Yair said:
Can someone designate a term in the public domain as Product Identity? For example, may I claim "Tir Nan Og" (the Celtic "fairyland") as PI?
Sure they can. Doing so has no effect on anyone's ability to use that term however, as it is in the public domain, and can thus be independently sourced by anyone. Making a PI claim over something that a publisher did not independently create is essentially pointless, but legal.
Can one designate an entire section of the work, say a chapter, as PI?
Sure.
Can he do so if it contains derived game mechanics, e.g. a Save DC?
Yes, although this question leads to my conclusion that you don't really understand the point of Product Identity.
The product identity clause in the OGL exists for 2 reasons:
1: To make ABUNDANTLY CLEAR to any 3rd party user what parts of the work the publisher DOES NOT wish to allow others to use per the "open" concepts embodied in the OGL. it serves as a mechanism for communication, so that misunderstanding can be avoided.
2: It allows closed and open content to be editorially mixed without requiring obfuscating formatting. The PI concept is what allows simple, human readable statements like "Darth Vader has 5 hit points", while keeping what needs to be open ("hit points") legally bounded from what needs to be closed "Darth Vader".
The purpose of the Product Identity clause is not to perfect copyright or trademark interest a publisher might have in a work. The legal system already does that; it's not the OGL's water to carry.
Can he designate the entire work as PI excepting the designated OGC?
Sure.
If so, what's the effect on the derivative work?
You could use the OGC, but not the PI.
If I designate an entire chapter as PI, does it mean that no one downstream can copy the entire chapter verbatim (just like someone can say "Tir Nan Aken" without violating the "Tir Nan Og" PI), or that no one can say "The" (as that word is part of the text in the PI chapter)?
It means that to the extent that the material you designated as Product Identity exists in no form other than that you created yourself (or that you have licensed from some 3rd party who did create it), nobody else can use it without your permission. Since you are not the person who created the word "the", your Product Identity claim has no real-world effect.
Now, lets talk about Conan.
Conan is just a word. Nobody can "own" that word. It existed so long ago that any copyright or trademark claim on it would have long expired. The use of "Conan" as a name cannot be owned. The are hundreds of thousands of "Conans" in the world, in fact, there are probably more fictional characters named "Conan" than there are living human beings. If you claimed "Conan" as Product Identity, your claim would be valid, legal, and pointless. There is no way you can demonstrate that
YOUR use of the word "Conan" or the name "Conan" eliminates
MY ability to use that name in my works, even if they use OGC provided to me from a source which claims "Conan" as Product Identity. If you sue me, I'll have the unanswerable defense: "I'm not referencing your "Conan", I'm referencing some historical person, or public domain character of that name.
Now, if you had the proper licenses, and if the copyright and or trademark is still valid, it is possible that you
might be able to assert a useful Product Identity claim on the term "Conan The Cimmerian". A 3rd party who wanted to negate your PI claim might have a very hard time finding any examples of a public domain Conan who was Cimmerian.
Now let's take this one step further. Instead of a text usage, let's envision a painting.
If the painting is of the Conan character, as portrayed by Ah-nold in the "Conan the Barbarian" movie (or sequels) and you claimed
THAT as PI, you'd have a very strong case if anyone attempted to circumvent your claim. The combination of image, name, and character create a "nexus" which is easily separated from the public domain background of generic "Conan".
Imagine that I create a work of fiction, in which I have a character named CONAN. That would be the
COmputing
Network
Administratio
N system who is the hero in my cyperpunk thriller about the brain-scan image of a serial killer loose in cyberspace who is murdering AIs. if I define my Product Identity as "the character CONAN as depicted in this work", I can probably assert a PI claim against you if you use my OGC in a derivative work featuring a digital gumshoe named CONAN.
Product Identity can best be described as a "No Trespassing" sign around content that can be legally protected using other means, not as a kind of IP force field that converts public domain content into closed content by merely wishing it to be so.
Ryan