  The influence of Augustine in the subsequent history of ethics resulted from the fact that it was his synthesis of Christianity (the official religion of the Roman Empire after 325) and Greek philosophy that survived the destruction of the Western Roman Empire, especially in the monasteries where the texts were still read. Boethius (c. 480–524) gave us the definition of the concept of ‘person’ that has been fundamental to ethical theory. To understand this, we need to go back into the history of the development of the doctrine of the Trinity. The church had to explain how the Father, the Son and the Holy Spirit could be distinct and yet not three different gods. They used, in Latin, the term persona, which means ‘role’ but which was also used by the grammarians to distinguish what we call ‘first person, second person and third person’ pronouns and verb-forms. The same human being can be first person ‘I’, second person ‘you’, and third person ‘he’ or ‘she’, depending on the relations in which he or she stands. The doctrine of the Trinity comes to be understood in terms of three persons, one God, with the persons standing in different relations to each other. But then this term ‘person’ is also used to understand the relation of the second person's divinity to his humanity. The church came to talk about one person with two natures, the person standing under the natures. This had the merit of not making either the humanity or the divinity less essential to who Jesus was. Plato and Aristotle did not have any term that we can translate ‘person’ in the modern sense, as someone (as opposed to something) that stands under all his or her attributes. Boethius, however, defines ‘person’ as ‘individual substance of rational nature,’ a key step in the introduction of our present concept.