Casting a Somatic, non-Material spell while holding a focus

Question

In this question a side issue came up of whether you can cast a spell with Somatic components but no Material components while holding a focus in the hand used for Somatic components.

My reading of the rules sees "A spellcaster must have a hand free to access a spell's material components--or to hold a spellcasting focus--but it can be the same hand that he or she uses to perform somatic components." - it doesn't say you have to be holding the focus for the purpose of avoiding materials.

However, @Adeptus and @enkryptor argue that - since that rule is in the section on Material components - you don't consult it in for spells without Material, and fall back to the Somatic rule "the caster must have free use of at least one hand".

(I also appeal to the logic of fluff - why should it be harder to cast a spell with fewer components?)

Is there an official RAW or Word Of God on this matter? Can you cast a material-less, somatic spell while holding a focus in your only free hand?

Answer 1

You will need the free use of a hand without the focus

This was elaborated on in the Rules of spellcasting sage advice column.

Another example: a cleric’s holy symbol is emblazoned on her shield. She likes to wade into melee combat with a mace in one hand and a shield in the other. She uses the holy symbol as her spellcasting focus, so she needs to have the shield in hand when she casts a cleric spell that has a material component. If the spell, such as aid, also has a somatic component, she can perform that component with the shield hand and keep holding the mace in the other.

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 we extrapolate the above example to include any spellcasting focus, which we are allowed to do since there is no mention anywhere of a holy symbol being an exception to any general somatic component rule, then any spell with a somatic component and no material component requires a hand that isn't holding anything.

Why should a spell with fewer components be harder to cast?

The in-universe reason why you can't use the focus for non-material spells is, in some way, setting dependent. A DM is well within their purview to ignore this rule entirely, or justify it in whatever way they see fit. One way that you might justify this rule, and the way I do it in my own games, is by saying that material components focus the magical energies used to create the spell to some extent that it makes it easier to cast the somatic components. Basically, because of the extra focusing power of the material components, your gestures don't need to be as exact to get the job done and cast the spell.

Without material components, your somatic (and potentially verbal) components don't get that extra boost, so they need to be absolutely precise for the spell to cast properly. As a result, without special training à la Warcaster feat, your hands need to be completely free to assure a proper cast.

Answer 2

This is clearly not the intention. Sage advice should make an errata on this ruling. There are multiple examples of bonus action, somatic, non-material spells that are intended to be coupled with an attack.

Divine Favor:

Your prayer empowers you with divine radiance. Until the spell ends, your weapon attacks deal an extra 1d4 radiant damage on a hit.

This is intended to empower weapon attacks with extra radiant damage.

Here's the scene: your paladin is in battle sword and shield whirling. He wishes to call on his god's divine favor. He raises his sword high and calls out to Helm for power. Helm ignores his call, he would rather his champion put his sword away and strike unarmed while imbued with bonus damage on weapon attacks.

No, this is obviously not the intention of this spell and others like it.

I think the intention in the Sage Advice post was this: that when casting a spell like Cure Wounds, you touch the wounds that are being knitted together, and you'd not be bashing your ally with your shield to heal them. This doesn't hold water when applied more broadly.

You can certainly cast magic missile instead of lightning bolt while holding a staff and orb as in the linked example.