A Classic Exchange, Literally

This exchange took place between Nancy and Karl, as Nancy searched for very specific information, as well as a little math help:

N: If David Hume, of the Scottish Enlightenment, was to be my grandfather
of yore (he's not), would he be my great, great, great grandfather?
Exactly how many greats would be included?

K: He never married so, at least legally, he's no one's grandfather. A trick question.

In general ...

You can't answer this kind of question in the abstract since you don't know how long any particular generation is. If, for example, he had a child who had a child when he was 16 who had a child when he was 17 ....or he could have had children who didn't have children until they were 30.

If we assume a generation is twenty years AND Hume had a line of descendants -- starting in 1731 when he was twenty AND each following generation had a child at 20 that would make his descendants now something like the 13th generation.

N: How old was James Madison in 1731?

K: He wasn't born until 1751 so the answer is O -- although in some Asian countries one is considered a year old at birth. This is further complicated by the fact that in England (and England colonies) until 1751 the legal year began on March 25 -- due to differences between the Gregorian and Julian calendars.