I've found the naming pattern to be of great benefit in my own research. Yes, it's not always followed exactly - and I've noticed it to be less well adhered to for girls - but you should make it the initial, default assumption & that will help you in figuring out where to look to begin with.
So, if you know the names of the grandparents, you can search for children named after them. That said, it’s actually apparent deviations from the pattern that I’ve found to be the most fruitful avenue for investigation. The usual reasons are overlaps in names and premature deaths. What I mean by that is best illustrated by some examples, which have turned up a few times for me.
The pattern was: 1st son after husband's father, 2nd son after mother's father, 3rd son after father, possibly 4th son after father's oldest brother and so on. So, what does it mean if you notice that the children were not named in this order? Here are two possibilities:
- You don't know the names of the two grandfathers, but you notice that 2nd son has the same name as his father. That could mean either that the mother's father had the same name as the husband or as the husband's father.
- You look at a census record. Oldest son has the same name as the mother's father, next son has the father's name and it's the 3rd son who has the husband's father's name. What that might suggest is that there was an earlier child, named in the standard way, who died previously. The name (that of the husband’s father) was re-used for a subsequent son. You can now go looking for the death of a child – you have the name and some idea of when he died.
My own experience in County Down is that there was pretty strong adherence throughout the 19th Century, but it tailed off sharply once into the 20th.