[License-discuss] Becoming Public Domain After X Years

[Martin L]

Hi all,

I was wondering if anyone had links/knowledge about licenses which,
after X amount of time (say, 10 years), release the code into the public
domain?

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To clarify why I'd want this, there are two reasons. The first reason is
that, as someone who'd like copyright lengths to be reduced, it only
makes sense to make my own work enter the public domain more quickly.

The second reason is that I like strong copyleft, but I don't trust any
current license to stand the test of time. However, all the ways I know
of relicensing works are flawed in some way. Contributor license
agreements give too much power to one person/organization. Asking every
contributor to relicense their code is a good option, but as projects
get big and old doing this can become nigh-impossible.

By having all the code enter the public domain after 10 years,
relicensing the project would still require broad community agreement,
since it would require every new contributor to use the new license, and
then waiting 10 years, but it would always be feasible. If you can also
get all the contributors from the past X years to relicense, you only
have to wait 10-X years.

I don't expect this to significantly weaken the copyleft, since 10
years' worth of patches is a pretty strong incentive to use the most
recent (and still copylefted) version. And while 10 years might seem
long, it's not /that/ long, and this waiting period is in many ways a
feature, since relicensing shouldn't be easy. 10 years might even be too
/short/. If that turns out to be the case, it might make sense to go for
15 or 20 years.
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The idea I had to implement this would be a dual-license, the main
license being copyleft, and the second license being CC0, with a line
saying you can only use it under the terms of the CC0 starting from a
specific date.

This is the text I wrote for it, that would go into a COPYRIGHT file in
the project:

> This project is licensed under the terms of <insert copyleft license here>.
> Starting on midnight UTC of January 1st 2030 <2030-01-01T00:00Z>, this
> project may instead be licensed under the terms of the CC0 1.0 license,
> at your option.

And then each year you would increment the year in the COPYRIGHT file.
In this way every snapshot of the project made in a given year would
enter the public domain around 10 years after being committed, on an
unambiguous date.

I have no idea if this would work legally, it's basically a "crayon"
license. But my (relatively weak) search skills are failing me, and I
can't seem to find anyone who's done something like this before, so this
is all I've got.

Anyway, thanks for reading, and thanks in advance for comments/links!