A political normative rule holding that the state or others may legitimately restrict an individual's liberty only to prevent actions that cause or create a significant risk of harm to other persons; conduct that affects only the actor’s own interests ordinarily falls outside the scope of permissible interference.

Principle

Limit coercion to cases where an action either causes harm to others or creates a non‑trivial, reasonably foreseeable risk of such harm; mere offense, self‑regarding immorality, or riskless private choice do not by themselves justify restriction.

Demonstration

Illustrative scenario — Situation: A municipality considers regulating loud late‑night parties. Recognition: Authorities assess whether noise creates health‑related harms or significant disruption to neighbours. Action: They adopt targeted noise limits and enforcement limited to demonstrable harms (e.g., sleep disruption causing health effects). Consequence: Individual leisure activity is constrained only where it demonstrably infringes others’ well‑being; purely private conduct without external harm remains lawful.

Misapplication

Mistaken interpretation: treating any morally offensive or unpopular conduct as 'harm' warranting prohibition. Why it appears plausible: moral disapproval often correlates with calls for regulation. Semantic error: conflating offence, disgust or moral condemnation with the causal notion of harm (injury, risk, or rights violation). Correct interpretation: justify interference only by demonstrable harm or significant risk to others.

Consequence

Establishes a high threshold for legal or coercive intervention, protecting personal autonomy and pluralism; it also requires definitional and evidentiary work to specify what counts as harm and to distinguish harms from mere offence or private risk.

Reversal

Qualification: in contexts of grave collective threats (e.g., epidemics, imminent large‑scale harms), fiduciary or public‑health duties and background institutional rules can permit broader restrictions; similarly, when actions create systemic externalities the threshold for intervention lowers.

Boundary

Clearly within: laws prohibiting assault, fraud, or unpermitted environmental contamination that directly injure others. Boundary case: speech that offends a group but does not produce demonstrable harm — applicability depends on empirical proof of harm and proximate causation. Clearly outside: purely self‑regarding acts that produce no foreseeable harm to others (e.g., private consensual acts between competent adults) absent other legal grounds.

Semantic Tension

Individual Liberty ↔ Public Protection: preventing interpersonal harm requires limiting some liberties, producing a recurring need to specify harm, risk thresholds and evidentiary standards.

Synthesis

The Harm Principle centers legitimacy of coercion on interpersonal harm and causation; applying it requires careful empirical and normative specification of what counts as harm and how risks translate into permissible restrictions.