I’m going to think aloud here about the breadth of skill in Fate, and a possible way to model verisimilitude in settings that suggest so.
Back in Spirit of the Century, there was a little idea of stunts that could modify skills — namely, that the Medical Attention stunt could make the Science skill also a skill about medicine and so on. It’s something we touch on in Dresden, and in Fate Core, but lately I’ve been wondering more and more about it.
On one hand, the purpose of that is important: it keeps the skill list from getting bloated. The skill economy is tight by design, so just piling atop more skills turns it into something cumbersome — like the GURPS skill list, but without the underpinning such a system requires. The Fate skill system also is about economy of a game’s anticipated actions, which is another reason to not increase the bloat — each skill brings with it its own set of things to potentially overcome or advantages to content with.
But here’s the thing: this works in a pulp setup, where a sense of verisimilitude isn’t as desired. But in a case where it is, then you would have characters who were good at medicine but not a science. Or good at driving, but not piloting an airplane. Or good at mathematics & cryptology, but not mechanics, etc. So having them as stunts off of a skill is an option that doesn’t represent such situations.
Here’s a thought I’ve been kicking around as a compromise: the Expertise Skill. It’s a build on an existing skill that’s not exactly covered in the original version, like medicine in Science. You can either take that skill in lieu of the original (thus preserving the skill economy), or you can take a stunt from the base skill that gives you access to that other skill (as we’ve already seen in Fate builds). And because it’s not a core skill, it’s not a detractor to have it.
Furthermore, someone with a high-enough skill could (to borrow from GURPS) default to the other: if you have at least Good in a base skill, you can attempt an Expertise skill at Average — and vice versa. This isn’t -2, but a flat Average, whether your skill is Good, Great, Superb, etc. This helps with some of the bloat effect, because the skill is technically accessible, just not with proficiency, to a wider net of characters. (And possibly a toggle that could be turned off for a given expertise.)
Let’s say I’m working on a WWII build of Fate with military, intrigue, etc. Clearly, I’d rename Crafts to Mechanics, cuz. But that world is one where being able to tinker with an engine or radio doesn’t convey, say, cryptology and cryptanalysis. Sure, that won’t come up often, but it’s not inconceivable. So, what if Mathematics was an expertise skill based on Mechanics? It could be built as its own thing, and either taken as a replacement for Mechanics or as a stunt. Each to say “here’s the Overcome, Create an Advantage, Attack, and Defense elements” for one.
Here’s where it becomes, to me, a non-trivial problem: the example I gave is both boring from a player-character standpoint and exactly what I’m thinking of. But the stories where such a character exists is non-zero, and there’s where verisimilitude comes into play: NPCs could be very easily created with these in mind. Having to rescue a cryptologist, or having to recruit one, could be a story element. But once you enter that in, you introduce the idea of a character saying “I also want to play a cryptologist investigating the horrible unknown, because he’s seen something in numbers that is unsettling but also unignorable.” Which then turns the idea into a potentially compelling PC, suddenly enabled by the broaden skill set to viably be such a character — one that would have been surely shoehorned to fit into a compromise otherwise.
Thus, this post. Creating a situation in Fate that extend the range of fictional actions within skills, when appropriate to the stories that could be told, without extending a sense of bloat. The same could be done for Drive/Pilot/Sail, etc., though you could just as well not.
One question that would come up is whether the added skill access is worth a stunt. And I suspect that is the litmus test for whether the expertise skill is valid, though it’s possible that you could leave the decision in the hands of those playing the game. Plus, much of the time, if someone were to say “can my skill do X?” and it would be a hell of a stretch to do so, I reply with “sure, just take a stunt for it.” Thus, the range of fictional actions are already that broad, just in the nebulous space that is the stunt system. Something I hadn’t realized in a cohesive sense until I wrote this post.
In any case, this is an rectify a case presented by the original concept: using stunts in this manner is about character who are more competent, but doesn’t model those differently competent. We’ve always been able to model a medic who is a brilliant scientist or a cryptologist who is a brilliant mechanic, but not so much if you change that to “who isn’t a…”
Okay, I think I have successfully chased my tail on this, so time for a second (and third, etc.) opinion. What do you Fate-heads out there think?
 You could argue that the GURPS skill list is too bloated, sure, but the system around skills is built partly with that in mind. Fate isn’t by default.
 As I’m typing this, The Princess Bride is playing.
 After sleeping on this, I have another thought regarding this specific example. However, the broader concept might still have merit, so it’s still worth my exploration.