I’m confused. Both Shield Mastery and Two Weapon Fighting use identical precondition language (“when you take the attack action”). You said you have to finish ALL attacks with the attack action first for Shield Mastery…don’t you have to do that with two weapon fighting as well? They don't have the same wording. Shield Master refers to the Attack action, whereas two-weapon fighting refers to making an attack with the Attack action.
— Jeremy Crawford (@JeremyECrawford) May 17, 2018
Crawford has lost his goddamn mind.
“If you take the Attack action on your turn, you can use a bonus action to try to shove a creature within 5 feet of you with your shield.”
…versus…
“When you take the Attack action and attack with a light melee weapon you are holding in one hand, you can use a bonus action to attack with a different light melee weapon that you’re holding in the other hand.”
~~~
When you…
1) …take the Attack action…
AND
2) …attack with a light melee weapon you are holding in one hand…
THEN
…you can use a bonus action to…
~~~
You cannot use Two-Weapon Fighting unless BOTH pre-conditions are met.
If you take the Attack action, but attack with something OTHER than a light melee weapon, or fail to attack at all (for example, performing a Grapple check), then you cannot use the bonus action for the extra attack.
Likewise, if you make an attack with a light melee weapon, but do so as an Opportunity Attack, or as part of Casting A Spell, you also cannot use the bonus action for the extra attack.
~~~
To achieve the interpretation Crawford suggests, you would have to write the rule differently.
“When you attack with a light melee weapon you are holding in one hand AS PART OF the Attack action….”
This version of the rule takes the two separate and distinct pre-conditions, and replaces them with a single combined pre-condition.
~~~
However, since that is NOT how the rule is written, that is not what it actually says or does! The RAW clearly denotes two separate pre-conditions, which must both be met independently of the other!
Fulfilling the 2nd pre-condition…
…attack with a light melee weapon you are holding in one hand…
does not automatically fulfill the first pre-condition!
One must separately…
…”take the Attack action”
And according to Crawford’s interpretation, you must make finish ALL attacks granted by the Attack action before you are considered to have “taken” it.
I am with D Walker 100%.
Crawford’s definition of “taking the attack action” is not held consistent.
I can’t figure out how he doesn’t see this.
His interpretation for TWF should be how shield master is read as well.
Then talk to your DM, or if you ARE the DM, use it the way you want.