Where we find medieval distinctions between philosophy and theology, the term ‘philosophy’ describes the mode and degree the soul’s participation in the gracious revelation of God’s wisdom apart from – though ideally in cooperation with – the further means of grace which are manifest through the Church alone. This thesis explores what philosophy, thus defined, means in an early Irish context, and does this through an exploration of the way that nature is conceptualised in contrast to the realities and capacities taken to be manifest in the Church. Chapter 1 discusses the influence of Isidore’s parallel conceptions of natural law and natural language on the way that secular political hierarchies were conceived in early Irish literature. Chapter 2 shows that, in early Irish literature, natural law does not generally mean the vestigial capacity for ethics that remains to the soul after the Fall, as it does for the Latin Doctors, but the mode of inspiration by the Holy Spirit that is appropriate to the secular hierarchies. Chapters 3 and 4 concern contrasting positions on the degree to which this natural law can be politically relalised in the Christian Era. Chapter 3 outlines the influence of Eusebian triumphalism, which sees the Christian Era as the time in which the natural law may be most perfectly known. Chapter 4 discusses the influence of Augustine’s theory of the Six Ages of the World, which sees the Christian Era as less capable of embodying the natural law than former ages. Chapter 5 discusses the meaning of metamorphosis and metemphyschosis in an early Irish context, in view of their apparent incompatibility with Christian ideas concerning human nature. Chapter 6 shows that the gods of the early Irish sagas do not compromise the philosophical theology of nature discussed in the preceeding, but rather, are integral to it.