How Do Cousins Work?
If you’re like me, you probably always found the whole “second cousin twice removed” thing difficult to figure out. So, I thought, why not provide a document right here to help us all get a better handle on this. After all, if you’re a member of the O’Brien Clan website, then you’re DEEP in cousin territory.
So, cousins are people who share a common ancestor that is at least two generations away from them, like a grandparent or great-grandparent, but not a parent because that’s just one generation away from you.
Simple Cousins (without any “removeds”)
Let’s start simple and go on from there.
To be a cousin WITHOUT the addition of any “x removed” attached, you and the other person must share the SAME common ancestor at the SAME level. Let’s look at a few examples:
If you and the other person share the same grandparent, then you’re first cousins. This would be like me and Wendi Henkes, my Aunty Claire’s daughter, because Bill O’Brien is grandfather to both Wendi and me.
If you and the other person share the same great grandparent then you’re second cousins. This would be like me and my Mum’s cousin’s child. So, Tom Casey is my Mum’s cousin (he’s the son of Roy Casey, who’s Irene’s brother) and any child of Tom’s would be my second cousin. Let’s refer to this Tom as “Tom Casey Junior” to avoid confusing him with all the other “Toms”.
If you and the other person share the same great great grandparent then you’re third cousins. And at this stage it’s getting too hard for me to think of a live example, so let’s move on.
You’ll see that in the three examples above, the two people ALWAYS share the same “level” of ancestor, like grandparent or great grandparent or great great grandparent.
A TIP TO ASSIST - Here’s a great tip so you can easily figure out what level of cousin you and a relative are – remember that this only works if you’re both the same number of generations removed from the common ancestor (ie you’re both at the same “level”). You count how many “greats” are in your common ancestor’s title and add one and that will tell you what number cousin your relative is. Note that grandparents have no “greats” in their titles, so cousins who share grandparents are first cousins because 0 + 1 = 1. Those who share a common great great great grandparent would be 4th cousins.
I’m more of a “words” person, but I know a lot of people are far more “visual”, so here’s a good chart to help you get this all in perspective.
More Complex Cousins
The whole “twice removed” thing comes in when you and the other person share a common ancestor that’s at least two generations away from you, BUT they’re not at the same “level” for both of you, ie you’re NOT both the same number of generations removed from that common ancestor.
So, let’s look at few examples:
If my grandparent is the other person’s great grandparent, then we’re “once removed”. Because Wendi and I are first cousins, her daughter Sonya inherits that from that relationship, and because Bill is Sonya’s great grandfather and he’s my grandfather, that means we’re once removed, ie there’s one generation between the relationship I have with Bill and the relationship Sonya has with Bill. So, Sonya and I are “first cousins, once removed”.
Sonya’s son Remy would therefore be my first cousin (again inheriting that from the relationship between Wendi and me), twice removed (because Bill is my grandfather and Remy’s great great grandfather, so there’s two generations between my relationship with Bill and Remy’s).
In the example of Tom Casey Junior and me from the previous section, I was Tom Junior’s child’s second cousin, so a child of that second cousin would be my “second cousin, once removed”.
A TIP TO ASSIST - Your parent’s first, second, and third cousins are also your first, second, and third cousins - but once removed. This is because your parents and their generation are one generation above yours – the different levels is the thing that gives you the “removed” bit. Likewise, your grandparents’ first, second, and third cousins are also your first, second, and third cousins, but this time twice removed. This pattern continues throughout each generation.
An easy way to think of it is once you’re on an X numbered cousin’s path, providing there are NO “removeds”, any cousin above or below on that same path, will also be an X numbered cousin – they may just have one or more “removeds”. For example, all of the children, grandchildren, great grandchildren and onwards that my first cousin Wendi has will ALL be my first cousins, with each new level down adding one to the number of “removeds”.
But here’s an interesting twist. A first cousin once removed is either the child of your first cousin or the parent of your second cousin. WTF! It was probably all going quite well until that last sentence. That one probably messed with your head, and made it all too hard, AGAIN!
But think of it like this. My second cousin was Tom Casey Junior’s child. So, Tom Casey Junior is my Mum’s first cousin. That also makes him my first cousin, but since we’re not at the same “level” (ie Tom Casey Senior is Tom Casey Junior’s grandfather, but he’s my great grandfather), we’re once removed.
And since this is a little more complex, and to allow for more generations than the previous chart, here’s one that will help.
To work with this one, figure out what level of grandparents you and the other person share. On the X axis (top) find that level of grandparent for you, and on the Y axis (left hand side) find the level of grandparent for your cousin. Where they intersect is your relationship.
Taking Tom Casey Junior and me. Tom Casey Senior is Tom Casey Junior’s grandfather (left hand axis row 1), but he’s my great grandfather (top axis column 2), hence Tom and I are “first cousins once removed”.
And there it is. It’s as simple as that. I would suggest that you email me using the details on the contact page with any queries on this, but to be honest, I may be a bit busy that day.
Written by Rob Landsberry, last updated 18 May 2023
References:
https://www.familysearch.org/en/blog/cousin-chart
https://fh.familysearch.org/system/files/team/ait/images/blog/cousin-chart.pdf
https://fh.familysearch.org/system/files/team/ait/images/blog/cousin-calculator-2.jpg