If a sentient item such as Blackrazor maintains concentration on a spell but does not have a Constitution score, can its concentration be broken?

Question

Some sentient items in D&D have spellcasting capabilities. For example, the description of the sentient magic greatsword Blackrazor says (DMG, p. 217):

Blackrazor can cast the haste spell on you once per day. It decides when to cast the spell and maintains concentration on it so that you don't have to.

However, Blackrazor does not have a Constitution score:

Blackrazor is a sentient chaotic neutral weapon with an Intelligence of 17, a Wisdom of 10, and a Charisma of 19. It has hearing and darkvision out to a range of 120 feet.

If a person is wielding Blackrazor and is under the effect of the haste spell cast by Blackrazor, can that spell's concentration be broken?

Answer 1

RAW (Rules As Written), Sentient Magic Items cannot lose concentration from Constitution Saving Throws

Sentient magic items are often formidable and powerful, and influence the world with wills of their own. However, for the purposes of the rules, there is some strong consensus that sentient Magical items are objects, and not creatures. There is also textual support for this interpretation: the DMG gives guidance for creating a sentient magic item, and states (DMG, p. 216, bold added):

Use the information on creating NPCs in chapter 4 to develop a sentient item's mannerisms, personality, traits, ideals, bonds, and flaws... ignore or adapt any result that doesn't make sense for an inanimate object.

This at least strongly implies that even though they are intelligent and capable of thought (and sometimes action) outside of their user, a sentient magical item is considered an object for the purposes of the rules. As such, they are subject to the rules for objects, including the following from the Player's Handbook (p. 185, bold added)

Objects always fail Strength and Dexterity saving throws, and they are immune to effects that require other saves.

They are subject to the rules on spellcasting in general, so they can lose concentration by dying or becoming incapacitated, having the spell's duration end, or by casting another concentration spell (PHB, p. 203-204). But the most common way of losing concentration for creatures is to fail a Constitution Saving Throw from either taking damage or environmental factors (ibid). And since sentient magical items are "immune to effects that require" Constitution saving throws, they will never lose concentration from (for example) taking damage, unless that damage destroys them or (if such a thing is possible) renders them unconscious.

It's also worth noting that many features of the game that impose the incapacitated status (e.g. the spell Tasha's Hideous Laughter, PHB p. 280) do so by targeting creatures, rather than objects. So sentient magical items are also difficult to incapacitate (or stun, or paralyze, etc.).

A DM could overrule any of these interpretations or rules, of course: they might declare that sentient magic items are creatures at their tables. But it's worth noting that the rules as written leave a lot of how that would work ambiguous (the best example is the one you mentioned: they don't have constitution scores, so how would they roll a Constitution save?). If you go by the rules as they are presented, it seems to me that there are very few things in the game that could cause a sentient magic item to lose concentration, other than killing it or making it concentrate on something else.

Answer 2

I'll begin my answer with a caveat: I'm not sure this scenario will come up too often. With Blackrazor being the item casting the spell, per the rules on concentration, it would need to cast another spell (not applicable here), take damage, or be incapacitated or killed (not applicable either) in order to potentially lose concentration.

As a result, the sword would need to take damage to trigger a Constitution saving throw to maintain concentration. This gets into a larger question on whether a magical item can take damage (somewhat discussed in this answer). Irrespective of how magical items can take damage and how to track that damage, I think we should also keep in mind that it would be fairly unlikely that Blackrazor would take damage (though again, not impossible - for example, the rules on concentration describe a player being hit by a wave, which a DM could rule would in turn cause damage to the weapon and by extension trigger a Con save).

With that in mind...

RAW: unclear. As you've identified, Blackrazor does not have a constitution score, meaning we cannot know what would be rolled assuming a concentration check was necessary. All the description says is that the sword maintains concentration "so that you don't have to." As a result I think we have some interpreting to do.

Possible interpretations:

• Concentration is automatically broken, since the sword does not have a Con score;
• Assigning some Con score commensurate to the damage taken and the specific circumstances of the situation;
• Automatically succeed, since the rules are silent on a Con score, and perhaps since Blackrazor is a legendary weapon (some good info on rarity of magic items in this thread).

At my table: I would probably "rule of cool" the situation. This is a legendary magic item, and it taking damage is such an edge case that I'd probably let the player keep Haste. But I think other DMs could reasonably disagree.