The ontology of the last chapter divided human nature and selfhood into branching layers with a variety of sources. We are composites of soul and body, of forms and a material aspect organised by forms. The relation between individual rational subjectivity and the composite person with both a body and living functions is problematic. Furthermore, embodied selves are temporal creatures whose existence extends in time. Their identity is threatened, in that they never exist ‘all at once’, but with past and future horizons, or even parts. The self seems to be split into two radically different kinds of beings: unchanging and unified immortal souls or intellects and divided as well as multifaceted temporal and material composites. Yet every self and subject is also one: human beings are individuals, in that they exist as determinate beings in one body both at a time and through time. According to the simplest explanation, it is the soul and its formal power that gives human individuals their unity. As a non-spatial principle of organisation, it is by definition a principle of unity, too. So far, however, the organisation and unity endowed by such a principle to the composite has been mostly material: it is the structure of the extended thing as well as the future constitution of living things. But human beings are not just well-organised material bodies or even beautiful plant-like things with organised growth and lifespan. They move in co-ordinated ways and they experience themselves as unified centres of experience.