Skill level Easy Average Hard Very Hard Base-6 -- -- -- 1/8 Base-5 -- -- 1/8 1/4 Base-4 -- 1/8 1/4 1/2 Base-3 1/8 1/4 1/2 1 Base-2 1/4 1/2 1 2 Base-1 1/2 1 2 4 Base 1 2 4 7 Base+1 2 4 7 11 Base+2 4 7 11 16 Base+3 7 11 16 22 Base+4 11 16 22 28 Base+5 16 22 28 35 Base+6 22 28 35 42 Base+7 28 35 42 50 Base+8 35 42 50 59 Base+9 42 50 59 69 Base+10 50 59 69 80
In general, I refer to "generalized maneuvers" as Specializations, although various different skills may also use other terms (Rituals for specializations in ritual magic, for instance). As a rule-of-thumb, most Specializations are Average ("World War II" is an Average Specialization of History skill, for instance), but some are Hard ("European History" as a Specialization of History skill). There also exist Easy Specializations; as one might expect, their cost is "one step" cheaper than Average Specializations (the first level costs 1/4 point, the second costs 1/2 point, the third costs 1 point, the fourth costs 2 points, the fifth costs 4 points). An example of Easy Specializations is (most) specific alchemical formulae in the variant alchemy system I'm working on. Also, there are some cases where Specializations cannot be used unless they have been specifically learned (such as those same alchemical formulae). Also, as a general rule, no more than 5 levels may be bought of any one Specialization (4 points in an Easy one, 6 points in an Average one, or 8 points in a Hard one).
So the simple rule is, base each skill roll on whatever attribute seems most appropriate at the time. Many skills will still have almost all of their rolls against the same attribute, though.
I also allow individuals to have Group Skill Bonuses, as opposed to reserving that for races. And I've generalized those bonuses a bit: One can have a Group Skill Bonus for any skill group, but "Combat" skills are split between the Melee Skill Group and the Missile Skill Group (it's rather self-evident which skills should belong where), and bonuses in these groups must be bought separately. Also, I've ditched the "Language Talent" and "Musical Ability" advantages in favor of treating both as skill sub-groups (so you can buy bonus with either languages or music at 3 points per +1, max 9 points for +3).