Ability scores.
Alternatively, ability scores are not determined independently, but are determined by your choice of class, race, trained skills, feats, etc. Moreover, ability scores will have little or no mechanical effect and become mostly descriptive. All mechanical bonuses are dependent on the player's choice of race, class, trained skills, feats, and other discretionary bonuses.
For example, being a fighter gets you bonuses in Strength and Constitution. Training in Diplomacy gets you a bonus to Charisma, while Improved Initiative grants a bonus to Dexterity.