I was working on a Rogue/Artificer multiclass for one of the Class Throwdowns in the Tips & Tactics board, and I noticed that Artificer eventually gets blanket expertise in all tool proficiencies and, prior to that, the only tool that was eligible for Expertise was Thieve's Tools. A generous interpretation of the rules says to me that a character who chooses to take expertise in Thieve's Tools as a Rogue and also gains Tool Expertise from Artificer would get to add their proficiency bonus at least 3 times to rolls.
Obviously, I don't think that's how it's intended to be read. I tried to look it up, but there doesn't seem to be an easy-to-find blanket ruling on Expertise from multiple sources... within Rogue or Bard where Expertise can be taken multiple times the wording is such that you can't even attempt to select the same skill multiple times for expertise, and the Skill Expert feat explicitly calls out that it can't be applied to skills that gain expertise (or any equivalent ability) from another source. But when taking Expertise from Rogue there's nothing that says you can't apply Expertise to a skill that already has expertise from Bard.
Anyway, I was wondering if I'm just not finding the specific ruling about the subject. Maybe the wording itself is actually precise enough to preclude this... sort of like how Extra Attack doesn't stack because it doesn't say that you gain an additional attack, but rather that your attack action is replaced with a specific number of attacks. Expertise doesn't say that you add your proficiency a second time, but rather that the proficiency is doubled.
I'm not really trying to defend the idea of combining expertise, I'm mostly just wondering if this has ever come up at anyone's table.
Expertise doesn't stack, you only get to have it once, just like with other class features. If you get the same feature from multiple sources then you don't get them both. So a level 5 fighter gets extra attack, a level 5 barbarian gets extra attack, but a level 10 (fighter 5 / Barb 5) character only gets one extra attack not both. This is the same across the board with bonuses and penalties. Temp hit points don't stack, Bless from 2 different casters don't stack and so on. It is just bad wording really, but it should be obvious to most that if a bard cannot take expertise in something he already has expertise in from his rogue class, then he same would apply in reverse.
"Your proficiency bonus can't be added to a single die roll or other number more than once."
"Occasionally, your proficiency bonus might be multiplied or divided (doubled or halved, for example) before you apply it. For example, the rogue's Expertise feature doubles the proficiency bonus for certain ability checks. If a circumstance suggests that your proficiency bonus applies more than once to the same roll, you still add it only once and multiply or divide it only once."
This is the general rule that prevents all the abilities that can add your proficiency bonus twice to various abilities (and which are NOT all called expertise - like the Knowledge cleric bonus to two skills) from stacking with each other.
Expertise doesn't stack, you only get to have it once, just like with other class features.
It seems like splitting hairs I know, but these are different features in play. People confuse this rule all the time thinking it means you can't gain the same effect from different features, but the rule doesn't care about effects, just the feature itself.
Tool Expertise does not grant a feature called "Expertise". It allows you to double your proficiency bonus for a check that uses your proficiency bonus. But as David42 quoted, you can only double your proficiency bonus once regardless of what features you have.
I was working on a Rogue/Artificer multiclass for one of the Class Throwdowns in the Tips & Tactics board, and I noticed that Artificer eventually gets blanket expertise in all tool proficiencies and, prior to that, the only tool that was eligible for Expertise was Thieve's Tools. A generous interpretation of the rules says to me that a character who chooses to take expertise in Thieve's Tools as a Rogue and also gains Tool Expertise from Artificer would get to add their proficiency bonus at least 3 times to rolls.
Obviously, I don't think that's how it's intended to be read. I tried to look it up, but there doesn't seem to be an easy-to-find blanket ruling on Expertise from multiple sources... within Rogue or Bard where Expertise can be taken multiple times the wording is such that you can't even attempt to select the same skill multiple times for expertise, and the Skill Expert feat explicitly calls out that it can't be applied to skills that gain expertise (or any equivalent ability) from another source. But when taking Expertise from Rogue there's nothing that says you can't apply Expertise to a skill that already has expertise from Bard.
Anyway, I was wondering if I'm just not finding the specific ruling about the subject. Maybe the wording itself is actually precise enough to preclude this... sort of like how Extra Attack doesn't stack because it doesn't say that you gain an additional attack, but rather that your attack action is replaced with a specific number of attacks. Expertise doesn't say that you add your proficiency a second time, but rather that the proficiency is doubled.
I'm not really trying to defend the idea of combining expertise, I'm mostly just wondering if this has ever come up at anyone's table.
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Expertise doesn't stack, you only get to have it once, just like with other class features. If you get the same feature from multiple sources then you don't get them both. So a level 5 fighter gets extra attack, a level 5 barbarian gets extra attack, but a level 10 (fighter 5 / Barb 5) character only gets one extra attack not both. This is the same across the board with bonuses and penalties. Temp hit points don't stack, Bless from 2 different casters don't stack and so on. It is just bad wording really, but it should be obvious to most that if a bard cannot take expertise in something he already has expertise in from his rogue class, then he same would apply in reverse.
If you want the explicit rule. PHB p173-174
"Your proficiency bonus can't be added to a single die roll or other number more than once."
"Occasionally, your proficiency bonus might be multiplied or divided (doubled or halved, for example) before you apply it. For example, the rogue's Expertise feature doubles the proficiency bonus for certain ability checks. If a circumstance suggests that your proficiency bonus applies more than once to the same roll, you still add it only once and multiply or divide it only once."
This is the general rule that prevents all the abilities that can add your proficiency bonus twice to various abilities (and which are NOT all called expertise - like the Knowledge cleric bonus to two skills) from stacking with each other.
It seems like splitting hairs I know, but these are different features in play. People confuse this rule all the time thinking it means you can't gain the same effect from different features, but the rule doesn't care about effects, just the feature itself.
Tool Expertise does not grant a feature called "Expertise". It allows you to double your proficiency bonus for a check that uses your proficiency bonus. But as David42 quoted, you can only double your proficiency bonus once regardless of what features you have.
My homebrew subclasses (full list here)
(Artificer) Swordmage | Glasswright | (Barbarian) Path of the Savage Embrace
(Bard) College of Dance | (Fighter) Warlord | Cannoneer
(Monk) Way of the Elements | (Ranger) Blade Dancer
(Rogue) DaggerMaster | Inquisitor | (Sorcerer) Riftwalker | Spellfist
(Warlock) The Swarm