Woolman's powerful essays, Some Considerations of the Keeping of Negroes (1754) and Considerations on Keeping Negroes (1762), and Benezet's Epistle of Caution and Advice Concerning the Buying and Keeping of Slaves (1754) and Some Historical Account of Guinea (1772), occasionally pass over the line separating religious antislavery and the secular antislavery that has generally been viewed as embracing a broader narrative receptive to international influences. Woolman, for example, argued vaguely that Africans also enjoyed the "natural right of freedom," while Benezet quoted directly from the French philosopher Montesquieu's Spirit of the Laws (1748). Through their correspondence with the British abolitionist Granville Sharp and with John Wesley, the father of Methodism, Woolman and Benezet also helped to build the strength of the growing international antislavery movement. After reading Benezet's work, Wesley wrote in his journal, "I read a very different book, published by an honest Quaker, on that execrable sum of all villanies, commonly called the Slave-trade." That Wesley absorbed aspects of American antislavery thought is clearly reflected in Thoughts Upon Slavery (1774), a passionate tract that also reflects the mutually reinforcing links between secular and religious antislavery. For example, though he was a clergyman, Wesley sometimes wrote about antislavery in terms of rights and liberties: "Liberty is the right of every human creature, as soon as he breathes the vital air; and no human law can deprive him of that right which he derives from the law of nature."

　　The redefinition and expansion of antislavery proceeded in fits and starts through the 1760s. Benjamin Franklin and Adam Smith added another brick to the emerging intellectual structure of antislavery thought by depicting slavery as an outmoded form of labor destined for oblivion in a free-market world. Franklin's Observations Concerning the Increase of Mankind (1751) questioned slavery on practical rather than moral grounds, especially for its impact on white society: ". . .white children become proud, disgusted with Labour, and being educated in Idleness, are rendered unfit to get a living by Industry." Under the influence of his friend Anthony Benezet, Franklin's antislavery conscience gradually evolved by the 1770s. But it was the intriguingly strange James Otis whose intellectual originality brought the secular antislavery argument into sharper focus. In one of the first colonial attacks on slavery, The Rights of the British Colonies Asserted and Proved (1764), Otis deliberately grounded his objections to slavery in natural rights: "The colonists are by the law of nature free born, as indeed all men are, white or black. . . ."

　　Slavery came to the fore as an issue during the Stamp Act crisis as American colonists sought to distinguish themselves from Britain by employing the metaphor of slavery to describe political enslavement. The purpose was to enlist sympathy for colonial sufferings caused by British policies. But the trope opened up questions of liberty and freedom, and forced a rethinking of fundamental political concepts of slavery and freedom. The inconsistency, not to say hypocrisy, of slaveowners' complaints of being enslaved by King and Parliament was not lost on enslaved people. In their 1773 petition to the Massachusetts assembly, Peter Bestes, Sambo Freeman, Felix Holbrook, and Chester Joie seized upon the absurdity: "The efforts made by the legislative [sic] of this province in their last sessions to free themselves from slavery, gave us, who are in that deplorable state, a high degree of satisfaction. . . ." The convergence of spiritual and secular liberation is powerfully present in the petitions of Northern blacks, in sermons, and essays by black intellectuals like Jupiter Hammon and Prince Hall, in the poetry of Phillis Wheatley, and in the judicial pleadings of Elizabeth [Mum Bett] Freeman and Quock Walker. Enslaved men and women persistently asked nagging questions: "How can the master be said to Beare my Borden when he Beares me down with the. . .chanes of slavery?" "Is it consistent with the present claims of the United States to hold so many thousands of the race of Adam, our common father, in perpetual slavery?" In combining Christian morality and Anglo-American notions of right, black antislavery men and women constructed a compelling moral vision with a unique transforming potential. Their stress on the natural right of enslaved people to freedom as a fundamental human right universalized the revolutionary principles of liberty and equality: "We have in common with all other men a naturel [sic] right to our freedoms. . . ."