"  Q: As your answer indicates, there is more to OA than green and gold alone; there is also gratis and libre OA. In 2008, you produced a grid demonstrating the four-way relationship among the different types of OA. Can you expand on this, and outline the relative merits of gratis and libre OA? 

A: Gratis OA is simply free of charge. But it’s not more free than that. Gratis literature may stand under all-rights-reserved copyrights and give users no more rights than they already had under fair use (or fair dealing).

Libre OA is free of charge and free of at least some copyright and licensing restrictions. Libre literature stands under some-rights-reserved copyrights, at most, and permits uses that exceed fair use. The advantage of libre OA is that researchers needn’t slow down to ask permission for legitimate scholarly uses that exceed fair use, needn’t take the risk of proceeding without permission, and needn’t err on the side of non-use. By the way, the grid you mentioned was merely a preview of a longer article, which explained the gratis/libre distinction in much more detail."