<P> This sometimes originates as a simple patronym--that is, a James whose father was Harry might be referred to as Harry's James--but may be passed to later generations, so that James' son Pat might be Harry's Pat . This can also occur if a person becomes well known by a nickname: his children may take his nickname as an additive . For example, if Seán O'Brien was often referred to as "Badger", his son Patrick might be referred to orally as Pat Badger and written as Patrick O'Brien (B). </P> <P> In Tipperary, additives are particularly common among those bearing the Ryan surname . Examples include Ryan Lacken, Ryan Luke and Ryan Doc . A man christened Thomas Ryan might be known as Tommy Doc and his family might be referred as the Docs . While the additive is not part of a person's official name, it may be used in a postal address, on an election register or in newspaper reports . In this case, Tommy Doc might be written as Thomas Ryan (D). </P> <P> In Gaeltacht (Irish - speaking) areas, it remains customary to use a name composed of the first name, followed by the father's name in the genitive case, followed by the name of the paternal grandfather, also in the genitive . Thus Seán Ó Cathasaigh (Seán O'Casey), son of Pól, son of Séamus, would be known to his neighbours as Seán Phóil Shéamuis . Occasionally, if the mother or grandmother was a well - known person locally, her name may be used instead of that of the father or grandfather . If the mother's name is used, then that of the maternal grandfather (or potentially grandmother) follows it, for example, Máire Sally Eoghain . </P> <P> These names are not used for official purposes . Often a nickname or English version of a name is used in their composition where the person would use a standard Irish form in formal circumstances . For example, the prominent sean - nós singer Seán Mac Dhonnchadha is perhaps better known as Johnny Mhairtín Learaí . </P>

Why do the irish have o in their names