Bonus Is the Ability Score
Unless you are playing one of the twenty-sided variants that actually use the 3-18 standard six, you don’t need the numerical part of your ability score.
In modern, mainstream D&D (this includes Pathfinder, too), the only part of your score that matters is the modifier. So why bother with the 3-18 part?
The ability score creation process for D&D and Pathfinder is convoluted. You stack up bonuses on on one number to derive the actual number you will use once dice hit the table. The number you don’t use takes up space on your character sheet, and competes with the number you do use.
Just call the bonus the ability score and be done with it.
Decide how you want ancestry or racial or species bonuses to affect the scores, and then decide how ability advancement happens and you are good to go.
Scrashnow's Twenty-sided World 