Prospectivity of jurisprudence

Decisions of the Supreme 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." (G.R. No. 100776, October 28, 1993)

The interpretation upon a law by the High Court constitutes, in a way, a part of the law as of the date that law was originally passed, since this Court's construction merely establishes the contemporaneous legislative intent that the law thus construed intends to effectuate. The settled rule supported by numerous authorities is a restatement of the legal maxim "legis interpretation legis vim obtinet" — the interpretation placed upon the written law by a competent court has the force of law. (G.R. No. 100776, October 28, 1993)

When a doctrine 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. This is especially true in the construction and application of criminal laws, where it is necessary that the punishment of an act be reasonably foreseen for the guidance of society. (G.R. No. 100776, October 28, 1993)