A mononymous person is an individual who is known and addressed by a mononym, or "single name". In some cases, that name has been selected by the individual, who may have originally been given a polynym ("multiple name"). In other cases, it has been determined by the custom of the country or by some interested segment. In the case of historical figures, it may be the only one of the individual's names that has survived and is still known today.
The structure of persons' names has varied across time and geography. In some communities, individuals have been mononymous, receiving only a single name. Alulim, first king of Sumer, is one of the earliest names known; Narmer, an ancient Egyptian pharaoh, is another. Later, Biblical names were typically mononymous, as were names in the surrounding cultures of the Fertile Crescent. Ancient Greek names also follow the pattern, with second names only used to avoid confusion, as in the case of Zeno the Stoic and Zeno of Elea; patronymics or other biographic details (such as city of origin, or another city the individual was associated with, borough, occupation) were used to specify whom one was talking about, but these details were not considered part of the name.
A person is a being, such as a human, that has certain capacities or attributes constituting personhood, which in turn is defined differently by different authors in different disciplines, and by different cultures in different times and places. In ancient Rome, the word persona (Latin) or prosopon (πρόσωπον; Greek) originally referred to the masks worn by actors on stage. The various masks represented the various "personae" in the stage play.
The concept of person was 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 Λóγος/Verbum and God. The philosophical concept of person arose, taking the word "prosopon" (πρόσωπον) from the Greek theatre. Therefore, Christus (the Λóγος/Verbum) and God were defined as different "persons". This concept was applied later to the Holy Ghost, the angels and to all human beings.
Grammatical person, in linguistics, is the grammatical distinction between deictic references to participant(s) in an event; typically the distinction is between the speaker, the addressee, and others. Grammatical person typically defines a language's set of personal pronouns. It also frequently affects verbs, sometimes nouns, and possessive relationships.
In Indo-European languages, first-, second-, and third-person pronouns are typically also marked for singular and plural forms, and sometimes dual form as well (grammatical number). Some languages, especially European ones, distinguish degrees of formality and informality (T-V distinction).
Some other languages use different classifying systems, especially in the plural pronouns. One frequently found difference not present in most Indo-European languages is a contrast between inclusive and exclusive "we": a distinction of first-person plural pronouns between including or excluding the addressee.
In the canon law of the Catholic Church, a person is a subject of certain legal rights and obligations.
The age of reason is the age at which children attain the use of reason and begin to have moral responsibility. On completion of the seventh year a minor is presumed to have the use of reason, but mental retardation or insanity prevent some individuals from ever attaining the use of reason. The term "use of reason" appears in the Code of Canon Law 17 times, but "age of reason" does not appear. However, the term "age of reason" is used in canon law commentaries such as the New Commentary on the Code of Canon Law published by Paulist Press in 2002.
Children who do not have the use of reason and the mentally handicapped are sometimes called "innocents" because of their inability to commit sins: even if their actions are objectively sinful, they sometimes lack capacity for subjective guilt.
In the Eastern Catholic Churches, the Eucharist and Confirmation are given immediately after baptism, even to infants who do not yet have the use of reason. In Latin Rite Catholicism, Confirmation is conferred, except in danger of death, only on persons who have the use of reason; and Holy Communion may be administered to children only if "they have sufficient knowledge and careful preparation so that they understand the mystery of Christ according to their capacity and are able to receive the Body of Christ with faith and devotion." In danger of death, the Eucharist may be administered also to children who lack the use of reason, if the child can distinguish the sacrament from ordinary food and receive it reverently. This is likewise true for those who are not so mentally retarded that they are not assumed to ever gain use of reason.