurement contract was a legal arrangement existing solely between the public authority and the principal contractor.
The rights and obligations arising from that contract could not automatically be extended to a subcontractor that was not a party to the original agreement, notwithstanding the various express and implied connections between the subcontract and the Federal Public Works Law.
In other words, the procurement contract was truly res inter alios acta; it was a matter between others.
The subcontractor sought to rely upon legislation and contractual obligations arising from a separate legal relationship, even in the presence of back-to-back provisions. However, the court concluded that the subcontract remained an autonomous contractual arrangement governed by its own terms. Consequently, the public procurement rules applicable to the principal contract were not automatically incorporated into the subcontract, even though the recitals described the public nature of the project, the legal framework under which it had been awarded, and the identity of the public authority involved.
The practical consequences were significant. As noted above, the public procurement provisions invoked by the subcontractor imposed stricter obligations and potentially more burdensome liabilities upon the contractor.
Yet the case demonstrates an important lesson. Even within a civil law system, where legislation remains paramount and doctrine has only secondary authority, legal principles continue to influence judicial reasoning. Under the right circumstances, a doctrine that formally occupies a marginal place within the legal hierarchy may nevertheless prove decisive in determining the outcome of a dispute.
