Sanctuary + readied spell that affects an enemy

Question

If I am under Sanctuary and ready an action to cast a spell such as Shocking Grasp, what actually happens? Sanctuary says:

If the warded creature makes an attack, casts a spell that affects an enemy, or deals damage to another creature, this spell ends

Readying a spell says:

When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs. To be readied, a spell must have a casting time of 1 action, and holding onto the spell's magic requires concentration. If your concentration is broken, the spell dissipates without taking effect. For example, if you are concentrating on the web spell and ready magic missile, your web spell ends, and if you take damage before you release magic missile with your reaction, your concentration might be broken.

So since I'm holding the energy of the Shocking Grasp, I believe the spell does not affect its target before its released. Would I be protected by Sanctuary until the readied action takes place? It seems that way to me, but then again the spell is cast and does affect an enemy...it just hasn't affected the enemy yet. I guess it comes down to parsing "a spell that affects an enemy"; does this mean "a spell that, at some point, affects an enemy" or "a spell that affects an enemy in this instance"?

Answer 1

You would be protected

For the second condition

casts a spell that affects an enemy

two things need to happen for your protection to lapse: (1) you cast a spell, (2) it affects an enemy. You could for example also cast Edward's Black Tentacles on an area, and the Sanctuary will not end until an enemy gets caught in the effect or someone takes damage from it.

The idea is that Sanctuary shields you as long as you take no directly aggressive actions, and that is technically expressed in the listed conditions. You can see this in the pedigree of the spell, which goes back all the way to first edition (even if it technically does not matter for fifth edition):

During the period of protection afforded by this spell, the cleric cannot take offensive action, but he or she may use non-attack spells or otherwise act in any way which does not violate the prohibition against offensive action.

Answer 2

It does not say “a spell that can affect an enemy”.

For it to be said that I have “cast a spell that affects an enemy”, I have to actually affect an enemy. If I have affected no enemies, I have not cast a spell that affects an enemy. This would be different if sanctuary said “casts a spell that can affect an enemy”. But it doesn’t say that.

Answer 3

By comparing to a similar case, sanctuary ends when the spell is cast

The following question already exists:

• When must the wizard choose to overchannel?

Comparing the wording of Overchannel and sanctuary then:

If the warded creature [...] casts a spell that affects an enemy

When you cast a wizard spell [...] that deals damage

All three positively-scoring answers there state that Overchannel is decided when the past is cast and not when it deals damage. To quote the highest-scoring one:

If it was meant to be decided after it had dealt damage, it would have to use wording like "When you cast a wizard spell of 5th level or lower and deal damage".

I believe the exact same case can then be made for sanctuary. Whether or not sanctuary ends is determined when you cast the spell and thus we must decide whether the spell affects a creature at the moment it is cast. Just like with Overchanneling, this would be determined based on whether or not we expect the spell to affect a creature, given its description. The shocking grasp spell certainly expects a target, so I would rule that sanctuary ends the moment you ready it.

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Other similar cases:

• Does Elemental Affinity add damage to Witch Bolt only once?
• Does the Draconic Bloodline sorcerer's Elemental Affinity feature apply to the spell Dragon's Breath?
• Is Heart of the Storm triggered by spells that may or may not deal lightning or thunder damage?