You may have been at a family reunion or gathering and heard someone trying to figure out how two of the participants were related. It may have been obvious that they were cousins, but were they third or fourth cousins, and how far (and why) were they removed from each other?

What they were attempting to describe is how closely they were related, without having to name all of the ancestors between each of them and their Common Progenitor (the CP is the most recent ancestor both persons share). This method is referred to as determining their common (or canon) law relationship, which can be easily done with the aid of a relationship chart such as the following:

CP = Common Progenitor

B = Brother or Sister

S = Son or Daughter

N = Nephew or Niece

C = Cousin

1C = First Cousin

GS = Grandson or Granddaughter

GGS = Great Grandson or Great Granddaughter

2GGS = 2nd Great Grandson or 2nd Great Granddaughter

GN = Grandnephew or Grandniece

GGN = Great Grandnephew or Great Grandniece

2GGN = 2nd Great Grandnephew or 2nd Great Grandniece

R = Times Removed

3C 2R = Third Cousins twice removed

The cells in the top two rows and left two columns are bolded to indicate that they refer to the Common Progenitor (CP) and his/her descendants. The persons referred to in these bolded cells are the direct descendants of the CP. The other cells (non-bold) in the chart are used to determine the relationship between two descendants of the CP.

For example, Mark Tharret and Michael V. Grobbel once both worked in the same engineering department at General Motors. They knew they were related, but couldn’t easily describe how close their relationship was.

From the Anton Grobbel Descendant Chart, they uncovered that they shared the same great-great-grandfather (Anton Grobbel ₁₅). With the information about their common ancestor and his descendants, they used the Common Law Relationship Chart to figure out what kind of cousins they are. Down the left side of the Relationship Chart, Anton Grobbel ₁₅ (the CP or Common Progenitor) was 0, Anthony Grobbel ₁₆ was 1, Clement Grobbel ₁₇ was 2, Vincent Grobbel ₁₈ was 3 and Michael Grobbel ₁₉ was 4. Across the top, Anton Grobbel ₁₅ (CP) was 0, Bernard Grobbel ₁₆ was 1, Martina Grobbel ₁₇ was 2, Arlene Vohs ₁₈ was 3 and Mark Tharret ₁₉ was 4. The cell at the intersection of Row 4 and Column 4 is labelled "3C", which indicates that Mark Tharret and Michael Grobbel are third cousins.

To determine the degree of "cousinhood" without a relationship chart, simply count the number of generations between you and the Common Progenitor, and then subtract one. Since Mark and Michael are each from the 19th generation and their CP is 15th generation, ((19 - 15) - 1) = 3, indicating that they are third cousins. The part about being "removed" is to show the difference (if any) in the number of generations between the two persons and the CP. So if one person counts back five generations to the CP, while the other counts back four generations, the difference is one generation, resulting in the determination that they are "once removed". In these cases, the smallest degree of "cousinhood" is used, so that these two people are third cousins once removed, not fourth cousins once removed. The relationship between Mark Tharret ₁₉ and Phillip Grobbel ₂₀ (son of Michael) is that of third cousins once removed.