Pennsylvania Coal Co. v. Mahon

Justice Holmes began from the premise that government may regulate property and diminish some of its value without compensating every affected owner. Property rights are held subject to implied limits imposed by the police power. But those limits are not boundless: if regulation reaches a sufficient magnitude, it must be treated as an exercise of eminent domain and supported by just compensation. The constitutional question therefore turns on the particular facts and the degree of the burden imposed.

The burden here was exceptionally severe. Under Pennsylvania law, the reserved right to mine the coal was a valuable estate in land, and the deed gave the company a binding contractual right to remove the coal even if the surface subsided. Because the practical value of coal lies in the ability to mine it profitably, a rule making mining commercially impracticable has nearly the same constitutional effect as appropriating or destroying the coal itself.

The asserted public interest did not justify this extensive destruction of the company’s rights. The immediate controversy concerned a single private house, and damage to that house was not a public nuisance merely because similar subsidence might occur elsewhere. The statute itself also showed that its protection was limited, because it generally did not apply where the same person owned both surface and coal rights.

Nor could the Act be defended chiefly as a safety measure. The company had given notice of its intention to mine, and the Court concluded that notice could protect occupants from personal danger. In the Court’s view, the statute primarily shifted to the coal owner the financial loss resulting from the surface owner’s decision to acquire surface rights without purchasing a right of support.

The Court stressed that a strong public desire to prevent subsidence does not permit the government to obtain the desired protection through regulation when the Constitution requires payment. Pennsylvania could address a genuine exigency through eminent domain, but it could not force the owner of the reserved coal estate alone to bear the cost of the public or private protection sought. Holmes expressed the governing principle in enduring terms: property may be regulated to a certain extent, but when regulation goes too far, it is a taking.

The Court addressed the Act’s broader application because Pennsylvania’s Attorney General, the City of Scranton, and other interested groups had participated and sought resolution of the statute’s general validity. It held that public ownership of a street did not supply a basis for taking additional support rights without payment when the public had acquired only surface rights.

A public entity’s rights in a street acquired by purchase or condemnation are limited to the rights it paid for. If it obtained the surface but not a right of subjacent support, the Court reasoned, the public’s need for that support did not authorize the State to supply it at the coal owner’s expense. The appropriate constitutional route was to acquire the support right through eminent domain and pay compensation.

The Court distinguished a prior decision allowing Pennsylvania to require coal pillars along adjoining mine boundaries. That requirement protected miners from flooding dangers and provided an average reciprocity of advantage among neighboring mine owners. By contrast, the Kohler Act imposed a concentrated and near-total loss on owners of reserved coal rights for the benefit of surface owners and the public, without comparable reciprocal benefit or compensation.