While insisting on a broad understanding of "the liberty of the individual protected by the Fourteenth Amendment," the Lochner Court nevertheless recognized that liberty was subject to regulation for legitimate public purposes.

Under what have been termed the police powers, the states have wide latitude to regulate for the "safety, health, morals, and general welfare of the public."

The Court acknowledged, as it did long before and has long after, that the police powers are somewhat vaguely defined. But even from an expansive understanding of liberty, the key question is whether the law or regulation at issue is plainly adapted to a legitimate public purpose. In Lochner, the Court was skeptical that regulating "the hours of labor in the occupation of a baker," and treating bakers in a manner different from the printer, carpenter, or clerk, was plainly adapted to legitimate concerns of safety, health, morals, or public welfare.

Why bakers? What is the connection between the hours the baker works and "the healthful quality of the bread" he makes? Justice John Marshall Harlan, the great dissenter from Plessy v. Ferguson, also dissented in Lochner, urging that the regulation could be upheld "to protect the physical well-being of those who work in bakery and confectionery establishments."

Just two months before Lochner was handed down, Justice Harlan wrote an opinion in Jacobson v. Massachusetts that upheld a state law allowing local authorities to require vaccinations. Against an outbreak of smallpox, the city of Cambridge required such vaccinations. The Court, recognizing "liberty itself" as "the greatest of all rights," nevertheless insisted that it does not include "an absolute right in each person" to be "wholly freed from restraint." The "safety of the general public" may demand regulations of liberty with regard to public health. All the more so "against an epidemic of disease which threatens the safety of its members." Indeed, an epidemic might justify regulations we would not ordinarily tolerate if the public health and safety required it.