As David Eltis has recently emphasised, the Portuguese dominated the Atlantic slave trade from its inception to its close, except for a British interlude between 1730 and 1800 (Atlantic cataclysm: rethinking the Atlantic slave trades, Cambridge 2025, ch. iv). Understandably, the trade in enslaved Africans provoked debate among Iberia’s moral theologians, notably the Portuguese Jesuit, Fernão Pérez. In The slave is a human person, Maria Brito has transcribed two of his Latin manuscripts – De restitutione (1588) and a shorter text ‘On the acquisition of domination over human beings’. This would be a significant intervention in its own right, but the book also includes a full English translation, extensive annotations, and a monograph wrapped around the original texts with four substantial chapters: ‘Pérez’s biography’, ‘Intellectual-historical framework’, ‘Analysis of Pérez’s De restitutione’, and ‘Final observations’.

It is difficult to do justice to this rich work in a short review. It makes an important contribution to the literature on what Brito calls ‘the Iberian Scholastic School’, what is often known as ‘Second Scholasticism’, including ‘the School of Salamanca’. It will appeal to intellectual historians, legal theorists and moral theologians, as well as scholars concerned with Atlantic slavery. Brito admits that Pérez is ‘practically unknown, even within legal history’ (p. xv), largely because he resisted the clamour to publish his writings. Yet in his own day he was a revered figure, consulted by the Portuguese elite on cases of conscience. Here he emerges from under the shadow of his successor, Luis de Molina, whose famous treatise on God’s ‘middle knowledge’ was published only after Pérez had reviewed it for the Jesuit order.

Brito argues that Pérez is ‘at the beginning of the tradition of theological and legal reflection on dominion and slavery’ (p. xv). So how did he think about slavery and the African slave trade? He acknowledges Aristotle’s concept of ‘natural’ slavery, but does not apply it to the enslavement of Africans, or develop a racial defence of the Atlantic slave trade. Instead, he focuses on ‘legal’ slavery (what Julia Jorati has labelled ‘circumstantial’ slavery). He takes it for granted that slavery can be legitimate – this is the verdict of the Western intellectual tradition and of Scripture, and it would be ‘heresy’ to deny it (p. 188). Although human persons are free under the law of nature (whereby ‘all things belong to everyone’), they can be enslaved under the the law of nations (whereby things are divided and property is created). However, the power of masters over slaves is strictly limited ‘to services reasonably required’ (p. 189), and slaves retain a right to marriage, the sacraments and their own bodily integrity. Pérez identifies four legitimate ways in which a person may be enslaved (what Brito calls ‘the four classical titles of slavery’): by birth (to an enslaved mother), by consent (in cases of extreme necessity), by crime, and by ‘the crime of fighting an unjust war’ (p. 202). But have enslaved Africans been ‘justly enslaved’ in one of these ways? Pérez acknowledges that they may have been illegally captured, and he emphasises that to knowingly purchase such slaves in bad faith is a mortal sin. Christian merchants on the west African coast thus have a duty to do ‘due diligence’ and investigate whether Africans have been ‘unjustly enslaved’ (pp. 198–9, 228–9). However, this duty does not apply to Christians who buy slaves in Lisbon – they have to assume that the Christian slave traders who made the original purchase did so ‘in good faith’ and ‘proceeded with due diligence’ (pp. 200, 229).

Brito’s analysis accentuates the positive: Pérez stresses the odious and unnatural character of slavery and the humanity of the slave; he avoids any doctrine of natural slavery based on race; he condemns illicit forms of capture and enslavement practised by Africans and Portuguese alike; he demands due diligence and restitution in cases of illegal slavery; he rules out evangelisation as a rationale for slave trading; he underscores the limits of the power of masters; he defends the rights of the slave. At a time when ‘the majority of intellectuals’ were ‘conspicuously silent on the ethical problems of slavery’ (p. 344), Pérez addressed the subject directly, and sought to restrain, humanise and moralise the institution. At the same time, Brito concedes that Pérez was naïve to trust in ‘the concern of the Portuguese Crown for the justice of the titles and the Christian conscience of the merchants’ (p. 317). Few slave traders were scrupulous, and neither were their African counterparts. The missionary Baltasar Barreira reported that African traders found it ‘laughable’ when Europeans enquired about the justice of their ‘title’ to slaves (p. 319). The casuist’s insistence on due diligence, in other words, proved a dead letter. Portuguese merchants typically claimed that enslaved Africans were better off (materially and spiritually) in the hands of Europeans. The jurisprudential category of ‘just slavery’ provided a pretext for European slave trading, rather than a check to it. Eventually, in the abolitionist era, a growing number of Christians would come to embrace what Pérez considered heresy: the claim that slavery per se was unjustifiable. Before 1700, however, this thought was almost unthinkable.

The slave is a human person is essential reading for anyone who seeks to understand Christian thinking on slavery before the rise of abolitionism. It can be read alongside Jorati’s valuable survey, Slavery and race: philosophical debates in the sixteenth and seventeenth centuries (Oxford 2024). And it will interest anyone concerned with the natural law tradition, early modern scholasticism, Jesuit casuistry or the Iberian theojurists. There is the occasional typo (one extending the lifespan of John Stuart Mill to 1973, a counterfactual that will delight some readers). A paragraph on pp. 240–1 is printed twice. These are very minor flaws in what is a most impressive and engrossing book.