Does an unconscious creature still use its dexterity to avoid attacks?

Question

Related - How does one dispatch a helpless opponent?

Here's the unconscious condition description:

Unconscious

An unconscious creature is Incapacitated, can't move or speak, and is unaware of its surroundings The creature drops whatever it's holding and falls Prone. The creature automatically fails Strength and Dexterity saving throws. Attack rolls against the creature have advantage. Any attack that hits the creature is a critical hit if the attacker is within 5 feet of the creature.

So attacks against the creature have advantage, and any attack that hits is a critical - but you still can miss because of the creature's AC. Armor Class includes dexterity bonus. The description doesn't say the creature's AC changes somehow.

Does it mean the creature still benefits from its dexterity, both in terms of mechanics and in-game world?

An example situation

A low-level party of Barbarian and Bard fights a sneaky thief, who has AC of 15 due to his +4 dexterity bonus. The Barbarian attacks, so does the Bard, but their results are 12 and 13. DM described that the thief was twisty enough to dodge both attacks.

Next round, the Bard puts the thief to sleep (hence, unconscious) with the Sleep spell. The barbarian makes a melee attack with advantage, but his best result is 14. It is still a miss, isn't it? As a DM, how can I plausibly describe such an outcome?

Answer 1

The gist: your Armor Class remains the same despite being unconscious. You can justify a miss by saying the unconscious target was not hurt by the attacker's careless attack.

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Yes, your AC is still kept the same

Your thief's AC is 15, before and after succumbing to the sleep spell. That is simply how AC is calculated (Base AC of Armor + Dex mod), as written in PHB 144.

PHB 144

Armor Class (AC). Armor protects its wearer from attacks. The armor (and shield) you wear determines your base Armor Class.

Followed by the AC specified in PHB 145 on how to calculate Armor Class from Padded or Leather armor: \$11 + \text{Dex modifier}\$

How is this narratively justified?

Armor Class is not how hard you are to hit, but how hard you are to wound.

Armor Class, PHB 14

Your Armor Class (AC) represents how well your character avoids being wounded in battle.

The difference is usually immaterial, but in this case, it is important. The Barbarian could still have hit the Thief, they just failed to hurt them.

We can also take guidance from how Armor Class is calculated for objects:

Statistics for Objects, DMG 246

Armor Class. An object's Armor Class is a measure of how difficult it is to deal damage to the object when striking it (because the object has no chance of dodging out of the way).

Objects cannot dodge, much like a sleeping creature, so you instead use AC to represent how hard it is to damage the object. Interestingly, the following ACs are used for the brittle materials:

\begin{array}{|c|c|} \hline \textbf{Substance} & \textbf{AC} \\ \hline \text{Cloth, paper, rope} & 11\\ \hline \text{Crystal, glass, ice} & 13\\ \hline \text{Wood, bone} & 15\\ \hline \end{array}

Your unconscious Thief, as it turns out, has the same AC as bone. This means, even after being hit by something (because it can't dodge), bone is still difficult to damage. It is probably resilient enough that you cannot crack or snap it in one blow.

In other words: you can let your Barbarian's swing hit the Thief, but you can justify by saying, despite the impact, did not actually hurt the target. They could bruise, or get a cut, or a small puncture wound, but the nature of the blow is such that the target was not meaningfully harmed.

Also narrate the failure of the Barbarian

Despite having Advantage, your Barbarian's best roll was still a 14. That is a failure on their end, not just a product of the resilience of your unconscious Thief. Focus on that as well.

You can say that the Barbarian thought they were aiming for the head, but they lost their footing slightly during the swing, or aimed too quickly or too excitedly, or the hilt on their weapon slacked just a bit. You can also add an external factor to the blow, and use that external factor to explain why they failed to deal damage.

Answer 2

YES, AC is calculated as normal

The game effects listed under the Conditions state the effects. You can add more to your table, but the RAW is that AC remains the same.

Increased chance to hit accounted for by Advantage?

However, you can read that the Advantage granted to attacks within 5' accounts for this as it basically is a positive modifier to the roll and gives the additional critical hit for any hit.

5e has simplified a lot of the mechanics with Advantage/Disadvantage as it accounts for a positive/negative modifier into the roll. By allowing advantage, it is accounting for the it being easier to hit the target.

Roll Mechanics for Advantage/Disdadvantage

This question on passive perception covers a possible explanation of the mechanical result of advantage/disadvantage for passive rolls by utilizing a +5/-5 modifier. This gives some indication as to the meaning and power of Advantage/Disadvantage when applying to other d20 rolls.

Answer 3

Up to the DM, but RAW no

Does it mean the creature still benefits from its dexterity, both in terms of mechanics and in-game world?

An unconscious creature does not use its dexterity narratively, but in terms of mechanics its AC does not change. This discrepancy was explicitly taken into account in previous versions. For instance, 3.x version had three different ACs — "normal", "flat footed" (no dodge) and "touch" (no armor). As a result, a DM had to recalculate AC on the fly for multiple creatures, especially when spells (like sleep) affected them, which could waste a lot of players' time.

The 5th edition moved away from such a paradigm, leaving these minor adjustments up to the DM's rulings. Moreover, there is an official adventure module Dues for the Dead which actually suggest doing exactly that, see page 17:

Because he is unconscious, he loses his Dexterity modifier to AC

So it's completely valid ruling, however, base sourcebooks does not have an explicit rule for that anymore.

Answer 4

Narratively, it does not make sense. In terms of game mechanics, however, 5e decided to use one simple AC for any given creature, and leave it at that to make the game flow better and be easier to play. With the original AD&D 1e, every character had several different AC ratings, depending on facing, use of dexterity, shield use, and several other possible factors. I had characters with as many as 8 different AC ratings, depending. 5e cut that back to two possibilities -- (1) choose how to calculate your AC, (2) pick up or put down your shield. That's it.

As a DM, you are of course free to add various factors back in, and make the game more complicated, but I think that's not in the spirit of the current game design. Yes, with regard to AC, and falling, and unarmed attacks, and a few other bits, this means you must squint a bit, look sidelong, and either (a) accept that the system does not replicate reality well, or (b) modify the rules for whatever aspect is bugging you.