Sooner or later, during your genealogical research in Portugal, you'll encounter the expression consanguinity in the nth degree, with no explanation of what that degree really means.
To answer that question, we need to distinguish between two legal systems:
- Canon Law
- The consanguinity degrees usually found in genealogy are mentioned in the parish records for baptisms or marriages, which use the Canon Law of the Catholic Church. According to this law (which went into effect in 1215), any marriage is forbidden between two persons with up to four degrees of consanguinity, being necessary to request a waiver from the Church authorities to marry. To calculate the canonic degree between two individuals, you simply count the number of individuals until the common ancestor (see in the figure the number at bottom left). Using this method, the marriage with a second cousin would have the 3rd degree of consanguinity, the same as with a great uncle, since the common ancestor is the same (the great grandparent). In 1983, a new Canon Law was approved, that started to use the same calculation method as the Civil Law, keeping the marriage impediment up to the 4th degree of consanguinity.
- Civil Law
- The Portuguese Civil Law approved in November 25th, 1966, even though it has been repeatedly modified, preserves the same method to calculate the degrees of kinship in its Article 1581:
- Na linha recta há tantos graus quantas as pessoas que formam a linha de parentesco, excluindo o progenitor. [In the straight line, there are as many degrees as there are individuals who form the kinship line, excluding the ancestor.]
- Na linha colateral os graus contam-se pela mesma forma, subindo por um dos ramos e descendo pelo outro, mas sem contar o progenitor comum. [In the collateral line the degrees are calculated the same way, climbing one of the branches and descending the other, without counting the common ancestor.]
This degree differs from the canon degree prior to 1983, and in practice it is simply the number of individual in the two kinship branches minus one (see in the figure the number at bottom right).
In the figure, it is presented also the common term for the degrees of relationship, being that the Portuguese language is missing an authoritative definition of the correct terms for the chidren of the great-n-uncles (purple section) and the children of the cousins (blue section). The needed terminology should fulfil the following goals: to be a coherent system and in line with the common use of the language; to identify the relationships objectively; and finally not give rise to confusion between the different types of kinship degrees involved (e.g. second cousin and never cousin in the second degree).