Can the Contingency spell be used with a spell cast from an Ioun Stone?

Question

Contingency says:

Choose a spell of 5th level or lower that you can cast, that has a casting time of 1 action, and that can target you. You cast that spell--called the contingent spell--as part of casting contingency, expending spell slots for both, but the contingent spell does not come into effect.

Would one be able to use a spell that is cast from a Reserve Ioun Stone as the contingent spell?

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For example: A bard casts revivify into the Reserve Ioun Stone and gives it to the wizard who then uses contingency along with the stored revivify to create an effect that would revive him upon falling unconscious. The wizard cannot cast revivify normally.

Would this work?

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My specific concerns are:

1. Does having the spell stored in such a way count as a spell "you can cast"?
2. Does the fact that the spell is stored in an item mean that it can't be cast as part of another spell as contingency requires?
3. Is there any other reason why this would not work?

Answer 1

Stone Casting Likely Allowed, but there is case for No.

The Reserve Ioun Stone only states that:

While this stone orbits your head, you can cast any spell stored in it.

There is no difference in casting language between the stone or a spell naturally, just that you can cast any spell stored in it.

However, there is a case against this with the requirement of expending a spell slot (see below.)

If allowed, this is an excellent way to expand the list of possible Contingent spells outside of the traditional Wizard spell list.

Next is to look at the requirements of Contingency

Choose a spell of 5th level or lower that you can cast, that has a casting time of 1 action, and that can target you. You cast that spell—called the contingent spell—as part of casting contingency, expending spell slots for both, but the contingent spell doesn’t come into effect.

What happens here is that you have cast both Contingency as well as the spell from the Ioun Stone (assuming it passes the criteria of 1 action casting time and targets only yourself).

Do note that this frees up the space in the Ioun Stone as the spell has been cast.

The spell cast from the stone is no longer stored in it, freeing up space.

The contingent spell is fully cast and just waiting to come into effect. There is nothing more needed for the spell to take effect other than the trigger provided.

To answer your specific questions:

1. Does having the spell stored in such a way count as a spell "you can cast"?

   Yes, the language is identical between casting from an ioun stone or casting naturally.

2. Does the fact that the spell is stored in an item mean that it can't be cast as part of another spell as Contingency requires?

   There is nothing to suggest this given the casting language is identical.

3. Is there any other reason why this would not work?

   The main remaining concern is the requirement from Contingency of

   expending spell slots for both [Contingency and the spell to be triggered].

   If it is required for a spell slot to be used, then using the Reserved Ioun Stone will not qualify as there is no spell slot expended.

   I think this is a bit of a stretch, but a strict RAW reading may preclude the use of the Stone with Contingency because it failed to expend the spell slot.

   This concern is similar to Ring of Spell storing requiring a spell slot to be expended when casting a spell into it. Jeremy Crawford confirms that here

   It requires a spell slot. A wand doesn't expend a spell slot.

Comparison to other Items:

Ring of Spell Storing

The Ring of Spell Storing also uses similar language and should be able to be used in this way as well.

While wearing this ring, you can cast any spell stored in it.

Hat of Disguise

This is an example of something that would not work with contingency. The language here requires an action to cast Hat of Disguise.

While wearing this hat, you can use an action to cast the disguise self spell from it at will.

Answer 2

Technically yes.

This is gonna be one of the really hair splitting questions, isn't it?

Well the wording of Ioun stone does say

While this stone orbits your head, you can cast any spell stored in it. The spell uses the slot level, spell save DC, spell attack bonus, and spellcasting ability of the original caster, but is otherwise treated as if you cast the spell. The spell cast from the stone is no longer stored in it, freeing up space.

so technically you can cast the spell and there are no issues with it.

The issues

There are two things to worry about with this.

1. The issue of using material components is not resolved in the stone's description so you might or might not need material components for the stored spell that might be "exotic" to your class.

2. GM might just not allow this narratively, since it might seem against the intended use (to me it does) as you are using someone else's spell that you cannot normally cast.