You must either own an ID card or a passport. This means having an ID card is optional. Does the German passport have a unique identifier as well? (never owned one) The tax number otoh is assigned at birth.

Yes it has a unique ID

Which changes whenever you get a new passport. Not what we would call a primary key in database design.

And a person can have more than one German passport

With a strong motivation yes, just for fun no.

One motivation is that you want to travel to Israel and to some Arab country, which do not accept passports with stamps of the "enemy" in it.

I don't know if they verify the motivation in any way or whether it's enough to say so.

There are (according to the BMI[1] (German interior ministry)) only two reason to have multiple passports: The first being the one you stated and the second being multiple (visa requiring) travels in a short enough timeframe so that your passports would have to be lying at the foreign countries embassies/consulates at the same time.

Seems like motivation enforcement is quite strict, as they do state that you can't even get two passports for the "enemy visa" reason when the visits are just planned, but you can't prove it yet (palne tickets etc.) you won't get it, and you'll have to go to the German embassy after you can prove it...

[1]https://www.bmi.bund.de/SharedDocs/faqs/DE/themen/moderne-ve...

One of the two tax number systems is, yes :)

There’s also another one which changes every time you move across financial administrative districts.

No, that is a document ID and changes with each reissuance.

Germany has had a constitutional restriction in place explicitly prohibiting an SSN equivalent.

These days, the tax ID can supposedly be used for that purpose, but I haven’t seen much use of that yet.

> Germany has had a constitutional restriction in place explicitly prohibiting an SSN equivalent.

Very interesting! Thank you for this

Unfortunately it's not a clearly written clause. It's derived from the dignity of humans and similar general terms. So the interpretation has changed over the decades. As long as the GDR existed it was clearly considered a property of a totalitarian state. Existed in the GDR (East) but unthinkable in the Federal Republic (West). Maybe 15 years after reunification (don't quote me on the exact number) a permament nationwide tax id was introduced. With the promise that its usage will forever be limited to tax offices and exchange with any other authorities is illegal. Another 15 years later that promise was "forgotten" and now the tax id can be exchanged with many authorities. It's relatively new and probably not widely used yet. But the dams have been opened.

That sounds a bit like how SSN use in the US has broadened from its original scope. Any government power, once granted, seems only to ever increase in scope.

Yes, that's a better explanation of the constitutional status, thank you! (Supreme court decision vs. an explicit clause in the constitution.)

FWIW, I think in this age of massive databases that can be effortlessly joined on fuzzy matching criteria, the lack of a unique person identifier is more of a hurdle for legitimate use cases than a safety measure against government or corporate overreach.

One good thing about it is the complete lack of the horrible "SSN as both primary key and bearer authentication token" pattern that's commonplace in the US, though – but the alternatives are pretty annoying, in my experience.

> No, that is a document ID and changes with each reissuance.

TIL. My last and current number had the first 4 characters the same, so I didn’t even realize that (and the times before I never thought of it).