Within modernity canonical philosophers were deeply engaged in debates surrounding both the expansion of slavery and its subsequent abolition, but historians of political philosophy tend to ignore their contributions. In this paper I focus on one of the most prevalent arguments: the claim that prisoners captured in war can legitimately be enslaved. This provides the context for raising the broader questions of why within academic philosophy the positions adopted by canonical philosophers on slavery continue to be treated as of only marginal interest and of how changing this could have major implications for debates about  the philosophical canon.