[RPG] difference between “When you are reduced to 0 hit points” and “when you would be reduced to 0 hit points”

dnd-5ehit-points

There already exist a few questions asking similar things about such scenarios, like the following:

What I am wondering is whether the wording differences between all of the following features means anything; how should these wording differences be interpreted/used? In particular, some features use the phrase "when you would be reduced to 0 hit points" while others use the phrase "when you are reduced to 0 hit points".

The first link above currently has an answer stating that the wording difference is important, and that it does result in differences between the features and rulings regarding them. Below are some example features:

Barbarian's Relentless Rage feature:

If you drop to 0 hit points while you're raging and don't die outright, you can make a DC 10 Constitution saving throw. If you succeed, you drop to 1 hit point instead.

Undead Fortitude feature (Zombie):

If damage reduces the creature to 0 hit points, it must make a Constitution saving throw […] On a success, the creature drops to 1 hit point instead.

Half-Orc's Relentless Endurance feature:

When you are reduced to 0 hit points but not killed outright, you can drop to 1 instead.

Druid's Wild Shape feature:

You automatically revert if you fall unconscious, drop to 0 hit points, or die.

Long Death Monk's Mastery of Death feature:

When you are reduced to 0 hit points, you can expend 1 ki point (no action required) to have 1 hit point instead.

Relentless Feature (Boar):

If the boar takes 7 damage or less that would reduce it to 0 hit points, it is reduced to 1 hit point instead.

Death ward spell:

The first time the target would drop to 0 hit points as a result of taking damage, the target instead drops to 1 hit point, and the spell ends.

Only the last two features actually use the phrasing "would drop" and "would reduce" instead of simply "are dropped" and "are reduced" (or similar). Does this mean that death ward and the Relentless feature act differently in terms of rulings to be made?

Is there a difference between "when you are reduced to 0 hit points" and "when you would be reduced to 0 hit points?"

I would like answers to assume that the wording choice of "if" vs "when" is irrelevant. These words (at least to me) seem to be used interchangeably throughout the rules with no difference in meaning, so they can be ignored here. Alternatively, if you feel they are different, that should be a separate question of its own.

Best Answer

Grammatically speaking, there is a very important difference, and that is order of operations.

When you are reduced/drop to 0 hitpoints

The order of operations is as follows:

  1. You take damage
  2. You have 0 hit points
  3. The feature that activates when you are reduced to 0 HP kicks in
  4. You have 1 HP instead

When you would be reduced/drop to 0 hitpoints

The order of operations is as follows

  1. You take damage
  2. The damage would have reduced you to 0 hp
  3. You have 1 HP instead

Thus, the big difference here is that features that activate when you are reduced to 0 hitpoints mean you still had 0 hitpoints for a moment. On the other hand, features that activate when you would be reduced to 0 hitpoints activate before you hit 0 HP, so you never had 0 HP.

This is important for effects that immediately kill you if you hit 0 hitpoints. There is a slightly out-of-date sage advice comment to this effect:

If the damage from disintegrate reduces a half-orc to 0 hit points, can Relentless Endurance prevent the orc from turning to ash? If disintegrate reduces you to 0 hit points, you’re killed outright, as you turn to dust. If you’re a half-orc, Relentless Endurance can’t save you.

I will note (as an aside) that since this Sage Advice item was created, errata has altered the Disintegrate spell--which likely changes the outcome laid out for that specific spell. (That bit of Sage Advice is from 2016, the errata is 2018)

The target is disintegrated if this damage leaves it with 0 hit points.

Based off of this change in wording, effects that activate when you are reduced to 0 HP would still save you from Disintegrate because you are not left with 0 hit points. On the other hand, a Beholder's Death Ray...

The target dies if the ray reduces it to 0 hit points.

In this case, an effect that activates when you are reduced to 0 HP would not save you--because you were reduced to 0 HP before that feature activated, and thus died before the effect could activate. However, an effect that activates when you would be reduced to 0 HP can save you--because you were never actually reduced to 0 hp.

As a bit of non-official support, here's a comment from J. Crawford on Twitter...

Q: does death ward prevent disintegration?

A: Death ward works against any effect that would reduce you to 0 hp via damage or that would kill you instantly without dealing damage.

While Crawford's tweets are no longer considered official, it does offer perspective. Back when Disintegrate could kill you through Polymorph or Relentless Endurance, Death Ward could protect you from those before you never actually reached 0HP.

Order of Precedence

This is a bit of odd English to try to explain, but I'll do my best. The sequence in which the four terms used here would happen in goes like this:

  1. Would Be: This is future-facing and happens first, in anticipation of the event
  2. Reduces: Active Event, this occurs simultaneous to the triggering event
  3. Are Reduced: Reacts to the event, this occurs after the reduction has happened
  4. Leaves it with: Final state, occurs once all 'events' have ceased.

TL;DR:

A Half-Orc's Relentless Endurance would not save you from death via being reduced to 0 HP by a Beholder's Death Ray--while the spell Death Ward would. This is because Relentless Endurance activates after you have been reduced to 0 HP, while Death Ward happens before you would be reduced to 0 hp.

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