There’s a phrase I love explaining to people, because I’ve only met about two or three people who understand it: “the exception that proves the rule”. Most folks think it means “the thing that does not fit a rule proves that a rule is in effect.” For example, if you assume all fighters have low Intelligence, a fighter with high Intelligence is the exception that proves the rule. This fighter does not fit the rule, so it means that all other fighters do fit the rule. If this sound ridiculous, that’s because it is. It’s the sort of understanding you get if you don’t think about the things you say or hear.
What it actually means is “an exception to an unstated rule is proof that a rule is in effect beyond the exception.” That is, a sign with “parking allowed here on Sunday” implies “parking not allowed here on days other than Sunday.” The exception is “parking on Sunday”, and the rule is “no parking any time”. The sign does not need to say “parking is normally not allowed here” because the exception proves that such a rule already exists.
There’s a converse to this logic that I ran into repeatedly when designing themes: if a rule says a character can perform some action when they meet certain conditions, that implies they cannot perform that same action if they do not meet the conditions. For example, a handicapped parking sign means “you can only park here if you meet certain criteria”. In D&D as in life this is normally obvious and in fact the point of many rules: Improved Initiative lets a player add +4 to their initiative check, which they cannot do without the feat or an ability that acts similarly. A cleric can cast spells using Wisdom, and a wizard cannot unless they have an ability that says otherwise. And no rule is in place that says “a 9th-level fighter can hold a shield in each hand”, so we assume all characters can hold a shield in each hand as long as that’s not barred elsewhere (though they don’t get the AC from both, because of a rule).
But a writer can get into trouble by specifying something he or she shouldn’t. Consider the feat Research, from the 3.5E Eberron Campaign Setting. It allows a character to use a Knowledge check to search a repository of information, like a library. This would be fine if it let characters do it faster, or in a way they couldn’t. But it didn’t do that. It just said “you can use your Knowledge skills to extract information from books, scrolls, and other repositories of facts and figures.” It gave the characters rules for using libraries and similar repositories and left it at that. And in doing so it stripped the same ability from characters without the feat.
In a campaign where Research exists, characters cannot use libraries without it. If they could, the feat would not exist. The action is “research in a library” and the condition is “have this feat”. Publication of the feat retroactively stripped library access from any and all characters unless they met a condition that did not previously exist. It’s pretty goofy, and so far I’ve only met two kinds of DMs: those who don’t know about Research, and those who ignore it.
And there’s where I hit a wall with themes. I couldn’t say “a criminal with the shady friends ability can fence stolen goods” because that implies no other character can fence stolen goods. I couldn’t say “a celestial with the guilty conscience ability can sense when an action would cause them to violate their alignment” because that disallowed players and DMs from coming up with their own methods of doing the same. Any time I had a fun or flavorful application of a skill, I had to consider whether it was something the rules could already support or, more restrictively, whether it was something I would allow in my campaigns. If I would let a player use Appraise in a certain way without themes, I couldn’t justify allowing only characters with a theme to use Appraise the same way.
That’s why there aren’t a lot of theme abilities that deal with how PCs interact with NPCs. A lot of that is already allowed, or the DM’s responsibility, or too fun to restrict. I want themes to expand character options, not restrict gameplay options through implication.
It is possible to do this well. Consider the feat Master Manipulator, in the 3.5E Player’s Handbook II. It gives a character two abilities. The less interesting one is the ability to make a Diplomacy check to reduce the Listen, Sense Motive, and Spot checks of some nearby creatures. Normally this would be something a character can already do, but the penalty is -4, greater than the normal -2 penalty D&D recommends. It also defines the limitations of this ability so it serves as a reference point for players or DMs who want to do something similar. It’s not a major deal, but it’s something.
The one we care about is the second ability, and not just because of its amazing art. It boils down to this: if somebody lies to you, and you detect the lie with Sense Motive, and you succeed at a subsequent Diplomacy check versus the target’s Bluff, your circular conversational stylings trick the person into explaining what they lied about and why. It brings multiple skills together in a way that counts as a new application for both, and with an appropriately clever player and DM it can make for amazing at-table moments. The existence of the feat doesn’t ban a character from taking any otherwise obvious action. It’s just good.
It is, however, hard. November was about getting as many themes done as possible, not making them all fully-fleshed exemplars of the mechanic. I do want to go back and come up with ways to combine skills to create new play opportunities, balance them, and phrase them in a way in keeping with Paizo’s language and formatting. That just wasn’t in the cards this month.
I’ll continue working on themes but I won’t be nearly as head-down on them as I was (and the players in my campaign, who may have noticed that November was mostly sidequests and cancelled sessions, will thank me). I want to get a few more done, like the royal, the vigilante (remember, the stimulus for this whole exercise?), the planar traveler, and a few more mundane ones. Once I have a decent set of them I can get started on the second drafts, which is where I’ll spend more time on each ability to make sure it’s something worth taking.