What’s up with Dad?

My father was always Pop. He was born in 1908. His father, also Pop, was born in 1863. That guy’s father was born in 1809, and I don’t know what his kids called him. I’m guessing, from the chart above, it was Pa. My New Jersey cousins called their father Pop. Uncles and their male contemporaries of the same generation in North Carolina, however, were Dad or Daddy.

To my kids, I’m Pop or Papa. Family thing, again.

Anyway, I’m wondering what’s up, or why’s up, with Dad?