The research presented here aims to show how competing views of slavery in the Catholic Atlantic were debated, reinforced, and at times challenged the legal and moral foundations of the transatlantic slave trade. The intellectual inspiration for this note comes from a close engagement with John K. Thornton’s discussion of African political ethics and the slave trade, and L.F. de Alencastro’s analysis of competing Portuguese visions on the slave trade. My research is an attempt to bridge the gap between Iberian and Kongolese views of slavery to illustrate that even at the time, legal and moral justifications and objections arose from both sides.