Kinship is the bond that unites people who descend from the same common ancestor, technically called the “root” (stipite). In the legal sphere, this bond is recognized and produces legal effects only up to the sixth degree. Beyond this limit, despite a blood tie existing, the law no longer considers the people as relatives. Understanding how these degrees are calculated is essential both for genealogical research and for matters of inheritance or civil law.
To determine the degree of kinship, one must count the generational “steps” that separate two people. The common ancestor (stipite), meaning the ancestor from whom the group descends, is the point of reference but is never counted in the final calculation. Depending on the type of bond, kinship is divided into two categories: direct line and collateral line.
The direct line unites people who descend from one another, as in the case of parents and children or grandparents and grandchildren. To calculate the degree, you simply count the steps between generations. For example, between you and your father there is only one step, so you are first-degree relatives. Between you and your grandfather there are two steps, making you second-degree relatives. A great-grandfather represents the fourth generation of the family if we include you, but the kinship bond is of the third degree because the steps needed to reach him starting from you are three.
The collateral line, on the other hand, concerns people who, despite having a common ancestor, do not descend from one another. This is the case with siblings, aunts/uncles, and cousins. To calculate the degree in this line, you must “go up” to the common ancestor and then “go down” to the relative in question, counting every step.
A common mistake concerns the bond between siblings. Since siblings do not descend from one another, to calculate their kinship you must go up to the parent (+1) and go down to the sibling (+1). The total is two, which means siblings are second-degree relatives. There is no first-degree kinship in the collateral line, as the first degree is reserved exclusively for the direct relationship between parent and child.
Following the same pattern, you can calculate the degrees for more distant relatives like aunts/uncles and cousins. To reach a cousin, you must go up to the grandfather (the common ancestor) and then go down through the aunt/uncle to the latter’s child. This path involves four steps: from you to your father, from your father to your grandfather, from your grandfather to your aunt, and from your aunt to your cousin. Therefore, those we call “first cousins” in everyday language are, under Italian law, fourth-degree relatives.
