The Latin phrase mutatis mutandis, literally translated as "changing what needs to be changed," constitutes a technique of hermeneutics and legal integration that authorizes the application of a norm, legal institution, or jurisprudential understanding to an analogous situation, through the necessary adaptations to the particularities of the specific case. Operating primarily in the fields of Procedural Law and General Theory of Law, its purpose is to provide cohesion to the legal system, avoiding gaps and ensuring compliance with the principles of equality and procedural economy through the adapted transposition of rules.
1. Concept and Legal Nature of the Institution
In legal parlance, mutatis mutandis is qualified as a technique of interpretative adaptation. It is not to be confused with pure analogy (analogia legis), although it shares an ontological kinship with it. While analogy seeks to fill an absolute normative gap, the application mutatis mutandis presupposes the existence of a norm or precedent that, although intended for a different hypothesis, possesses a ratio decidendi or factual-legal basis that is compatible, requiring only peripheral adjustments for its incidence.
Its legal nature is that of a tool for integration and subsidiary or supplementary application. It is a postulate of formal logic applied to Law, based on the premise that legally similar situations should receive analogous treatment, respecting inevitable procedural or material distinctions.
2. Historical Origin and Evolution in Law
Although the expression has roots in medieval scholastic Latin, its application was consolidated in the Common Law tradition and, subsequently, in Civil Law systems. Historically, the term was used in international treaties to allow clauses of an agreement to be extended to new signatories without the need for a total rewriting of the text.
In Brazilian Law, the evolution of the institution follows the transition from strict legalism to a model of binding precedents. The need for uniformity in jurisprudence, accentuated by the procedural reforms of 2005 and the enactment of the 2015 Code of Civil Procedure (CPC/15), transformed mutatis mutandis into an essential mechanism for applying theses established in Repetitive Appeals and General Repercussion to factual contexts that, although not identical, share the same legal essence.
3. Legal Provision and Normative Foundation
The application of the mutatis mutandis principle finds direct and indirect support in various statutes of the national legal system:
- Law of Introduction to the Norms of Brazilian Law (LINDB), Art. 4: Establishes that "when the law is silent, the judge shall decide the case in accordance with analogy, customs, and general principles of law." Mutatis mutandis operates as the operational vehicle for this analogy.
- Code of Civil Procedure (CPC/2015), Art. 15: Determines that, in the absence of regulating norms, the provisions of the CPC shall be applied "supplementarily and subsidiarily" to electoral, labor, or administrative proceedings. This subsidiary application is, by definition, an application mutatis mutandis.
- Code of Criminal Procedure (CPP), Art. 3: Admits extensive interpretation and analogical application, as well as the supplement of general principles of law, grounding the transposition of civil procedural guarantees to the criminal rite, observing the necessary adaptations to freedom of movement.
- Consolidation of Labor Laws (CLT), Art. 769: Provision for the application of common procedural law in labor proceedings, in cases of omission and compatibility.
4. Practical Application and Consolidated Jurisprudence
The jurisprudence of the Superior Courts uses the technique to provide effectiveness to constitutional and procedural norms. The following applications stand out:
4.1. Supreme Federal Court (STF)
The STF frequently applies mutatis mutandis in constitutional review and in writs of injunction (mandados de injunção). A classic example lies in the application of the Strike Law (Law No. 7.783/89) to civil public servants. Given the legislative omission, the STF determined, in the judgment of MIs 670, 708, and 712, that the rules of the private sector apply to the public sector mutatis mutandis, adapting the exercise of the right to the unavoidable needs of the Public Administration.
4.2. Superior Court of Justice (STJ)
In the STJ, the technique is fundamental in the application of the Consumer Defense Code (CDC). The Court consolidated the understanding that the protective norms of the CDC apply to contracts governed by specific laws (such as the Housing Financial System or banking contracts), provided that the adaptations preserve the specialty of the sectoral norm. A recent example is found in the application of theses on the Theory of Substantial Performance, transposed from generic civil contracts to fiduciary alienations, with the pertinent reservations regarding the nature of the guarantee.
4.3. Superior Labor Court (TST)
With the advent of the CPC/2015, the TST issued Normative Instruction No. 39/2016, which expressly provides for which norms of the new Code of Civil Procedure apply to Labor Proceedings. The application provided therein is essentially mutatis mutandis, since it requires compatibility with the principles of celerity and protection of the weaker party.
5. Correlated Principles and Doctrinal Divergences
The institution dialogues directly with the Principle of Legal Certainty and the Principle of the Unity of the Legal System. Contemporary doctrine, led by jurists such as Lenio Streck and Fredie Didier Jr., discusses the limits of this transposition. The main divergence lies in the risk of "activism by analogy," where the magistrate, under the pretext of applying a norm mutatis mutandis, ends up creating a new legal rule (legisferar), violating the separation of powers.
For the majority current, the application must respect the Criterion of Ethical-Legal Compatibility: the transposed norm cannot annihilate the substance of the destination institution. If the necessary adaptation is so profound that it distorts the original norm, mutatis mutandis becomes inapplicable, and the interpreter must seek another form of integration.
6. Contemporary Relevance and Practical Impacts
Currently, the expression plays a vital role in Digital Law and the regulation of new technologies. Given the absence of specific legislation for artificial intelligence or digital assets, the Judiciary has applied traditional civil liability regimes and norms of the General Data Protection Law (LGPD) mutatis mutandis to resolve emerging conflicts.
The practical impact is the reduction of legal uncertainty. By allowing the stock of already consolidated legal and jurisprudential knowledge to be leveraged in new fronts, the system gains predictability. However, it requires the legal practitioner to exercise redoubled technical rigor to justify which "changes" are being made, under penalty of nullity of the decision due to lack of adequate reasoning (Art. 489, § 1, of the CPC).
Legal and Jurisprudential References
- BRAZIL. Constitution of the Federative Republic of Brazil of 1988.
- BRAZIL. Law No. 13.105, of March 16, 2015. Code of Civil Procedure.
- BRAZIL. Decree-Law No. 4.657, of September 4, 1942. Law of Introduction to the Norms of Brazilian Law (LINDB).
- STF. Writ of Injunction No. 708/DF. Rapporteur: Justice Gilmar Mendes. Judged on 10/25/2007.
- STJ. Precedent (Súmula) No. 297: "The Consumer Defense Code is applicable to financial institutions."
- TST. Normative Instruction No. 39/2016. Provides for the norms of the 2015 CPC applicable and inapplicable to Labor Proceedings.
