In 1771 the periodical Éphémérides du citoyen (vol. VI) published a summary with lengthy excerpts of Ziméo (1769), a conte philosophique by Jean-François de Saint-Lambert. In his introduction Pierre Samuel Du Pont de Nemours described it as a “touching and warm poem based on a historical ground providing an accurate idea about these Negroes whom we debase with shameful and cruel shackles.” Saint-Lambert intended to prove that, once liberated from slavery, Blacks would be able to attain the same moral virtues and intellectual qualities as Whites. However, denouncing the injustice of Black slavery in the American colonies was not the only goal of the publication of Ziméo in the Éphémérides du citoyen: “this story,” continued Du Pont, does not only “show to what extent slavery is odious, it gives us also the opportunity to develop a calculation by which we are honoured to prove that, furthermore, this crime is useless and onerous for us.” Du Pont aimed at demonstrating that slavery was an anti-economic institution, not only a morally reprehensible one.

Calcul and morale were the key-elements of a debate which, from the last decades of the 18^th century up to the mid-19^th century, opposed French abolitionists to their adversaries (for and foremost the plantation owners) arguing in favour of a continuation of Black slavery in the colonies. This argumentative scheme, in which interest corroborated ethics, is at the centre of Calcul et morale. Coûts de l’esclavage et valeur de l’émancipation (XVIII ^e-XIX ^esiècle) (“Calculation and moral. The costs of slavery and the value of emancipation, 18^th-19^th c.”). This important book is the result of the fruitful collaboration between a historian of slave societies in the French Caribbean, Caroline Oudin-Bastide, and a sociologist specialised in the analysis of economic thought, Philippe Steiner. In nine chapters the authors examine the major writings of the French economists and politicians who took part in this debate. Hence, the book is essentially a study in the history of ideas. It focuses in particular on the conception that slave labour is more expensive than free labour and the productivity of a servile workforce is inferior to that of free workers.

It was precisely Du Pont who introduced this argument, first when introducing Ziméo and later in two articles published in the Éphémérides du citoyen (respectively in vol. VIII and XII in 1771). Significantly Oudin-Bastide and Steiner devote the first chapter to Du Pont, whose calculations constitute a sort of benchmark for the positions they examine in the other chapters. Moreover, the authors further highlight the importance of Du Pont’s writings by publishing two original pieces by him, nearly integrally [255-276].

So, what about numbers? Du Pont argues that a slave costs his master 420 livres a year, a large sum which includes: the purchase of the slave [120], the purchase of a new one to substitute him when he dies [120], his subsistence [100], the salary of the “half-hangman” (demi-bourreau, i.e. the slave driver) charged with flogging the slaves to make them work [42], and the defence of the plantations from the maroon communities [28]. The 420 livres were clearly a much higher sum compared to the annual salary of a European worker, which was estimated at about 30 livres. Moreover, Du Pont reckoned that the productivity of a slave was just half that of a free worker.

Oustin-Bastide and Steiner claim that Du Pont’s calculations, establishing that economic interest coincided with moral justice, were a decisive factor in the debates of the 18^th-19^th century. The institution of slavery was both inhuman and contrary to the interests of the planters and of the nation, as it impacted negatively the profits of plantation owners as well as the productivity of the colonies. The persistence of this institution was thus only due to the ignorance of the general interest. The “computing rhetoric” served two purposes: on the one hand, it refuted the idea that maintaining slavery was the only way to run a profitable colonial economy and for conserving the colonial system itself; on the other hand, it was meant to prove that a moral conduct would have sustained the interest of everybody (of the masters, the slaves and the entire nation). However, as contemporary observers already highlighted, Du Pont’s calculations were built on a fragile basis: they were criticized both by advocates of slavery and by his fellow abolitionist economists. Turgot, for example, considered that Du Pont’s calculations relied on arbitrary numbers and that thinking that slavery was not profitable to the slave owners was misleading. For Turgot, morality was the only legitimate basis of an anti-slavery position.

Oudin-Bastide and Steiner analyse the positions of Condorcet—who was convinced that abolition would both damage the interests of the planters and serve the interests of the nation—, other members of the Société des amis des Noirs, and first rank economists and politicians engaged in the abolitionist battle during the Restauration, the July Monarchy and the second Republic of 1848, which culminated in the final abolition of slavery in the French colonies. The list of authors reviewed in this way includes Comte, Dufau, de Broglie, Say, Sismondi, Tocqueville and Schœlcher, who tried to find a balance between calcul and morale and to develop solutions for overcoming slavery.

Calcul et morale is an interesting book. Although French anti-slavery ideas have been examined in various previous works, this monograph clearly contributes to a deeper and more comprehensive understanding of this movement. The analytical focus of Oudin-Bastide and Steiner’s work is on the texts. The changing socio-political contexts in which these texts were produced, or the transnational circulation of antislavery ideas—which would have connected the French debates in a very decisive way to Great Britain, but also to other states in continental Europe and to the Americas—receive rather marginal attention. But this critical remark does not belittle the value of this important book, which will certainly attract the interest of both students and specialists.