The O'Dwyer Clan Newsletter (Spring 2015) included an article entitled "Find your Irish roots through family naming patterns" written by Stephanie Varney. Here's a portion of her article: Nineteenth-century Irish family naming patterns usually follow the guidelines in the list below pretty closely.

1. The eldest son was named after the father's father.
2. The eldest daughter was named after the mother's mother.
3. The second son was named after the mother's father.
4. The third son was named after the father.
5. The fourth son was named after the father's oldest brother.
6. The second daughter was named after the father's mother.
7. The third daughter was named after the mother.
8. The fourth daughter was named after the mother's oldest sister.

...for example, if you're looking for the parents of an Irish ancestor named Michael Donnahue, and you know Michael's first-born son was named Martin, then this might be a clue that Michael's father's name was also Martin. In this case, you can look more closely at men by the name of Martin Donnahue who lived in the same area as Michael and were of the right age to be Michael's father. Knowing the traditional naming patterns helps you find your Irish roots by alerting you to clues of identifies you may have otherwise missed... While I was aware that first names could be a clue to family relationships, I'd forgotten about the naming convention for the fourth son/daughter. Upon further googling, I found a rule about a fifth-born child, namely a son would be named after the mother's oldest brother or a daughter named after the father's oldest sister. In another source I found that a second wife's oldest daughter would be named after the first wife. I also read the convention was modified if it resulted in three people in the family having the same name. There's apparently an old superstition that if three people have the same name, one would die. Another reason the rules were not followed was if, as an example, both grandfathers had the same first name. My husband Bill's great-grandparents, Patrick and Julia (Ryan) Hickey, had nine children. Their names and birthdates are recorded in the family Bible. Here they are listed in birth order by gender: Daughters:

1. Mary  (b 1857)
2. Margaret (b 1858)
3. Honora "Annie" (b 1862)
4. Julia (twin born 1865)
5. Ellen "Nell" (born 1869)

Sons:

1. James (b 1860)
2. Patrick (twin born 1865)
3. William (born 1866)
4. Michael (born 1871)

The naming convention was not consistently applied in this family, just enough to be confounding:

• Patrick's parents were James and Margaret Hickey (correctly predicted by children's names).
• We believe Julia's parents were William and Annie Ryan (but the names were passed on to third-born son and daughter).
• So why was the first daughter named Mary? (Her full name was Mary Josephine.)
• Did the birth of twins prompt the parents to pass on their own names (Patrick and Julia) without regard to the regular naming pattern?
• (Father) Patrick's oldest brother was, in fact, named Michael.
• Did Julia have a sister named Ellen or Nell? Patrick had a younger sister named Nelly who we think died as a child while the family was still in Ireland.

One thing is for certain: the naming patterns ensured that the same names would appear generation after generation - to confuse researchers as much as help them.