法则 (fǎ zé) is a formal noun meaning 'law', 'rule', or 'principle'—especially one that governs natural phenomena, human conduct, or logical systems. The character 法 (fǎ) means 'law', 'method', or 'standard', while 则 (zé) means 'rule', 'norm', or 'principle'; together, they emphasize an objective, often universal, standard that cannot be arbitrarily changed. Unlike colloquial terms like 规则 (guīzé), 法则 carries philosophical, scientific, or moral weight—common in discussions of physics ('laws of nature'), ethics ('moral laws'), or ecology ('survival of the fittest as a biological law').

It appears frequently in academic, literary, and technical contexts—not daily speech—and rarely stands alone without modification (e.g., 自然法则, 道德法则). Though it can refer to human-made rules, its strongest usage evokes inevitability and universality, similar to English 'law' in 'Newton’s laws' rather than 'traffic laws'.