How does the Bladesinging wizard's Extra Attack feature interact with the additional Attack action from the Haste spell?

Question

The Bladesinging arcane tradition for wizards (TCE) gains the Extra Attack feature at level 6, whose description states:

Starting at 6th level, you can attack twice, instead of once, whenever you take the Attack action on your turn. Moreover, you can cast one of your cantrips in place of one of those attacks.

The haste spells allows the target to take an extra action on each of its turns for the spell's duration, with certain limitations:

That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

Say a Bladesinging wizard is under the effect of a haste spell.
Can the Bladesinger replace the single attack from their additional Attack action (from haste) with a cantrip cast, per the second part of their Extra Attack feature?

Answer 1

Neither rule is more specific than the other. The restriction "one weapon attack only" is written on a specific spell. The option "cast one of your cantrips in place of one of those attacks" is written on a specific class feature. There is no written guidance about the interaction.

I think we are in rulings territory, and I would rule on the side of balance concerns due to how cantrips scale. That is, I would rule against allowing the Hasted Attack action attack to be switched out for a cantrip.

An additional scaling cantrip per turn is equivalent power boost to a whole Attack action (with any Extra attacks or riders). The restriction in the Haste spell looks set to avoid that for martial characters, so it makes sense to keep the same regard for balance when looking at the Bladesinger feature. The bladesinging feature is already very good for overall damage, and the Haste spell a popular choice for Bladesingers because it is also already very good. It doesn't need this further boost.

Answer 2

You can make a single weapon attack with Haste

Let's look at your quoted text for Bladesinger:

Starting at 6th level, you can attack twice, instead of once, whenever you take the Attack action on your turn. Moreover, you can cast one of your cantrips in place of one of those attacks.

This feature does NOT say you can cast a cantrip with any extra attack, it says you can cast a cantrip instead of one of those attacks.

Then let's look at Haste:

That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

This specifically says one weapon attack only. So no, you can't re-apply the extra attack bladesinger feature here. And since you can't, you also can't apply the cantrip ability. (Needs 2 attacks to qualify for the cantrip)

Answer 3

Specific Beats General: "One Weapon Attack Only"

The Bladesinger is less specific because it is talking about any generic Attack action, be it the action of the turn or from an action surge (if multiclassed fighter) or what have you. The Bladesinger feature reads "whenever you take the Attack action on your turn." That is less specific than the restrictions added by the haste spell, which is "That action can be used only to take the Attack (one weapon attack only)." The haste spell is talking expressly about restrictions it is placing on this one specific new Attack action granted by the spell effect, so its restrictions, including "one weapon attack only," are more specific.

specific is defined:

Specifying; definite, or making definite; limited; precise; discriminating; as, a specific statement. [1913 Webster]

The this one single extra attack granted under this spell is clearly a more limited, and more precisely defined restriction or rule than a blanket all Attack action you take on all of your turns.

Like CSS

If you do any web development, you can think about specify the as if it were Cascading Style Sheets. You'd write the rule for Extra Attack targeting all Attack actions something like this (if these were CSS properites):

.Attack-action {...}

And you'd write the haste rule more specifically to catch just the hasted ones:

.Attack-action#haste {...}

Cantrip isn't a Weapon Attack

The Extra Attack of Bladesinger subclass doesn't turn the cantrip into a weapon attack, it only permits it as part of a attack normally. The extra restriction isn't subverted; thus you cannot use a cantrip on the hasted action because it isn't a weapon attack. Similarly, shove and grapple are also excluded by the restriction on the hasted action, even though they normally are options for an attack action.

Answer 4

I'd say that, for RAW, this is a case of specific beats general rule. All Bladesinging Wizards of 6th level can attack twice instead of once when taking the Attack action and can replace one attack with a cantrip. But only Bladesinging Wizards under the effect of Haste spell may take another action that can be an Attack action, limited to one weapon attack. I would conclude here that the spell is more specific than the class feature and the text of the spell allows for only a weapon attack. So no cantrip here.

Answer 5

It's allowed.

Since, in general, spells in 5e only do what they say they do, and no more or less, we should consult the wording of the spell. The Haste spell reads as follows:

That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

It does not disallow the use of the Extra Attack feature, merely restricting you to a single attack. That single attack can then be replaced by a Cantrip using the Bladesinger's Extra Attack feature.

Answer 6

Specific beats general, the Bladesinger can use a cantrip

There are many rules in D&D, and many effects that overrule those rules. The rules instruct us that specific beats general:

This book contains rules, especially in parts 2 and 3, that govern how the game plays. That said, many racial traits, class features, spells, magic items, monster abilities, and other game elements break the general rules in some way, creating an exception to how the rest of the game works. Remember this: If a specific rule contradicts a general rule, the specific rule wins.

Exceptions to the rules are often minor. For instance, many adventurers don’t have proficiency with longbows, but every wood elf does because of a racial trait. That trait creates a minor exception in the game. Other examples of rule-breaking are more conspicuous. For instance, an adventurer can’t normally pass through walls, but some spells make that possible. Magic accounts for most of the major exceptions to the rules.

In this case we must consider what is normal, and then what is changing the rules.

The simplest case

Consider a normal goblin. On the goblins turn they get 1 Action. If they use that Action to take the Attack action they get to attack once. If this goblin was Hasted, then they get a second Action, with which they can attack once more. I would consider this the most basic case.

Note that you can normally use your attack action to grapple or shove, but Haste only lets you make one "weapon attack", so you aren't allowed to use the free action to use these special attacks. Since these actions are available to all creatures, I would say that Haste overrules this general rule with its specific language.

A more complex case, but also quite common

The Attack action mentions another special case that overrules the normal rules;

Certain features, such as the Extra Attack feature of the fighter, allow you to make more than one attack with this action.

This situation is common enough that it is even mentioned within the action. Not just fighters get it, Barbarians, Monks, Paladins, and Rangers - as well as the College of Swords Bard, the Bladesinger Wizard, and the (unofficial) Blood Hunter. Not just that, many monsters also have Multiattack, which is essentially Extra Attack but for monsters. If you are playing D&D at midlevel or higher, you probably have a least one person in your party who has Extra Attack, and are fighting against monsters that have Multiattack.

A level 5 Fighter has Extra Attack, so if they were hasted then I believe the specific language of Haste would prevent them from using both their attacks. Generally the fighter could attack twice, but not when using Haste to take the Attack action.

The rare case

Now we come to Bladesinging. Bladesinger's Extra Attack is unique, no other Extra Attack is like this, nor is any Multiattack. It has two clauses:

You can attack twice, instead of once, whenever you take the Attack action on your turn. Moreover, you can cast one of your cantrips in place of one of those attacks.

The use of the word "moreover" may make this unclear to readers who aren't native English speakers. The word means "additionally". So when the Bladesinger uses the Attack action they can attack twice, and they can cast a cantrip in place of one of those attacks.

This is where things get extremely ambiguous.

Is Bladesinger specific enough to override Haste?

Bladesinger is an extremely niche case. Haste is a common spell, and seems to be written to interact with other common elements like Extra Attack, Multiattack, Shove, and Grapple. I don't see a reason to think that Haste should be able to overrule the second half of Bladesigner's Extra Attack since it is so unique.

Can you still use Extra Attack?

Haste doesn't disable Extra Attack, it just limits the character to 1 attack regardless of how many attacks they have and the source. This means that the second half of Bladesinger's Extra Attack is still available to use.

DM ruling is required

I think the rules are sufficient to say that the Bladesinger's special unique ability can be used even when hasted. However your DM may say otherwise. The rules are not clear in this case, so it may be a good idea to discuss it with them.

Answer 7

I mostly agree with Tiger Guy's answer, but you could also argue that Haste gives you another "attack action" but only to do 1 weapon attack. Haste says:

That action can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object action.

but due to English wording, adding the last word to each action name, it appears to be saying:

That action can be used only to take the Attack action (one weapon attack only), Dash action, Disengage action, Hide action, or Use an Object action