In the latest FATE Core draft when describing extras a "permission aspect" is often referenced, as are a concept of extra "costs". However, it is unclear whether the permission itself is a cost (some examples seem to indicate this) or it is separate (the extra cost page seems to indicate this). So is an permission a cost, and in particular should a game in which all characters would have a permission aspect increase the number of aspects?
It's tricky, but--no, permissions are not usually costs.
Costs are more restrictive than permissions, and bonus aspects would only really be justified in a game where the extras use aspects as a cost, not just as a permission.
I think it is worth delving into the theory a bit, with quotes, because this is a elegant concept: narrow but deep.
A permission is narrative justification
And it may or may not include a mechanical component.
[Y]ou establish permission to take an extra with one of your character’s aspects, which describes what makes your character qualified or able to have it. You can also just agree it makes sense for someone to have an extra and call it good. (Fate Core 274)
If we're familiar with the Dresden Files RPG, we'll recognize the idea of permissions as being a version of the relationship between a character's High Concept aspect and the supernatural powers he can take:
No supernatural ability may exist in a vacuum--it must come about due to specific reasons rooted in your character’s concept. At the very least, this usually means that the supernatural abilities must clearly derive from your character’s high concept[...] (Your Story 158)
One of the main reasons for doing this is outlined in a sidebar on the same page:
[Y]ou gain all of the benefits of having an aspect riding shotgun whenever the character’s supernatural abilities are in use.
So we want to be sure the extra has narrative justification, and it's best when there's a reliable way to attach Fate point expenditure to the extra's use. That's what a permission is about.
A cost is a balancing resource expenditure
It is explicitly mechanical:
A cost is how you pay for the extra, and it comes out of the resources available on your character sheet, whether that’s a skill point, a refresh point, or an aspect slot.
Because extras provide bonus mechanical power, and Fate is concerned about generic character balance, that power must be offset by some expenditure of resources.
Clearly both permissions and costs can be achieved through the use of aspect slots, but there seems to be a philosophical difference between using an aspect slot as a permission and using it as a cost.
Let's look at some examples in the Core.
Aspect as permission
The Collegia Arcana Magic extra (FC 275) uses aspects for permission.
Permissions: One aspect reflecting that you’ve been trained by the Collegia
This doesn't dictate my aspect, just defines it broadly. I could be a Barely-Trained Orphan Talent or a Moor of the Penultimate Rank and equally qualify. I can still craft the aspect to reflect depth and subtly within the character so that it could be invoked in ways that don't really involve the Collegia at all ("Orphan" and "Moor" respectively, in my examples).
Aspect as cost
The Galerider (FC 286) has no permission: its existence is crucial to the game itself (I might consider its permission to be a setting or campaign aspect, if I wanted to be a stickler for permissions).
Permissions: None, understood as part of the game’s conceit.
However, she's got a cost in aspects.
Costs: Skill ranks, refresh, and aspect slots, invested by several characters.
Aspects: Fastest Ship in the Fleet, Hidden Cargo Compartments, Lord Tamarin Wants To Sink Her
Please notice that in this case, where aspects are a cost, they are laid down explicitly. I don't get to fiddle with a cost aspect so that it has widespread implications for my character beyond the extra it's permitting: a cost aspect is narrow in scope, dedicated entirely and solely to the extra it's paying for.
Aspect as permission and cost combined
Brace Jovannich’s Dueling Pistol (FC 281) is weird, but hammers home the difference between permissions and costs.
Permissions: Possessing the aspect, The Legacy of Brace.
Costs: One aspect slot (for the permission aspect) and one point of refresh.
Here, the permission aspect is explicitly also a cost. And look! It's precisely delineated and narrow in scope, giving little room for invokes unrelated to the extra it pays for.
Thus, costs are more restrictive than permissions.
Bonus resources are better in games with cost aspects
As we just saw, an aspect being spent as a cost can't be easily invoked in contexts that don't feel the extra's influence, while permission aspects can be crafted in a way that they're invokable in a broader manner.
This means that in most cases, a game in which all characters would have a permission aspect is okay --but if the aspect is instead or also a cost, then we do well to "raise the number of slots all PCs get at character creation to accommodate extras" (FC 274).
As I understand it, a permission can be a cost, but not necessarily so. A permission is primarily a justification of why you have the extra, whereas a cost is a character-building resource (aspects, skills and stunts) you have to spend in order to benefit from the extra.
Some of the permissions are not costs. From one of the examples, it doesn't make sense to have a magic sword as an extra unless you actually have the magic sword. Permissions like this don't cost you anything in terms of using up character-building resources.
But some of the permissions are also costs - things you need to have spent your character-building resources on in order to gain that extra. From another of the examples, you can't benefit from having a famous gun without having an aspect based on it. The aspect is the gun (you have the gun, making it a permission), but the gun itself is also an aspect (one of your character-building resources you've spent, making it a cost - you don't have that aspect available to define something else about your character), so it can be compelled and invoked. (This example also costs a point of refresh, to reflect it's stunt-like ability).
Other example permissions seem similar to the second case, such as not being able to use magic without an aspect indicating training from a school of magic. However, in this case, you can name this aspect yourself to indicate something else about your character as well - you have freedom to define your aspect - so it is not a cost.