When a judicial doctrine is overruled and a new one is adopted, the new doctrine should be applied prospectively and should not retroactively prejudice parties who had relied on the old doctrine and acted on the faith thereof, especially in the construction and application of criminal laws.

The legal context of this case revolves around the interpretation of firearm laws, specifically the exemption for "peace officers." Initially, in the cases of People vs. Macarandang (1959) and People vs. Lucero (1958), the Supreme Court held that individuals appointed as secret agents with duties related to maintaining peace and order were considered "peace officers" and thus exempt from the requirement of a license to possess firearms. This interpretation was abruptly overturned in 1967 by the ruling in People vs. Mapa, which adopted a strict and literal interpretation of the law, holding that secret agents are not included in the list of exempted persons and are therefore liable for illegal possession. The present case arose from an act committed in 1964, when the old, more lenient doctrine was still in effect, but was decided by the trial court in 1968, after the new, stricter doctrine was established.

• On September 5, 1964, the accused, Jose Jabinal, was found in possession of a .22 caliber revolver and ammunition in Batangas, Batangas.
• The accused admitted to possessing the firearm and ammunition without the necessary license or permit.
• As his defense, Jabinal presented his appointment as a "Secret Agent" by the Provincial Governor of Batangas, dated December 10, 1962, and as a "Confidential Agent" by the PC Provincial Commander, dated March 15, 1964.
• Both appointments expressly authorized him to possess and carry the firearm in question for the purpose of maintaining peace and order and performing his duties.
• At the time of the commission of the offense in 1964, the prevailing jurisprudence (People vs. Macarandang and People vs. Lucero) held that such appointments were a valid defense against a charge of illegal possession of firearms.
• The trial court convicted Jabinal on December 27, 1968, reasoning that the Macarandang and Lucero doctrines had been reversed and abandoned by the Supreme Court in its 1967 decision in People vs. Mapa.

• The petitioner-appellee, the People of the Philippines, represented by the Solicitor General, unconventionally argued in favor of the accused-appellant's acquittal.
• The Solicitor General contended that the conviction should be reversed because the accused-appellant acted in reliance on the prevailing judicial doctrines of Macarandang and Lucero at the time he possessed the firearm.
• It was argued that applying the subsequent Mapa ruling retroactively would be unjust, as the accused-appellant's act was not considered punishable under the law as it was interpreted when the act was committed.

• The defendant-appellant, Jose Jabinal, argued that he was entitled to acquittal based on the Supreme Court's rulings in People vs. Macarandang and People vs. Lucero.
• He contended that at the time he was found in possession of the firearm in 1964, his appointment as a Secret Agent and Confidential Agent constituted a valid and legal justification, as established by the jurisprudence then in force.
• He asserted that the trial court erred in convicting him by retroactively applying the doctrine from the 1967 People vs. Mapa case, which should not affect acts performed when a contrary rule was recognized as law.

• Procedural Issues:
  • N/A
• Substantive Issues:
  • Whether the judicial doctrine established in People vs. Mapa, which abandoned previous rulings favorable to secret agents, should be applied retroactively to convict an accused who committed the act of illegal firearm possession while the previous, more lenient doctrines were still in effect.

• Procedural:
  • N/A
• Substantive:
  • The Supreme Court reversed the judgment of the trial court and acquitted the appellant, Jose Jabinal. The Court ruled that judicial decisions applying or interpreting laws form part of the legal system, and the interpretation of a law by the Court constitutes a part of the law as of the date it was originally passed. Therefore, the doctrines in Macarandang and Lucero were the "law of the land" at the time Jabinal possessed the firearm. When a judicial doctrine is overruled, the new doctrine must be applied prospectively and cannot be used to punish an individual who relied in good faith on the old doctrine. To do otherwise, especially in criminal law, would be unjust as it would punish an act that was not considered punishable at the time of its commission.

• Doctrine of Prospective Overruling — This principle dictates that when a court overrules a prior precedent, the new ruling applies only to future cases and not retroactively to acts that occurred before the new ruling was promulgated. The Court applied this by refusing to retroactively apply the Mapa doctrine to Jabinal, whose actions were justified under the Macarandang and Lucero doctrines that were controlling at the time of his act.
• Legis interpretatio legis vim obtinet — A legal maxim meaning "the interpretation placed upon the written law by a competent court has the force of law." The Court invoked this to emphasize that its prior decisions in Macarandang and Lucero were not merely opinions but were part of the law itself, upon which the public, including Jabinal, had a right to rely until they were overturned.

• "Decisions of this Court, although in themselves not laws, are nevertheless evidence of what the laws mean, and this is the reason why under Article 8 of the New Civil Code, 'judicial decisions applying or interpreting the laws or the Constitution shall form a part of the legal system ***'"
• "...when a doctrine of this Court is overruled and a different view is adopted, the new doctrine should be applied prospectively, and should not apply to parties who had relied on the old doctrine and acted on the faith thereof."
• "Certainly, appellant may not be punished for an act which at the time it was done was held not to be punishable."

• People vs. Mapa — Cited as the 1967 ruling that expressly abandoned the doctrine in Macarandang and Lucero. The trial court used this case as the basis for conviction, but the Supreme Court ruled it should not be applied retroactively.
• People vs. Macarandang — Cited as the controlling jurisprudence at the time of the offense (1964), which held that a secret agent appointed by a governor to assist in maintaining peace and order was considered a "peace officer" and thus exempt from illegal firearm possession laws.
• People vs. Lucero — Cited alongside Macarandang as part of the prevailing doctrine at the time, which similarly acquitted an accused who was granted temporary use of a firearm by a military commander to carry out a lawful purpose.

• Article 8, New Civil Code — Cited to support the principle that judicial decisions interpreting the law form part of the legal system of the Philippines, thereby giving the doctrines in Macarandang and Lucero the force of law at the time they were effective.
• Section 878, Revised Administrative Code — The provision that defines and penalizes the act of possessing a firearm, its parts, or ammunition without a license.
• Section 879, Revised Administrative Code — The provision that enumerates the officials and public servants (e.g., municipal police, provincial governors) who are exempt from the licensing requirements for possessing firearms when used in the performance of their official duties.