The Introduction outlines the aims and structure of the book. It begins by situating the Cambridge Social Ontology (CSO) project within the Cambridge tradition and outlining its critique of mainstream economics. It then presents the two central components of CSO, Social Positioning Theory (SPT) and Critical Ethical Naturalism (CEN), as complementary accounts of the social and ethical constitution of human life. Attention is given to the ethical and political dimensions of SPT and to the way CEN provides its ontological and moral grounding. The discussion further examines CEN’s Aristotelian roots and its potential to offer a coherent alternative to dominant moral frameworks. The final section introduces the comparative focus of the book, which explores the relationship between CSO and Amartya Sen’s contributions to political economy and ethics. Together, these sections establish the theoretical and methodological basis for the analysis that follows and clarify the importance of ontological consistency for reviving political economy as a comprehensive social science.