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The Sosa-Stradonitz or Ahnen Numbering System is designed to number yourself as 1, your parents as 2 and 3, grandparents as 4 through 7, great-grandparents as 8 through 15 etc.

In my case, my father's father died when my father was only 6 months old. When my father was 5, his mother remarried. My father's step-father raised him as a father. I feel it is my obligation and my desire to trace both of my father's fathers.

My father's first father is technically number 4, and his parents are 8 and 9, and grandparents, 16 through 19.

How can I number my father's step-father and his ancestors so that I can designate his line equivalently and with equal importance as my other lines?

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The ahnen numbering system is a straightforward method of numbering ancestors. More precisely, it actually does not number ancestors, but ancestral slots, whether any ancestors are known or not, and it assigns just one number to each slot. When pedigree collapse occurs, a single ancestors appears in multiple slots, and thus has multiple ahnen numbers. When there is both a biological and an adoptive father in the same slot, there still is just one number for that slot. Simply assigning the same number to both fathers is a no-no; different individuals must have different numbers.

Two fathers can be assigned the same report number, just not at the same time, in the same report. You can show the biological father in one report, and the adoptive father in another. That way, they'd receive the same report number in two different reports.

You desire is to show both fathers in the same ahnenlist, and still use ahnen numbering. Adopted children are easily accommodated in descendancy reports, but there seem to be few attempts to accommodate multiple pairs of parents in ancestral overviews. The only one I know of is one I created and called the Extended Ahnenlist, introduced in Adapted Ahnenlist. Alas, using an Extended Ahnenlist is easier said than done, because no genealogy software provides this report type it yet.

The Adapted Ahnenlist article was published in 2010, just before the articles that introduced scientific genealogy, and that shows. The terminology used needs work, but I'll use the same terminology here for consistency's sake.

The article illustrates the Extended Ahnenlist with a tiny example involving both biological and adoptive parents, distinguishing between a birth ahnenlist that shows only biological parents, and a family ahnenlist that shows all the families that did the parenting. A family ahnenlist includes both sets parents, and they do receive the same ahnen numbers, but not the same report numbers.

The extended ahnen numbering scheme used involves more than just the ahnen number; the number is suffixed with either A or B; A for Adopted, and B for Birth / Biological. The article expands on this basic idea by briefly discussing dealing with earlier generations, multiple adoptions in the same ancestry, and multiple adoptive parents for the same child.

You are in the fairly unique position that you develop your own genealogy software, and I believe you will not find it hard to implement this report type.

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  • Yes, this can be implemented. But I wonder ... should it be? Or are fixed numbering schemes ready to be replaced by a dynamically changable focus point, where numbering just gets in the way. Thank you Tamura, for the insight and for something to think about.
    – lkessler
    Oct 23 '12 at 4:37
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    Other thoughts: A=adoptive, B=biological. We can add others as well, e.g. F=Foster, S=Surrogate. There could be multiple adoptive fathers or mothers, so A1, A2 etc.
    – lkessler
    Oct 23 '12 at 4:41
  • An interactive and graphical display offers many possibilities, but numbering schemes remain useful for printed text. Oct 23 '12 at 4:47
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Under the "rules" of the Sosa-Stradonitz system, individuals in your father's second father's line have no standing as your direct ancestors and so cannot be assigned a number. The issue is the same as asking "How can I assign a number to my favourite great-uncle?"

The difficulty you face is one of the consequences of our move from a strict genealogical view of descent to the more inclusive world of family history. Tools created for one set of needs do not always adapt to another.

The work-around would be to create a second tree for your additional family line. The cleanest system would be to make your step-grandfather the focal person, but if you want to automatically assign numbers for Ahnentafel then add yourself and your father at 1 and 2 then build from there. If you include your mother (3) and paternal grandmother (5) you run all the risks usually linked with tree duplication.

The purists will be appalled but you could then refer to an ancestor of your father's stepfather in a narrative as, for example, 33S (who would, in effect, stand in the place of the person given the "real" 33 by the standard rules.)


If you accept that Ahnentafel cannot do want you want and that attempts to hack it are unacceptable, then you need to explore other numbering systems (of which there are many).

For a non-specialist overview go to Wikipedia: Genealogical numbering systems. When considering these, be aware that most were developed to overcome a perceived shortcoming in one or more of the others. But there is not one that does everything.

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    This is an example of the technology (the numbering system) driving the research and falling short in the process. If you have to resort to using a work around it is an inadequate tool.
    – Sue Adams
    Oct 20 '12 at 8:05
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    @SueAdams The "technology" is more than 500 years old. In that time, quite a few people have tried to extend its functions. For its stated purposes it is an excellent tool. If we want to perform some other task with it, some hacking is necessary. Whether that is an acceptable, is a matter of personal preference.
    – Fortiter
    Oct 20 '12 at 10:08
  • What do you mean by "33S"?
    – lkessler
    Oct 21 '12 at 5:52
  • By 33S I intend to signify "the other 33", that is, not the person (the great grandmother of his father's biological father) designated as 33 in a standard Ahnentafel. Take your pick of whether the letter s comes from second tree or shadow tree or step tree.
    – Fortiter
    Oct 21 '12 at 6:32
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The only correct answer is- you can't; at least not without lying to the software.

An ahnentafel deals with bloodline ancestors and your step-grandfather doesn't qualify.

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  • If ahnentafel numbering can't be extended, then what should I use instead?
    – lkessler
    Oct 21 '12 at 5:53

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