Do ability modifiers from the same ability stack? For instance, can you add the same ability bonus on the same roll twice using two different effects that each add that same ability modifier?
No. An ability bonus, such as "Strength bonus", is considered to be the same source for the purpose of bonuses from the same source not stacking. However, you can still add, for instance “a deflection bonus equal to your Charisma modifier” and your Charisma modifier. For this purpose, however, the paladin's untyped "bonus equal to her Charisma bonus (if any) on all saving throws" from divine grace is considered to be the same as "Charisma bonus (if any)", and the same would be true for any other untyped "bonus equal to her [ability score] bonus" constructions.
Dragon Ferocity and Tiger Claws: These feats both tell me to add 1/2 my Strength bonus to damage. How does that affect my damage? Does that reduce down to 1/2?
No, Dragon Ferocity should read "While using Dragon Style, increase your Strength bonus on unarmed strike damage rolls by an additional one-half your Strength bonus, to a total of twice your Strength bonus on the first attack and 1-1/2 your Strength bonus on the other attacks" and Tiger Claws should read "If you use Power Attack in conjunction with this attack, increase your Strength bonus on one of the damage rolls by an additional one-half your Strength bonus, normally to a total of 1-1/2 your Strength bonus." These changes will be reflected in future errata.
第一条的意思是一个属性调整值值不会上一个加值两次
第二条的意思是虎爪和龙威都是调整力量上伤害的倍率，其实质依然是一次属性上调整值，所以可以加起来
而弩手和铳士则不同，他们是分别敏捷上伤害了。所以不叠
