The local court in St. Louis before which this action was brought appears to have made short work of the case.  It had become settled legal doctrine by Lord Mansfield’s decision in the Somersett case, rendered four years before our Declaration of Independence, that “the state of slavery is of such a nature that it is incapable of being introduced on any reasons, moral or political, but only positive law....  It is so odious that nothing can be suffered to support it but positive law.”  The learned chief-justice therefore ordered that Somersett, being claimed as a Virginia slave brought by his master into England, when it was attempted to carry him away against his will, should be discharged from custody or restraint, because there was no positive law in England to support slavery.  The doctrine was subsequently modified by another English chief-justice, Lord Stowell, in 1827, to the effect that absence of positive law to support slavery in England only operates to suspend the master’s authority, which is revived if the slave voluntarily returns into an English colony where slavery does exist by positive law.

The States of the Union naturally inherited and retained the common law of England, and the principles and maxims of English jurisprudence not necessarily abrogated by the change of government, and among others this doctrine of Lord Mansfield.  Unlike England, however, where there was no slavery and no law for or against it, some of the American States had positive laws establishing slavery, others positive laws prohibiting it.  Lord Mansfield’s doctrine, therefore, enlarged and strengthened by American statutes and decisions, had come to be substantially this:  Slavery, being contrary to natural right, exists only by virtue of local law; if the master takes his slave for permanent residence into a jurisdiction where slavery is prohibited, the slave thereby acquires a right to his freedom everywhere.  On the other hand, Lord Stowell’s doctrine was similarly enlarged and strengthened so as to allow the master right of transit and temporary sojourn in free-States and Territories without suspension or forfeiture of his authority over his slave.  Under the complex American system of government, in which the Federal Union and the several States each claim sovereignty and independent action within certain limitations, it became the theory and practice that towards each other the several States occupied the attitude of foreign nations, which relation was governed by international law, and that the principle of comity alone controlled the recognition and enforcement by any State of the law of any other State.  Under this theory, the courts of slave States had generally accorded freedom to slaves, even when acquired by the laws of a free-State, and reciprocally the courts of free-States had enforced the master’s right to his slave where that right depended on the laws of a slave-State.  In this spirit, and conforming to this established usage, the local court of Missouri declared Dred Scott and his family free.