Does two weapon fighting's qualifying "attack" have to be part of the "Attack" action?

Question

The rules for two-weapon fighting state:

When you take the Attack action and attack with a light melee weapon that you're 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.

Emphasis mine. Now, under most circumstances you would wield two light melee weapons, attack with at least one of them during your Attack action, and attack again as a bonus action. However, the rules themselves just say "take the Attack action and attack with a light melee weapon", not specifically "take the Attack action to attack with a light melee weapon" or "attack with a light melee weapon during an Attack action".

In other words, both the requirements "took the Attack action" and "made an attack with a light melee weapon held in one hand" need to be met during a turn, but the light melee weapon could be used to attack separately from the Attack action. Is that correct?

An example for how to accomplish this: An Eldritch Knight Fighter takes the booming blade cantrip and the Dual Wielder feat. That Fighter takes the Attack action, attacking with a Greatsword, then uses Action Surge to take an additional action. He drops the Greatsword (everything I've seen indicates that dropping a weapon doesn't even require an object interaction), then draws two light melee weapons as permitted by Dual Wielder. For the second action, the Fighter casts booming blade (SCAG, p. 142) which states:

As part of the action used to cast this spell, you must make a melee attack with a weapon against one creature within the spell’s range

Thus, after those two actions the Fighter would have both taken the Attack action and made an attack with a light melee weapon in the same turn, and I would expect he could use two-weapon fighting to make a bonus action attack with the weapon not used during booming blade.

Note that this scenario is just an example; I'm not 100% certain there's a way to cast booming blade while holding two melee weapons, but I know there are other ways to make an attack outside of the Attack action and I just couldn't find one quickly that was more definitively possible.

Answer 1

The attack must be made as part of the Attack action

I can see your reasoning, but at the very least that goes against what I believe the intent of the wording is. The obvious reading of the rule is that you attack with the Attack action using a light melee weapon, then you can use your bonus action to make another attack with your other light melee weapon.

---

The rule you're referencing:

When you take the Attack action and attack with a light melee weapon that you're 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.

I read this to mean that they must both be done at the same time. You have mentioned other ways this could have been worded to achieve this intent that would not provide you with your loophole (Action Surge and Booming Blade, etc) but this is the wording they went with, and I believe their intent was for "and" to mean "both of these things must be done as one action", although it doesn't explicitly say that.

---

Although not exactly about this, Jeremy Crawford has said the following, which broadly covers my reasoning presented here:

In any piece of writing, context matters. If a rule has multiple sentences, they're meant to be read together. For example, the first sentence of Divine Sense is meant to be read with the rest of the feature's sentences, which explain that first sentence.

Hence when you take the Cast a Spell action instead of the Attack action to make the melee attack with a light weapon, that does not satisfy the "and" part of that clause.

Without clarification on this exact issue from a designer, this is probably the best I'm going to be able to conclude.

Answer 2

This interpretation makes the rule make no sense

You are trying to read this as Attack and attack with a light melee weapon as two separate independent conditions that have to be met. However, if you assume this reading to be correct, it makes the rule make no sense.

To illustrate why, let's look at an example of an ability that we know for sure has multiple independent conditions that must be met:

Pounce. If the lion moves at least 20 feet straight toward a creature and then hits it with a claw attack on the same turn, that target must succeed on a DC 13 Strength saving throw or be knocked prone.

Note that the pounce attack has two conditions: move and hit with an attack, but, vitally, the ability specifies the two conditions must happen on the same turn.

Now let's look at your reading of Two-Weapon Fighting in this same light:

When you take the Attack action and attack with a light melee weapon that you're 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.

By your reading there are two independent conditions: taking the Attack action and attacking with a light melee weapon. However, where is the part that specifies during what time period these conditions must be met? There is none.

By your reading, I could take the Attack action and then 10 turns later make an attack with a light weapon and I would still qualify for the TWF bonus attack.

The obvious reading of this rule has no such issues since lumping in the light melee weapon attack with the Attack action by definition means they have to be on the same turn as part of the same action.

So, we can argue that since your reading makes the rule make no sense, while the other, more obvious meaning seems to work as intended that your reading is not the correct one.

Rules as Intended also disagree with your reading

Jeremy Crawford says:

The precondition for using two-weapon fighting (PH, 195) is making an attack with the Attack action, so if you make an attack with the Attack action, you can now take the bonus action.

Note specifically that Jeremy says there is only one condition for two-weapon fighting. Your interpretation says there must be two. Also, Jeremy states that that one condition is making an attack with the Attack action. He does not say that the condition is making an Attack and then making another attack with a light melee weapon.

Jeremy Crawford also says:

In two-weapon fighting, you don't get the bonus attack unless the first attack was with a light melee weapon.

In your example your first attack was made with a Greatsword which is not light and thus does not qualify by that measure either. This also implies that the Attack and the light melee weapon condition are one and the same and part of the same action.