The Stack exchange terms of service have been recently changed since a sentence in them was perceived as too strict by many users.

The change was in this paragraph:

In the event that You post or otherwise use Subscriber Content outside of the Network or Services, with the exception of content entirely created by You, You agree that You will follow the attribution rules of the Creative Commons Attribution Share Alike license as follows:

a. You will ensure that any such use of Subscriber Content visually displays or otherwise indicates the source of the Subscriber Content as coming from the Stack Exchange Network. This requirement is satisfied with a discreet text blurb, or some other unobtrusive but clear visual indication.

b. You will ensure that any such Internet use of Subscriber Content includes a hyperlink directly to the original question on the source site on the Network (e.g., https://stackoverflow.com/questions/12345)

c. You will ensure that any such use of Subscriber Content visually display or otherwise clearly indicate the author names for every question and answer so used.

d. You will ensure that any such Internet use of Subscriber Content Hyperlink each author name directly back to his or her user profile page on the source site on the Network (e.g., https://stackoverflow.com/users/12345/username), directly to the Stack Exchange domain, in standard HTML (i.e. not through a Tinyurl or other such indirect hyperlink, form of obfuscation or redirection), without any “nofollow” command or any other such means of avoiding detection by search engines, and visible even with JavaScript disabled.

The part in bold (emphasis mine) is new. Before, we had the following situation:

  1. A writes an excellent answer on Mathoverflow, and wants to include the same words in his lecture notes or in a book.
  2. However, A is bound by the restrictions of the TOS. For instance, he cannot scan an annotated copy of his own lecture notes and put in on his professional web page: this would violate points b. and d. in the quoted text, as a scanned pdf does not contain hyperlinks.
  3. This seems overly restrictive: why can't A, the original author of the answer, do whatever he wants with it, for instance relicense it?

However, the following slightly more complicated situation could arise:

  1. A writes an excellent answer on Mathoverflow.
  2. B, who is a colleague of A and another Mathoverflow user, wants to include the same words in her lecture notes or in a book.
  3. B sends a message to A: "hey, your answer looks great, can I use it in my lecture notes? I'll cite you as the source of course!". A answers "sure!".
  4. Now B, as a MO user, is bound by the TOS. For instance, she cannot scan an annotated copy of her own lecture notes and publish it on her professional webpage, even if A agrees.
  5. This seems overly restrictive: why can't A, the original author of the answer, do whatever he wants with it, for instance relicense it and grant other people additional rights?

I am not a lawyer and I hope I am reading the TOS correctly this time. My proposed fix is changing the text to the following:

In the event that You post or otherwise use Subscriber Content outside of the Network or Services under the terms of the Creative Commons Attribution Share Alike license, You agree that You will abide by the following additional restrictions:

Note indeed that the four points listed there are not part of the CC-BY-SA license, but are additional restrictions imposed by Stackexchange. There's nothing about nofollow in the CC-BY-SA license, for instance, and links are required only "to the extent reasonably practicable" (in CC-BY-SA 4.0; the TOS do not specify a CC-BY-SA version, but link to the older 2.5 version, which does not mention hyperlinks at all instead).

(Incidentally, not specifying which version of the CC-BY-SA is to be followed looks like another weak point of the TOS).

  • 2
    $\begingroup$ I think your starting sentence is misleading. It was not so much changed as some felt it was too strict, but rather since it said something (or could be understood to say something) it was never intended to say in the first place. $\endgroup$
    – user9072
    Nov 27, 2013 at 17:44
  • $\begingroup$ I think that all the following statements are true: (a) the TOS could be understood to say $X$; (b) the SE staff did not mean to write $X$ in the TOS (at least according to what they say); (c) several users complained that $X$ was too strict. In a scenario in which one of (a), (b), (c) were false, I don't think that the TOS would have been changed. $\endgroup$ Nov 27, 2013 at 19:14
  • 2
    $\begingroup$ I agree with quid, your restatement is misleading and problematic. These clauses in TOS are there to make sure there are not rip-off copies of these sites without attribution. As explained a number of times they are not intended to imply any restriction on how you can use your own content. You can do with your content whatever you want to. $\endgroup$
    – Kaveh
    Nov 28, 2013 at 8:39
  • 1
    $\begingroup$ In short: 1. if it is your content you can do with it whatever you like to, with the exception that you have given SE a CCASA license to use them. 2. if it is not your content, then you are granted a license to use them under CCASA plus the rules as explained there. It doesn't restrict your right to use them under any other license that you might have from the content owner. $\endgroup$
    – Kaveh
    Nov 28, 2013 at 8:42
  • $\begingroup$ @Kaveh I agree with what you are saying, but that's not the complete picture. In addition to the license agreement between A (licensor) and B (licensee), the TOS contain an extra clause that seems to say the following: "whenever you use content that has been published on our site, even when obtained from a third party and licensed in another way, you'll add links back to us at all costs, even if it's impractical". This is an additional agreement in effect between B (if he/she is a user of SE) and SE, restricting B's rights; it has nothing to do with the license agreement between A and B. $\endgroup$ Nov 28, 2013 at 9:03
  • 3
    $\begingroup$ You are misreading it. CC licenses are nonexclusive. See this answer: "This is not an exclusive license. As the copyright owner, you may release your content to anyone under any terms you please, ..." $\endgroup$
    – Kaveh
    Nov 28, 2013 at 9:59
  • $\begingroup$ Frederico, additional restrictions imposed by licensors can invalidate CC licenses, and they often do. Your suggested rewording is much worse than the original! $\endgroup$ Nov 29, 2013 at 8:34
  • 2
    $\begingroup$ The requirements a-d are in conformance with the CC BY-SA license. The CC BY-SA requirements are that, if supplied, you must provide the name of the creator and attribution parties, a copyright notice, a license notice, a disclaimer notice, and a link to the material. Items a-d merely clarify the exact form of each item. It is true that these requirements are to be met "to the extent practicable." Indeed, b only applies to Internet uses and the rest are practicable by any medium reasonably capable of handling the content itself. $\endgroup$ Nov 29, 2013 at 8:42
  • 1
    $\begingroup$ I think this question on the CC FAQ can help framing the issue. We're not speaking about violating the CC license here, we are speaking about violating the Stack Exchange TOS, which is a completely different agreement between different parties. I remain convinced of my point, but won't insist further. $\endgroup$ Nov 29, 2013 at 9:48
  • 1
    $\begingroup$ See also this CC FAQ. $\endgroup$ Nov 30, 2013 at 14:20

3 Answers 3


All that assumes that there is some noticeable portion of users who bother to read "Terms of service", which, I'm afraid, is a rather unjustified assumption :-) So, it will, most likely, continue as usual: everybody will stick to his own common sense and customs until StackExchange will try to sue someone, which might be the end of MO and other SE sites as we know them.

  • 14
    $\begingroup$ While this is absolutely correct, I still think it's very valuable to try to get the legal setup to match "reality". We might be in somewhat less trouble with academic publishing if we'd insisted much earlier to have "on paper" the rights (publishing in repositories, use for educational purposes) we planned to enjoy anyway. $\endgroup$ Nov 28, 2013 at 7:54

I'm certainly not a lawyer. Nevertheless, I think you've made a mistake.

If I want to copy some content from MathOverflow, regardless of my conversations with the original author, I better abide by both the Terms of Service, and also the license under which that content was provided.

At the same time, if the author wants to relicense their content to me, under perhaps different terms, they can do that. I can then use their content under that license. (Perhaps I better not say that it's from MathOverflow now, because it isn't.)

You seem to draw an invalid conclusion: that I am compelled to use the content under the terms of the license via MathOverflow, even when an alternative license is available.

  • 6
    $\begingroup$ I'll say further that your setup is getting to be rather hypothetical! Why not just cite the content as coming from MathOverflow (just like you cite someone's paper as being in a particular journal)? Make your best effort to provide hyperlinks, subject to the constraints of the medium, and I think you're good to go. $\endgroup$ Nov 27, 2013 at 11:06
  • 2
    $\begingroup$ I am not sure. Subscriber content is defined as "Content posted by Subscriber". If I take the same content from another source, is it still "subscriber content" or not? If so, then the agreement between B and Stack Exchange binds her to abide by the additional restrictions, independently of A's opinion. $\endgroup$ Nov 27, 2013 at 11:17
  • 1
    $\begingroup$ Re your comment, I agree with you that this is the ideal setup. The problem is that "your best effort to provide hyperlinks" is enough for CC-BY-SA and for common due-reference ethics, but not for Stack Exchange, who added these additional restrictions to the license. $\endgroup$ Nov 27, 2013 at 11:20

In the event that You post or otherwise use Subscriber Content outside of the Network or Services ....

I think that saying, “Hey, B, I’m allowing you to use my notes” counts as using, in the above terminology. So in this case A can do whatever zie wants with zir MathOverflow content, and that includes the right to license it to B under any license.

  • 3
    $\begingroup$ I suppose I should think of Spivak or Sweden when I read this answer, but I can't avoid thinking of Boris Badenov instead. $\endgroup$
    – cardinal
    Nov 27, 2013 at 22:31

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