[3] Even more fundamentally, use of police power draws on two Latin principles, sic utere tuo ut alienum non laedas ("use that which is yours so as not to injure others"), and salus populi suprema lex esto ("the welfare of the people shall be the supreme law"), to justify restriction of individual liberties in order to protect the general welfare.
In Commonwealth v. Alger, Chief Justice Lemuel Shaw wrote that "It is much easier to perceive and realize the existence and sources of [the police power] than to mark its boundaries, or prescribe limits to exercise.
Laws must apply equally to all under like circumstances... government interferences with individual rights must be 'reasonable' – they must have a clear relation to some legitimate legislative purpose.
"[4] Later court cases have expanded somewhat on these restrictions by limiting the ability of states to infringe upon implied constitutional rights and by demanding a stricter standard of reasonability, but regulation of police power remains fairly minimal.
The decision by the Massachusetts Supreme Judicial Court in the case Commonwealth v. Alger (1851) was related to land-use planning and dealt with the construction of a wharf on privately-owned tidelands around Boston Harbor.