He warmly praised the ministry of "Black Harry" Hosier, the freedman circuit rider who accompanied Bishop Francis Asbury during the establishment of the Methodist Church in America, but the highlight of his involvement was the pamphlet he wrote in 1773 entitled "An Address to the Inhabitants of the British Settlements in America, upon Slave-Keeping." In this first of his many attacks on the social evils of his day, he assailed the slave trade as well as the entire institution of slavery. Rush argued scientifically that Negroes were not by nature intellectually or morally inferior. Any apparent evidence to the contrary was only the perverted expression of slavery, which "is so foreign to the human mind, that the moral faculties, as well as those of the understanding are debased, and rendered torpid by it."