The original thread can be found here: Stack Exchange and Stack Overflow are moving to CC BY-SA 4.0

As far as I understand, Stack Exchange can move on to CC BY-SA 4.0 for content published in the future, but they are not allowed to unilaterally change the license of previous publications. Several threads have been created requesting answers regarding this issue from Stack Exchange, however, the only answer from moderator did not give any meaningful explanation.

Since this is a legal issue, I would like to ask of Law Stack Exchange community to give expert opinion on this matter.

Can Stack Exchange change the license for previously published content without the consent of users?


2 Answers 2


What SE can do is controlled primarily by the Terms of Service. What most matters is the section on Subscriber Content, which says:

You agree that any and all content, including without limitation any and all text, graphics, logos, tools, photographs, images, illustrations, software or source code, audio and video, animations, and product feedback (collectively, “Content”) that you provide to the public Network (collectively, “Subscriber Content”), is perpetually and irrevocably licensed to Stack Overflow on a worldwide, royalty-free, non-exclusive basis pursuant to Creative Commons licensing terms (CC-BY-SA), and you grant Stack Overflow the perpetual and irrevocable right and license to access, use, process, copy, distribute, export, display and to commercially exploit such Subscriber Content, even if such Subscriber Content has been contributed and subsequently removed by you...

This means that you cannot revoke permission for Stack Overflow to publish, distribute, store and use such content and to allow others to have derivative rights to publish, distribute, store and use such content. The CC-BY-SA Creative Commons license terms are explained in further detail by Creative Commons, but you should be aware that all Public Content you contribute is available for public copy and redistribution, and all such Public Content must have appropriate attribution.

This part has not changed: the purported license is still "CC-BY-SA", and the TOS does not explicitly specify a version. What apparently has changed in the relevant section is one "helpful information" link, which now points to https://creativecommons.org/licenses/by-sa/4.0/. So the interesting question arises whether that would constitute an unpermitted post-hoc change in the terms by which SE has license to my older stuff. This matter came up in a reviled Meta question; as I pointed out, the TOS also included a merger clause that

This Agreement (including the Privacy Policy), as modified from time to time, constitutes the entire agreement between You, the Network and Stack Exchange with respect to the subject matter hereof. This Agreement replaces all prior or contemporaneous understandings or agreements, written or oral, regarding the subject matter hereof.

Because of that, the TOS is self-contained and stuff found on other web pages are not part of the agreement. This in itself is a bit of a problem because you can't both say "we're not bound by stuff outside of this page" and say "the specific terms of the license are outside this page".

That particular clause is gone, but there is an analog in the current TOS:

These Public Network Terms represent the entire agreement between you and Stack Overflow and supersede all prior or contemporaneous oral or written communications, proposals, and representations with respect to the public Network or Services or Products contemplated hereunder.

Furthermore, the TOS contains the following "we can change it" clause:

Stack Overflow reserves the right, in its sole discretion, to modify or replace these Public Network Terms, as our business evolves over time and to better provide Services and Products to the Stack Overflow community, or to change, suspend, or discontinue the public Network and/or any Services or Products at any time by posting a notice on the public Network or by sending you notice via e-mail or by another appropriate means of electronic communication.

I assume but do not know for a fact that a similar clause existed in prior versions of the TOS. So I conclude that the change is legal.

  • 2
    Correct me if I'm wrong, but this seems like it addresses if one can change the license used for new contributions rather than change the license granted for old contributions. Let's take you and me as an example. If I write an article and grant you a CC-BY-SA 3.0 license to it, can you then distribute it to others under CC-BY-SA 4.0? I don't think anyone is questioning that the TOS can be updated whenever and continued use of the service is acceptance of the TOS. Oct 1, 2019 at 18:10
  • I can't because you specified a particular version, also because you didn't grant me any power to change the license terms.
    – user6726
    Oct 1, 2019 at 19:00
  • 4
    In the case of Stack Exchange, does anything in the TOS grant the power to change license terms? Does the fact they don't call out a version matter, one way or the other, since one version is linked to explicitly? Oct 1, 2019 at 19:03


The relationship between Stack Exchange (SE) and it’s users is governed by the ToS - a contract subject to all the normal contract law applicable in due to the choice of law clause it contains. Common law (unlike civil law) treats licences no differently from any other contract (See What is a contract and what is required for them to be valid?). Note that this is only the latest version, versions back to 2010 can be found here.

Changing a contract requires one of two things:

  1. Agreement of all parties with all of the requirements of a new contract.
  2. A provision in the contract allowing the change, commonly referred to and sometimes specifically identified as a variation clause.

The discussion on the linked question is focusing on 1. - SE’s legal authority comes from 2.

Specifically, the Creative Commons licence is only part of the contract between SE and it’s users: it cannot be read in isolation. There is nothing unlawful about incorporating documents into a contract by reference: indeed if you think of complex contracts like those in building and construction there is no practical way not to do it.

The ToS give SE the right to change the ToS unilaterally - in the current ToS its in clause 10.d and in the 2010 ToS it’s in Clause 13.

This allows them to change anything including the copyright licence.

There is no conflict with the CC licences, from the upgrade guidelines:

Existing content:

  • If the contributors, then need permission to relicense. Without permission (via terms of use or otherwise), then that content remains under prior version.

Everyone who has ever posted agreed that the licence (and everything else) could be changed when the ticked “I agree to the ToS” when they created their account.


There is nothing wrong with allowing unilateral changes to the contract, however, in the US the exercise of a contractural power must be done in good faith, that is, with due consideration for the negative impact on the other party.

  • 4
    This is an interesting interpretation, but is there any precedent? I agree that 13 and now 10(d) give SE the right to change the ToS at any time for continued/future use of the service, but I'm still not clear on how changing the ToS can change licenses retroactively. As you said yourself, it's a combination. Also, how does this affect people who have not agreed to the change in ToS (such as by not using the service at all since the change was made)? Oct 2, 2019 at 8:20
  • 1
    This seems like a reasonable answer now. I've been involved in contracts and licensing (particular open source software) for about 5 years now. I'm not a lawyer, but I interact with lawyers on this subject several times a year. It's not obvious to me, so it must be even less obvious to people with even less experience and exposure to this subject that the license granted can be changed retroactively. It seems like this would even allow for changing to a totally different license instead of just a newer version of the license, which could be problematic considering the non-obviousness of this. Oct 2, 2019 at 8:42
  • 2
    You seem to be arguing that SE can retroactively give itself new rights to existing content, even if (previous) Subscribers do not agree to the change (non-agreement can typically be indicated by closing the account). Let's say SE changes this from a non-exclusive license to an exclusive license, which would deprive (previous) Subscribers from the right to use their own content. Do you think such a change would be possible? Or do you think there are limits on how the license can be changed?
    – amon
    Oct 2, 2019 at 17:04
  • 1
    @DaleM I'm not familiar with New York law, but to my European ears a perpetual contract where one party can't object to the other's unilateral changes sounds unconscionable. I'll also point out that 10.c lists sections that survive termination of the contract, which does not include the modification clause 10.d. Termination of the contract is not further defined, though 5.2 mentions the right to terminate the account.
    – amon
    Oct 2, 2019 at 21:32
  • 1
    @amon unconscionably is in the execution - not the drafting. Contracts are full of terms that are unconscionable in certain circumstances but if they never come up the contract is not unconscionable.
    – Dale M
    Oct 2, 2019 at 21:41

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