The purpose of a Share Alike license is to ensure that all future adaptations and derivatives of a work carry the same permissions as the original. This way, no matter what new forms the work takes on, it will always be free, open and licensed for re-use.

Here’s the description of Share Alike in the human readable Commons Deed:

Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license.

Here’s the pertinent language in the legal code:

You may Distribute or Publicly Perform an Adaptation only under the terms of: (i) this License; (ii) a later version of this License with the same License Elements as this License; (iii) a Creative Commons jurisdiction license (either this or a later license version) that contains the same License Elements as this License (e.g., Attribution-ShareAlike 3.0 US)); (iv) a Creative Commons Compatible License.

In other words, if you make a derivative work based on the Share Alike-licensed work, you must release it under the same terms under which the original was released, either using the appropriate CC license or an approved compatible license. As of this writing, CC has not approved any licenses for compatibility, so for all intents and purposes, the Share Alike license requires you to license derivative works under a CC license. If you cannot apply the appropriate license to your derivative work, or do not wish to, then you usually shouldn’t adapt Share Alike-licensed works.

The important thing to remember about Share Alike licenses is that, with one exception [see below], the Share Alike provision only applies to derivative works, which the license calls “adaptations”. Verbatim or unaltered copies are not derivative works. They’re simply copies, and as long you comply with the other terms of the license you can make exact copies of an SA-licensed work without applying a license to the work in which it’s used.

What is a derivative work?

It’s a bit complicated.

According to Title 17 Section 101 of the Copyright Act:

A “derivative work” is a work based upon one or more preexisting works, such as a translation, musical arrangement, dramatization, fictionalization, motion picture version, sound recording, art reproduction, abridgment, condensation, or any other form in which a work may be recast, transformed, or adapted. A work consisting of editorial revisions, annotations, elaborations, or other modifications which, as a whole, represent an original work of authorship, is a “derivative work”.

The key words here are “recast, transformed, or adapted.” A derivative work involves enough creativity and originality that it constitutes a new copyrightable work. Simply converting a work from one medium to another — from print to digital, or CD to MP3 — does not produce a derivative work.

One Big Exception

There is an exception to the “Share Alike only applies to derivative works” rule: Songs used in video. Share Alike licenses use the word “adaptation” instead of the legal term “derivative work,” and include this language in the definition of “Adaptation”:

For the avoidance of doubt, where the Work is a musical work, performance or phonogram, the synchronization of the Work in timed-relation with a moving image (“synching”) will be considered an Adaptation for the purpose of this License.

Using an unaltered song in the soundtrack to a video does not make the video a derivative work, because the song itself has not been recast, transformed, or adapted in any way. However, the language above extends the definition of adaptation to include “synchronization of [music] with a moving image,” which means that as far as Share Alike licenses are concerned, videos that use an SA-licensed song are adaptations and must be released under the same SA license as the song.

The summary: In general, the Share Alike requirement of SA licenses only applies to derivative works, except when that work involves combining SA-licensed music with film or video, in which case, the film or video must carry the appropriate SA license.

Examples

Examples of adaptations as defined by the SA license

• Translating a short story from one language to another
• Photoshopping a picture to add to or alter its original elements
• Using a sample from one song to make new song

Examples of things that are not adaptations as defined by the SA license

• Including a short story in a collection of short stories
• Reproducing an unedited image on a website
• Using an unedited video in the background of a live concert

Two things to keep in mind

1. Creative Commons licenses do not affect your fair use rights. If you have a use in mind that is also probably a fair use, the application of a Share Alike license does not require you to release the resulting work under an SA license.
2. If you would like to use a CC-licensed work in a way that is not permitted by the license, you can ask for permission. Copyright holders are free to offer as many different non-exclusive licenses as they wish. Share Alike licenses don’t rule out the possibility of making an adaptation that doesn’t carry a Share Alike license, you just have to ask for permission to do so.

Previous CC-HOWTO’s:
How to attribute a Creative Commons licensed work
How to use a work with a NonCommercial license