It's a free descriptor system, and all abilities are rated from 1 to 20. (Scores above 20 cycle back round, but - in effect - get a free "hero point" expenditure every time which steps the result up by one (eg minor failure to minor victory, or minor victory to major victory). There are rules for managing broad vs narrow descriptors (eg "strong as an ox" vs "lifts heavy rocks") to ensure parity of utility, but that's explicitly based on considerations of (i) fairness and (ii) encouraging evocative descriptions even if they narrow the descriptor, not simulation.
The reason for keeping all descriptors rated on the same scale is much the same as the reason that AW or DW uses the same ranges for all resolution, with a maximum modifier (typically) of +3 or so: it makes the maths work. Just as one example: if my cowboy is racing back to the homestead to save his kid brother from the bandits, I might test my Care For My Kid Brother (which, let's say, is rated at 17), with an augment from my horse's Galloper (which, let's say, is rated at 12). The system doesn't use any sort of "simulationist" resolution, and doesn't care how fast the horse is going in mph. It cares about the salience of those descriptors, which are signalled by the number next to them.
Now my horse might have Galloper 12, while the hustler who is planning to win a bag of silver dollars in the local gift might have Sprinter 15. That doesn't tell us that the hustler - even if near-guaranteed to win the gift - is faster than the horse. It tells us that the fact that this guy is a sprinter is more salient in the fiction than the fact that my horse can gallop fast. And as I posted, the question of whether the hustler can outrun the horse isn't settled by making a check, but by considering genre-based credibility. An analogy to this in 4e would be something like the sealing of the Abyss that I described upthread; intimidating Orcus would be another example; or everyone's favourite hypothetical degenerate social action declaration, the PC who persuades the king to forfeit his/her throne (in 4e this fails credibility for a heroic PC, but in my view not at all for a paragon one!).
From DW, p 58:
Note that an “attack” is some action that a player undertakes that has a chance of causing physical harm to someone else. Attacking a dragon with inch-thick metal scales full of magical energy using a typical sword is like swinging a meat cleaver at a tank: it just isn’t going to cause any harm, so hack and slash doesn’t apply. Note that circumstances can change that: if you’re in a position to stab the dragon on its soft underbelly (good luck with getting there) it could hurt, so it’s an attack.
That's the "credibility test" at work. To pick some contrasting systems, AD&D and 3E D&D and Classic Traveller have nothing like this: in each case the player can declare the action, the check is made, and the result compared to the difficulty (ie the AC in D&D, the 8+ needed to hit in Traveller). Credibility is an output of the system (and it's a legitimate criticism of the system that it produces absurd outcomes, like a single linkboy with a dagger being able to one-shot a dragon: traditionally D&D uses hit points to handle this, while in Traveller some modifiers just make hitting impossible without a sufficiently high skill bonus).
Here's another example, from Ironsworn (p 208):
You might be familiar with roleplaying games that give various tasks a difficulty rating or modifier. The flexibility to make each toss of the dice contextual, to adjust the chance to succeed based on the situation, creates an experience which helps simulate your imagined reality.
However, the Ironsworn rules do not utilize fine-grained mechanics for the difficulty of a particular challenge or the abilities a foe can bring to bear. Instead, the requirements to overcome challenges in your world are primarily represented through your fictional framing. . . .
A leviathan is an ancient sea beast . . . It’s tough to kill because of its epic rank, and it inflicts epic harm, but it doesn’t have any other mechanical characteristics. If we look to the fiction of the leviathan’s, description, we see “flesh as tough as iron.” But, rolling a Strike against a leviathan is the same as against a common thug. In either case, it’s your action die, plus your stat and adds compared to the challenge dice. Your chances to score a strong hit, weak hit, or miss are the same.
So how do you give the leviathan its due as a terrifying, seemingly invulnerable foe? You do it through the fiction.
If you have sworn a vow to defeat a leviathan, are you armed with a suitable weapon? Punching it won’t work. Even a deadly weapon such as a spear would barely get its attention. Perhaps you undertook a quest to find the Abyssal Harpoon, an artifact from the Old World, carved from the bones of a long-dead sea god. This mythic weapon gives you the fictional framing you need to confront the monster, and finding it can count as a milestone on your vow to destroy this beast.
Even with your weapon at the ready, can you overcome your fears as you stand on the prow of your boat, the water surging beneath you, the gaping maw of the beast just below the surface? Face Danger with +heart to find out.
The outcome of your move will incorporate the leviathan’s devastating power. Did you score a miss? The beast smashes your boat to kindling. It tries to drag you into the depths. Want to Face Danger by swimming away? You can’t outswim a leviathan. You’ll have to try something else.
Remember the concepts behind fictional framing. Your readiness and the nature of your challenge may force you to overcome greater dangers and make additional moves. Once you’ve rolled the dice, your fictional framing provides context for the outcome of those moves.
Again, we see the credibility test at work. This can be contrasted with, say, Burning Wheel. In BW the leviathan would have Grey-shade Mortal Wound (ie numerically about double that of an ordinary mortal creature) and hence any normal weapon will at best have the chance to inflict a Superficial Wound. It would force a Steel check when confronted; and while its would-be harpooner is hesitating it would strike the boat using the Devastator trait to reduce it to kindling. In BW, unlike in HeroQuest, the numbers are "simulationist" measure of in-fiction capacity, sitting on a common scale; and unlike in Ironsworn or DW, the numbers provide the input into resolution with credibility being the output.
I'm not advocating for either approach; just noting the significant difference,
and my opinion that 4e D&D sits on the "subjective" side of the divide.
To move from description to advocacy: I think it is hard to make a game that uses "objective" difficulties and resolution
and produces a truly epic/mythic feel in play. I don't regard 3E as a success in this respect. BW pushes in this direction, but at least as I've experienced it has a natural tendency towards grittiness and details mattering. Whereas systems I know that do reliable gonzo are 4e D&D and MHRP/Cortex+ Heroic, and in both cases I think the "subjective" approach is part of this.
