My parents assured me that to have the second sight one must be the seventh child of a seventh child.
I got a good deal of Irish tradition from my parents, but I couldn't tell you if it came from their parents, or from the Irish maids their parents employed.
My mother always said her grandmother was "fey". It was only shortly before she died that she would admit to being "fey" herself. I call it the whatsis, being reluctant to have that much faith in it. There was the time I got a strong sense not to walk down a certain street. I did. Two boys were tossing a football back and forth, and one of them got me good, right on the head. A three day headache!!! Since which time, if the whatsis says, don't go that way, I don't. but I refuse to take it really seriously.