Sosa-Stradonitz ascending numbering

It is essential to give your ancestors a number so that you can find your way around.

There are several numbering systems, depending on whether you are working in ascending or descending genealogy.

In ascending genealogy, you generally start with yourself.

In descending genealogy, you start with an ancestor, in order to find all his descendants.

This system was invented by the German Michel Eyzinger in 1590, followed by Jérôme de Sosa in 1676 and Kerule von Stradonitz in the 19th century.

His numbering system is the most practical and widely used for establishing an ascending genealogy.

Principles of sosa numbering

• Each ancestor has an invariable number.
• The numbering starts with the person whose ancestry is being traced, the de-cujus (glossary), who bears the number 1.
• His father is number 2 and his mother number 3.
• Number 4 is his paternal grandfather, number 5 his paternal grandmother, number 6 his maternal grandfather and number 7 his maternal grandmother.
• And so on…

Rules for sosa numbering

• An even number always refers to a man, an odd number to a woman, except of course for number 1, which is either a man or a woman.
• A father's number is double that of his child.
• A wife's number is her husband's number plus 1.
• A mother's number is double that of her child plus one.

Notes on sosa numbering

• The first number of a generation gives the number of ancestors in that generation. For example, the number 16 indicates that there are 16 ancestors in the 5th generation.
• The same ancestor may appear several times in the genealogy: this is called an implex (glossary). In this case, the ancestor has several sosa numbers.
• The sosa number established is only valid for an individual. For children or grandchildren, the numbering has to be redone.
• This system only takes direct ascendants into account. Collateral relatives do not have a number.