In everyday language, we often use the term “relatives” generically to indicate anyone who is part of our family. However, for the law and for those who deal with family history, there is a very clear dividing line that defines the nature of our bonds. Understanding this distinction is not just a linguistic curiosity, but allows us to give the right weight to the bonds that regulate our social and legal life, starting from an assumption that often surprises: the fact that the people dearest to us are not, technically, our relatives.
The most emblematic case is that of marriage. Counterintuitive as it may seem, there is no kinship relationship between husband and wife. The bond that unites them is exclusively the conjugal bond. This concept is contained in the very etymology of the word spouse (coniuge), which derives from the Latin coniungĕre and recalls the image of two people placed under the same yoke (iugum). Being spouses therefore means sharing a life path and common responsibilities, but it does not indicate descent from a common ancestor, which is instead the fundamental requirement to be able to speak of kinship in the strict sense.
From the moment two people unite in marriage, however, a new type of bond is born towards their respective families of origin: affinity. As suggested by the Latin origin of the term, ad finis, the affine (in-law) is the one who is “on the border” of kinship. The legal system indeed establishes that affinity is the bond that unites one spouse to the relatives of the other. It is a reflected bond: I become an affine to my wife’s family members because she is bound to them by blood. This bridge created by marriage is fundamental for defining rights and duties, but it has very precise limits.
To understand how “close” a bond of affinity is, one just needs to look at the degree of kinship that unites one’s spouse to their family members. If my father-in-law is a first-degree relative of my wife, he will be a first-degree affine to me. Likewise, siblings-in-law are second-degree affines, exactly as siblings are second-degree relatives to each other. This hierarchy also includes less frequently mentioned figures, such as grand-parents-in-law (prosuoceri), meaning the grandparents of the spouse.
However, there is a point where this network stops extending, and this is where the most frequent doubts often arise. A cardinal rule states that affinity does not generate new affinity. This means, for example, that between the so-called co-parents-in-law (consuoceri) — meaning the parents of one spouse in relation to the parents of the other — there is no legal bond. Similarly, the bond of affinity does not extend to the husbands or wives of our siblings-in-law. Although deep friendships and affection can be created in everyday life, technically these people remain strangers to our official network of affinity. Defining these boundaries helps us to better understand the map of our family and the nature of the bonds that, by choice or by birth, we decide to honor.
