Because I want others to freely sample my work, and be able to copyright their own "derivative" works incorporating my work, and yet still have my work legally protected against plagiarism.
Normal copyright status, assigned automatically to any work the moment it is created, prohibits reproduction and/or use of a work without the express permission of the original author. In the interest of sharing these educational resources with as wide an audience as possible, I chose to "license" them with a short legal document explaining my intentional surrender of certain rights normally secured by copyright. This process is whimsically referred to as copyleft. So, the problem files and computer scripts comprising these Socratic worksheets are copyrighted under my name, but anyone has permission to make copies for themselves, use them, distribute them, and even sell them. The only legal restriction is that no one may claim my original work as their own creation.
Many similar, "free" projects utilize strongly worded "copyleft" licenses that not only protect the original authors' work while permitting fairly unrestricted redistribution and modification, but also extend those protections and freedoms to anyone else who might modify the work to create their own "derivative" work. Perhaps the best-known example of a copylefted work is the Linux computer operating system, most of the constituent software pieces being licensed under the GNU General Public License, or "GPL". This license maintains that not only are the original works free to copy, distribute, and modify, but all "derivative" works (the result of someone other than the original author making modifications) must remain free as well. This is true even if the derivative work required substantial investment of time or money to create. However, for this project I have chosen to use a "weaker" license for the purpose of permitting recipients of my materials to restrict access to their derivative creations if they so choose.
My reason for doing this is as follows. First, I want the information here to be widely distributed and used by teachers everywhere. Even if not in the context of teaching electronics, the principle of modular, Socratic worksheets for inquiry-based teaching holds great promise for instructors and students everywhere. Copyleft licenses such as the GPL, which enforce the condition that derivative works must retain the same freedom as the originals, sometimes discourage others from investing effort or money into making derivative works because whatever improvements and additions they may make to the material will be "tainted" (some would say "infected") with the same binding condition.
If the sole issue is money -- i.e., copyleft prevents a corporation from obtaining a copy of Linux, adding their own modifications, and then copyrighting the derivative operating system so as to secure exclusive sales rights to it -- then copyleft makes ethical sense. After all, most would consider it greedy to profit from a gift, especially if that profit is secured by exclusive, legal right. And if strongly-worded copyleft licenses prevent this kind of exploitation, aren't they a good thing? In the world of education, though, there are ethically sound reasons for not wanting material to be free and open to the public. Test answers, for example, must be kept secret from students for obvious reasons. Instructor lecture notes are often not intended for student viewing, either. In the case of these Socratic worksheets, if a teacher copies them and adds their own detailed references in a separate section for each question file (for the benefit of anyone teaching the course at that school), it would be prudent to keep the added information secure from students, so they cannot "cheat" by viewing that teachers' research rather than doing their own.
I was faced with this very dilemma when making these worksheets: do I add a section to each question file containing my own detailed answers and research for each question, for the benefit of instructors who would teach with these materials, knowing that students could go to the same website and download all this pre-compiled work? My solution was to not place anything on the website that students shouldn't see, and let instructors develop their own additions to the problem sets. But then the same legal problem remains: if these works are protected under a strong copyleft license, any additions made by other instructors would legally have to remain open to the public as well. Contentious students could legally demand access to the instructor's additions. This potentially compromises academic integrity.
Releasing my works into the Public Domain might avoid such problems (although there are some who argue there is no such thing as a Public Domain, given the aggressive nature of modern copyright law in America). However, I do still want to retain the right to attributive credit: it is important for my own interests that whatever material I create is at least credited to me. If I were to relinquish all rights and release works into the Public Domain (assuming I even can!), it might be possible for someone to claim my works as their own original creation. Plagiarism is not my biggest concern. Rather, it is that someone might try to prevent me from posting this material on the internet by claiming it is their material and that I am violating their copyright. In a world full of opportunistic, litigious people, one is forced to consider such possibilities.
So, my final solution was to employ a more permissive form of "copyleft" to these works, the only legal right I retain being the right of attributive credit for my creation. The Creative Commons "Attribution" License fit this need perfectly. Under this license, anyone is legally permitted to download the files, make copies, distribute them to others, modify them as desired, and even place their own (restrictive) copyright on their "derivative" creations. This way, my personal choice of releasing information freely does not become a binding condition for anyone else.