With the edition, translation and study of a 16th century moral theology treatise, Maria Madalena Brito shows how this discipline was the area par excellence for critical debate on slavery in Portugal at this time. This was substantial in comparison with what occurred in other areas of Portuguese culture. Any questioning of slavery then involved enormous theoretical and practical complexity as there was a conflict between what was ideal at the level of conscience and what was felt at the time as a condition for the economic prosperity of an entire empire. Neither Fernão Pérez nor other Professors in Portugal condemned slavery in absolute terms. However, Pérez and other theologians approached sensitive subjects, suggesting the limitation of slave trade, denouncing situations of injustice and violence towards the slave, demanding restitution of freedom to slaves who were not so by just title. They stressed the humanity of the slave based on their Christian conscience and on classical principles of natural law.