The concept of person was further developed during the Trinitarian and Christological debates of the 4th and 5th centuries in contrast to the word nature. During the theological debates, some philosophical tools (concepts) were needed so that the debates could be held on common basis to all theological schools. The purpose of the debate was to establish the relation, similarities and differences between the /"Verbum" and God. The philosophical concept of person arose, taking the word "prosopon" () from the Greek theatre. Therefore, Christus (the /"Verbum") and God were defined as different "persons". This concept was applied later to the Holy Ghost, the angels and to all human beings.