Ignorance of the law

Ignorance of the law excuses no one from compliance therewith. (Article 3 of the Civil Code of the Philippines) This means that there is a conclusive presumption that everyone knows the law, even if they have no actual knowledge of the law as long as there has been publication.

The laws referred to by this article are those of the Philippines. There is no conclusive presumption of knowledge of foreign laws. Foreign laws must be proved as a matter of fact in our courts.

Publication is notice to all of the contents of the law. If there is valid publication, the law becomes effective and no one can interpose the defense of ignorance. If there is no valid publication, ignorance is a defense.

Tolentino posits that mistake of fact and mistake regarding doubtful or difficult questions of law  may excuse a party from the legal consequences of his conduct; but not ignorance of law. In specific instances provided by law, mistake as to difficult legal questions has been given the same effect as a mistake of fact.
A mistake of law cannot be used as a lawful justification because everyone is presumed to know the law and its consequences. Ignorantia legis neminem excusat. (G.R. No. 231730)

Ignorance encompasses not only substantive but also procedural laws. (G.R. No. 151047)

While an honest mistake of fact could be used to excuse a person from the legal consequences of his acts as it negates malice or evil motive, a mistake of law cannot be utilized as a lawful justification, because everyone is presumed to know the law and its consequences. Ignorantia facti excusat; ignorantia legis neminem excusat.. (B.M. No. 2540)

J. VELASCO'S DISSENT IN CIR v. SAN ROQUE: Thus, if, as the Decision declares, “[t]axpayers should not be prejudiced by an erroneous interpretation by the Commissioner, particularly on a difficult question of law,” there is more reason to maintain that refund seekers should not be prejudiced, penalized nor castigated for having taken guidance from the policies, pronouncements, issuances and actuations of the BIR and the CTA, which actuations have direct bearing on a difficult question of law.

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This Court is, therefore, duty-bound to actively refrain from actions that may be perceived as elevating strict adherence to procedural rules and technicalities over and above the taxpayer’s clear, substantive legal right to the refund sought. We must remain cognizant of the taxpayer’s good faith compliance with procedures approved and sanctioned by the BIR and the CTA and accepted by this Court, and avoid creating obstacles to defeat the taxpayer’s substantive right to refunds. (G.R. No. 187485)