Can I use a hand holding a focus from one class to cover somatic components for a spell from another class?

Question

I want to try playing a multiclass Hexblade 2 / College of Swords Bard 18, but I'm concerned about how focused will work.

I intend to hold a shield in one hand with a sword in the other. Thanks to College of Swords I am able to use the sword as a focus for my bard spells. However, I was hoping that I would be able to cast Shield from my hexblade spell list in the thick of battle.

As Shield requires a Somatic component, would I be able to use my sword hand (which is holding a focus, but for bard spells not warlock spells) to cover the Somatic components of Shield? I know that if it had a Material component I would need an arcane focus, but this situation seems ambiguous to me.

tl;dr Can I use my hand holding a bardic focus to cover the Somatic components for a Warlock spell?

pg. 15 XGtE under Bonus Proficiencies:

If you're proficient with a simple or martial melee weapon, you can use it as a spellcasting focus for your bard spells.

pg. 203 PHB under Material (M):

A spellcaster must have a hand free to access these components, but it can be the same hand that he or she uses to perform somatic components.

This doesn't actually state that materials are required for you to use the a hand holding the material components to perform somatic components.

I was really just hoping to get a response that cited a rule I might have missed (preferably about multiclassing, but such rules in the PHB skip over foci entirely).

Answer 1

No, you must have a free hand for Somatic Components

From RAW, you actually can't use the hand holding a focus as a Somatic component if it does not have the Material component as well, even for your own spells, so you can't use it for another class' spells either.

From PHB

Somatic. Spellcasting gestures might include a forceful gesticulation or an intricate set of gestures. If a spell requires a somatic component, the caster must have free use of at least one hand to perform these gestures.

Note that it does not say "free hand or spellcasting focus".

The exception is made for when there is a Material component involved as well

A spellcaster must have a hand free to access these components, but it can be the same hand that he or she uses to perform somatic components.

If it also has the Material tag

Then it is ambiguous if the Spellcasting focus can be used as the same hand as the Somatic component. The spellcasting focus can not be used as the Material component, though, as your quoted text indicates:

If you're proficient with a simple or martial melee weapon, you can use it as a spellcasting focus for your bard spells.

So it doesn't matter.

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If you need further clarification, the lead design, Jeremy Crawford, states in his twitter, which is considered official ruling by WotC. Note: This (tweets being considered official rulings) is no longer true, but I will let it stay for historical reasons.

I'd say yes if the holy symbol is being used as the material component of the spell, so yes if "S, M," but no if only "S."

The question is about the Holy Symbol for Cleric, which is the same as any other Spellcasting focus.

This was later included in the Sage Advice Compendium:

If the same cleric casts cure wounds, she needs to put the mace or the shield away, because that spell doesn’t have a material component but does have a somatic component. She’s going to need a free hand to make the spell’s gestures. If she had the War Caster feat, she could ignore this restriction.

Note that the Cleric with a shield is used as an example for the general rule (i.e., it is not an exception). Being a Shield has nothing to do with the clarification, the reasoning is clear: "because that spell doesn’t have a material component but does have a somatic component.". Nowhere is states anything about "because the shield is more restrictive" or "if it was an Arcane Focus, this would change." The shield is treated as a Spellcasting focus as any other by the rules.

Answer 2

No, the sword only works for Bard spells. You’ve quoted the necessary rule already:

If you're proficient with a simple or martial melee weapon, you can use it as a spellcasting focus for your bard spells.

For non-bard spells, you can’t use the sword as a focus unless that class says so, which none do.

Generally, foci are defined by a class, and then limited to that class’s spells. All spellcasting classes say what kind of focus can be used for that class’s spells. For all other classes, it simply doesn’t count as a focus, because the other class doesn’t list it as a permitted focus for its spells.

For example, the warlock class specific an arcane focus can be used for warlock spells:

You can use an arcane focus as a Spellcasting focus for your warlock spells.

What counts as an arcane focus is covered in the Equipment chapter (PHB, Basic Rules, or SRD):

Arcane Focus: An arcane focus is a Special item— an orb, a Crystal, a rod, a specially constructed staff, a wand-like length of wood, or some similar item— designed to channel the power of arcane Spells. A Sorcerer, Warlock, or Wizard can use such an item as a Spellcasting focus.

A sword doesn’t qualify as an arcane focus, so it can’t be used for warlock spells.