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Background:
While I know that copyrights on open source products expire. I have never come across anything regarding licenses, this lead me to ask this question:
My Question:
Can licenses expire?
If yes, under what conditions? Is there a time limit? If no, why do copyrights expire but not licenses?
Licenses exist to specify rights that the copyright-holder gives to license-holders; they only have meaning within the context of copyright legislation. So when copyright expires, the limitations linked to copyright expire as well, and the need for a license disappears. You could view this as meaning that a license expires when all the copyrights on the work it licenses expire themselves.
Once a work is in the public domain you don't need a license; you can do anything you like with it.
It is possible to specify termination clauses in licenses, but that's not quite the same as expiration. You could write a license with an end date (but that wouldn't qualify as a free / open source license, unless upon termination it reverted to another free / open source license). The GPL v3 includes a termination clause (section 8), but it only terminates the license for people who violate the license terms (so it's not expiration).
In general, a license can be for a limited time.
All open source licenses are perpetual licenses. Neither the FSF nor the OSI consider non-perpetual licenses for certification.
When the copyright expires, the license is redundant, as it can't enforce any conditions anymore.
