While Sen’s ethics, particularly through his capability approach, are recognised for their critical nature and alignment with certain realist ontological principles, this paper explores the compatibility and potential tensions between Sen’s framework and Critical Ethical Naturalism (CEN), an ethical theory introduced by Tony Lawson. This comparative exercise reveals that Sen’s adoption of realist ontological notions such as openness, relationality and the importance of process and institutions suggests compatibility with CEN—a potential compatibility noted by Lawson himself. However, there is also an important difference between Sen’s moral theory and CEN, which indicates the possibility of further fundamental tensions between them. This difference lies in their divergent orientations regarding the content and relevance of ontology. Sen’s project is shown to be predicated on the irrelevance of ontology to ethical theorising, which contrasts sharply with Lawson’s framework; indeed, the whole point of Lawson’s approach is to develop an ethical theory grounded on an explicit ontological account. Through a detailed examination of Sen’s reluctance to engage with ontology, an exploration of potential sources of this reticence and an analysis of the explicit ontological basis of CEN, the paper highlights fundamental distinctions between Sen’s approach and CEN.