Does the damage bonus from the new UA "Thrown Weapon Fighting" fighting style stack with that of the "Dueling" fighting style?

Question

The description of the Dueling fighting style (on PHB p. 72, and in other class descriptions) says:

When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon.

The description of the thrown weapon property (PHB p. 147) says:

Thrown. If a weapon has the thrown property, you can throw the weapon to make a ranged attack. If the weapon is a melee weapon, [...]

The new UA, Class Feature Variants, adds a new fighting style option called Thrown Weapon Fighting:

You can draw a weapon that has the thrown property as part of the attack you make with the weapon.

In addition, when you hit with a ranged attack using a thrown weapon, you gain a +1 bonus to the damage roll.

Does the Thrown Weapon Fighting fighting style grant a +1 to the damage of daggers when you throw them one at a time?

In this question, it was answered that thrown weapons can get the +2 damage bonus from the Dueling fighting style. So if I have both the Dueling and Thrown Weapon Fighting fighting style, would I then have a +3 bonus to my damage rolls if I throw one dagger at a time?

Answer 1

It is 100% dependent on whether you think the Dueling Fighting Style applies to thrown weapons; a question already discussed elsewhere

If Dueling Fighting Style doesn't apply to thrown weapons then clearly these never stack as the Thrown Weapons Fighting Style requires a thrown weapon. Below I will show that if the Dueling Fighting Style does apply to thrown weapons then they do stack. Seeing as how the question about whether the Dueling Fighting Style applies to thrown weapons already exists, and answers argue both ways, there's no real reason to answer that question here.

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The Dueling Fighting Style states:

When you are wielding a melee weapon in one hand and no other weapons, you gain a +2 bonus to damage rolls with that weapon.

The only relevant thing this requires is that we attack with a melee weapon.

And the Thrown Weapon Fighting Style states:

You can draw a weapon that has the thrown property as part of the attack you make with the weapon.

In addition, when you hit with a ranged attack using a thrown weapon, you gain a +1 bonus to the damage roll.

This requires a weapon with the thrown property, and that we make a ranged attack using said weapon. The thrown property shows that a melee weapon, when thrown, is making a ranged attack:

If a weapon has the thrown property, you can throw the weapon to make a ranged attack [...]

All we need to do then is throw a melee weapon with the thrown property and we would benefit from both Fighting Styles.

Note that these do not add together when using a dart (or technically a net, but that has no damage roll anyhow) as they are ranged weapons with the thrown property, so Dueling can't apply.

I see no reason that the damage bonuses wouldn't stack, the only thing you cannot add twice to a roll (as far as I'm aware) is your proficiency bonus:

Your proficiency bonus can't be added to a single die roll or other number more than once.

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A small note on wording:

The Thrown Weapon Fighting Style technically only requires a weapon with the thrown property if you're drawing it. The damage bonus applies to any ranged attack using a thrown weapon. This means that technically it applies to ranged improvised weapon attacks as well:

[...] An improvised thrown weapon has a normal range of 20 feet and a long range of 60 feet.

Note, however, that the Dueling Fighting Style would not apply because improvised weapons do not have the melee or ranged properties, they simply are weapons used to make melee or ranged attacks.

Answer 2

Yes, they should stack

Dan Dillon tweeted a question to rules designer Jeremy Crawford in 2015 (before Dillon was hired by WotC himself):

Does the Dueling Style apply its bonus to a thrown melee weapon?

JC answered simply: "Yes."

In 2016, another user asked JC a similar question:

Can the Dueling style bonus damage still works on melee weapons that are thrown?? Let's say a Handaxe for example.

The response from JC was:

The Dueling fighting style works with a thrown melee weapon. The feature doesn't limit itself to melee attacks.

So if a thrown melee weapon is allowed to have the bonus from the Dueling fighting style, the Thrown Weapon Fighting fighting style should stack with the attack.

Jeremy Crawford's tweets are no longer official rulings, but they can provide a good source of rules intent.