I never could keep cousins straight.  First cousins—the children of my parents' siblings—I understood, but I was lost when it came to second and third cousins, let alone those with the "removed" designation.  Not that I cared; it was rarely an issue for me.  When genealogy entered my life, however, family relationships suddenly needed to be a whole lot more specific.

After much puzzing over confusing definitions and tables, I gained enough head-knowledge to create the following algorithm.  My gut instincts in the matter are still a bit fuzzy, so I fall back on the strategy of the confused high school algebra student and rely on formulas.

To Calculate the Family Relationship Between Person A and Person B

Find C, the common ancestor between A and B.

Let N = the number of generations from A to C

Let M = the number of generations from B to C.

  1. If N = 0, A is the (M – 2)th great grandparent of B, where the 0th great grandparent is defined as “grandparent,” the –1st great grandparent is defined as “parent,” and the –2nd great grandparent is defined as “self.”
  2. If M = 0, A is the (N – 2)th great grandchild of B, where the 0th great grandchild is defined as “grandchild,” the –1st great grandchild is defined as “child,” and the –2nd great grandchild is defined as “self.”
  3. If N = 1 and M > 0, then A is B’s (M – 3)th great grandaunt/uncle, where the 0th great grandaunt/uncle is defined as “grandaunt/uncle,” the –1st great grandaunt/uncle is defined as “aunt/uncle” and the –2nd great grandaunt/uncle is defined as “sister/brother.”
  4. If M = 1 and N > 0, then A is B’s (N – 3)th great grandniece/nephew, where the 0th great grandniece/nephew is defined as “grandniece/nephew,” the –1st great grandniece/nephew is defined as “niece/nephew” and the –2nd great grandniece/nephew is defined as “sister/brother.”
  5. If N > 1, M > 1, and N = M, then A and B are (N – 1)th cousins.
  6. If N > 1, M > 1, and N < M, then A and B are (N – 1)th cousins, M – N times removed.
  7. If N > 1, M > 1, and N > M, then A and B are (M – 1)th cousins, N – M times removed.
It's a little nerdy—okay it's a lot nerdy—but it works for me, and I've never seen anything like it, so I post it here in case it may help someone else.
Posted by sursumcorda on Tuesday, June 9, 2009 at 9:26 am | Edit
Permalink | Read 2073 times
Category Genealogy: [first] [previous] [next] [newest]
Comments

Wow! Brother Rich did our family genealogy and explained it all, but he's a materials science person, not a computer nerd or mathematician, so used different words! "x cousin" means same generation as each other, whether first or second or third; "once removed" refers to the two people being in different generations from each other - once is one generation below, twice is two generations (e.g. the grandchild of a cousin.) What a mind you have!

There, now I've done it!



Posted by Laurie on Tuesday, June 09, 2009 at 8:10 pm

I'm very impressed and honored! Come back anytime. :)



Posted by SursumCorda on Tuesday, June 09, 2009 at 10:17 pm

I submit a correction (still in proofreading mode):

1. If N = 0, A is the (M – 2)th great grandparent of B, where the 0th great grandparent is defined as “grandparent,” the –1st great grandparent is defined as “parent,” and the –2nd great grandparent is defined as “self.”



Posted by Stephan on Wednesday, June 10, 2009 at 9:48 am

Thank you. Definitely a cut-and-paste malfunction!



Posted by SursumCorda on Wednesday, June 10, 2009 at 10:31 am
Add comment

(Comments may be delayed by moderation.)