Then, while I'm not convinced it is anywhere near as separable as you believe, at the very least the book metaphor completely fails to capture the ability to distribute modifications as a first-class entity existing on its own, in this case, block lists and other HTML modification instructions, that can result in millions of people getting the "same" modification in their hands.

I called this the "patch hole" in the law over 20 years ago, in analogy to the Unix patch tool, and I still don't think I've seen a legal system cleanly grapple with what it means to be able to distribute modifications on their own. It is a qualitatively different process and result than having to distribute modified versions directly. It rather directly faces a deontology vs. consequentialism question... if two different processes (distributing changed contents directly vs. distributing patches to an end user and providing combination software) produce the exact same end results, on what basis will the law decide that one is OK and the other is not, since allowing people to distribute change lists provides an effective 100% workaround to the existing illegality of distributing changed works?

I'm not trying to offer an answer here, I'm merely trying to establish that talking about "books" isn't going to give a good grasp on this situation. The metaphor simply doesn't work. It's far too simple to capture too many relevant issues.

How about I distribute a set of pictures with instructions on where to paste them in The Hobbit? That's like a patch or an ad-blocker. Seems fine to me.

> It rather directly faces a deontology vs. consequentialism question... if two different processes (distributing changed contents directly vs. distributing patches to an end user and providing combination software) produce the exact same end results, on what basis will the law decide that one is OK and the other is not, since allowing people to distribute change lists provides an effective 100% workaround to the existing illegality of distributing changed works?

You're going about the question backwards.

If we were basing things on reasonable consequentialism, then downloading a modified version of something you already legally possess would not be a copyright violation.

A patch applied to a singular work for the purposes of modifying it, I think the law could easily decide that the patch itself is a derivative work of the original. A derivative work does not have to contain anything of the original -- it just has to be made from it in some way.

However, something that it's own generic work or not copyrightable (like a block list) would then not be considered a derivative work.

The difference is that a "patch" implies that it is added to exterior content which means that the question of copyright infringement passes to how that exterior content was obtained.

Patching pirated work is still piracy, but patching work you have purchased legitimately (or were given by the copyright holder, such as a web page) is not piracy.

Has your argument been tested anywhere? I'm quite sure that for example in my country it would utterly fail -- the origin of the work is irrelevant in our copyright act.

> I'm merely trying to establish that talking about "books" isn't going to give a good grasp on this situation.

That's a fair point but copyright law was designed with "books" in mind so everything is ultimately related to that. Computers have really put a wrench in what was otherwise a pretty simple system.

This isn't quite right. The law doesn't stop you from selling a book where you have written in the margins, you just can't make and distrubute additional copies of the the new combined work. Though perhaps you could buy books to annotate in bulk and then distribute those legitimat but annotated copies. Actually, that is a decent metaphor for what an ad blocker is doing.