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Abolitionists declared their first major victory in 1772 with the Somerset case, which was popularly interpreted as outlawing slavery in England. In ruling on the case, Lord Mansfield consulted with the great legal theorist William Blackstone, whose four‐volume Commentaries on the Laws of England (1765) was required reading for students of law in England and America and “ranked second only to the Bible as a literary and intellectual influence on the history of American institutions.” Blackstone's understanding of slavery was richly ambiguous. On the one hand, he argued that only a positive law sanctioning slavery could override the natural law of freedom. On the other hand, he suggested that in certain circumstances natural law could trump positive law. Although Lord Mansfield based his decision in the Somerset case primarily on the precedent of villeinage, arguing that slaves could not be treated worse than villeins and thus could not forcibly be removed from England, Blackstone nevertheless contributed to its antislavery interpretation. British lawyers defending the slave James Somerset relied on Blackstone to argue that slavery was contrary to natural law; and Lord Mansfield acknowledged this while ruling in their favor. Somewhat inadvertently, Lord Mansfield established a precedent for Blackstone's theory that slavery could be sanctioned only by positive law. According to the legal scholar Robert Cover, the Somerset decision “gave institutional recognition to antislavery morality.” It influenced the gradual abolition of America's northern states, including Vermont's Constitution of 1777 (the first constitution in history to outlaw slavery), and the Quock Walker case of 1783, which effectively ended slavery in Massachusetts. Blackstone's Commentaries, coupled with the Somerset decision, would contribute to the antislavery platforms and ideologies of the Liberty, Free‐Soil, and Republican parties.
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