Is using a shield "wearing armor" or not? Conflicting rulings on Defense Fighting Style and Shield Proficiency

Question

The "Armor Proficiency" part of the Armor section on the PHB reads:

Anyone can put on a suit of armor or strap a shield to an arm. Only those proficient in the armor’s use know how to wear it effectively, however. Your class gives you proficiency with certain types of armor. If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can’t cast spells.

The implication here being that using a shield is "wearing armor", otherwise there would be no downside to using a shield without proficiency, making shield proficiency completely useless.

The Defense fighting style reads:

While you are wearing armor, you gain a +1 bonus to AC.

So my understanding would be that using a shield counts as wearing armor, and thus enables someone to take advantage of the defense fighting style, however when I look at questions like this one it seems widely accepted that shields don't count as "wearing armor".

Am I missing something or are these rulings completely contradicting each other?

I would lean towards shield usage to be counted as "wearing armor", the idea that shield proficiency is completely useless seems less logical than allowing a Barbarian or a Monk access to the Defense fighting style. Has this inconsistency been addressed officially?

(I'm aware there is already questions addressing either of these rules separately, but this is not a duplicate of those, I'm specifically asking about the contradiction created by these two rules existing together.)

Answer 1

Language use in the rules is inconsistent, so you need to look at context of the rule or feature in question

The language use in the core rules is not fully consistent (and this is an issue that has plagued earlier editions, too).

Contradictory uses of the term "armor"

For example, shields are listed in the "Armor" table, not the "Armor and Shields" table on p. 145, but the section in the rules is called "Armor and Shields". Moreover, the text introducing the table also mentions that "Many warriors supplement their armor with a shield", and if you supplement armor with a shield, the shield is something else but armor.

As another example, in class descriptions, shield proficiency is listed in the "armor" line of the Proficiencies section, along with armor proficiency, not in the "armor and shields" line. But there is a separate shield proficiency, in addition to light, medium and heavy armor proficiency. Does this, like the inclusion of shields in the armor table, suffice to say shields are a type of armor?

Third, and most starkly, certain class features refer to being armored and mean different things by it. Both the Monk and the Barbarian have a feature called Unarmored Defense. The monk's feature says "while you are wearing no armor and not wielding a shield", so here unarmored means without armor and shield, making someone with a shield armored; in contrast, the barbarian's says "While you are not wearing any armor", not mentioning shields, so here unarmored means only without body armor, making someone with a shield not armored.

Most of the time, armor just means armor, not shields, but to really understand if "armor" in a passage refers to just bona fide armor like plate armor, or is used in a wider sense, meaning "armor and shields", you need to look at the context in which the word is used.

Armor proficiency

In particular, one of the main sources of confusion is a passage titled Armor Proficiency (p. 144 PHB) that seems to indicate that either the term "armor" must include wearing shields, or wearing a shield without proficiency does not cause disadvantage, because the sentence about disadvantage only mentions armor, not shields:

Armor Proficiency. Anyone can put on a suit of armor or strap a shield to an arm. Only those proficient in the armor’s use know how to wear it effectively, however. If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can't cast spells. [emphasis added]

When the sentence that talks about disadvantage and only mentions armor and omits shields, does it mean only armor proper, or does it mean armor in the sense of "armor and shields"? Following our observations above, to resolve this we can look at the context, both direct and in other parts of the rules.

1. Direct Context: The first sentence in the paragraph talks about both armor or shields, it mentions "or strap a shield to an arm", setting context that this paragraph is about both armor and shields. Otherwise, the mentioning of shields would make no sense -- they do not show up later in the paragraph again.

2. Other Rules Context: The PHB says on p. 14: "There are drawbacks to wearing armor or carrying a shield if you lack the required proficiency, as explained in chapter 5." This again makes a difference between wearing armor and carrying a shield. But if only armor proper and not shields caused the drawbacks, carrying a shield without proficiency would not have a drawback, and this is in direct contradiction to this rule text.

From these it is clear that for the Armor proficiency section "armor" must mean "armor including shields" when it talks about the effect, and that is what the spellcasting rules refer to, too, when they talk about being unable to cast in armor.

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Note: big sections of this are lifted from the answer here, which covers much of the same ground, but in response to a question with a slightly different context.

Answer 2

Wielding a shield is not wearing armor

A thorough reading of the text in Player's Handbook and subsequent Sage Advice questions lead me to believe that wielding a shield indeed does not count as wearing armor.

Let's go over some of the text in chapter 5 of Player's Handbook. While the shield entry indeed does appear on the Armor table, the text has the following to say about it:

The Armor table collects the most commonly available types of armor found in the game and separates them into three categories: light armor, medium armor, and heavy armor. -- The Armor table shows the cost, weight, and other properties of the common types of armor and shields used in the worlds of D&D.

The table itself has four categories instead of the three mentioned, with the shield being its own category. This, and the above text making two separate attempts to draw distinction between armor and shield suggest they are two different things despite being lumped onto one single table.

We can find further evidence for this point by examining the spell Mage Armor and the Sage Advice about it. The relevant part of the spell states:

You touch a willing creature who isn't wearing armor --

And Sage Advice further elaborates on this point:

Can you use a shield with mage armor? Mage armor works with a shield. Shields are grouped with armor in the equipment rules in the Player’s Handbook, but various game features distinguish between the armor you wear and a shield you wield. Take a look at the monk’s Unarmored Defense feature and compare it to the barbarian’s version. In the monk’s version, you must both forgo wearing armor and forgo wielding a shield if you want to benefit from the feature, whereas a barbarian must only forgo wearing armor.

This goes to show that there is a deliberate distinction between wearing armor and wielding a shield. The spell has recieved no errata despite being a subject of Sage Advice suggesting that the wording is deliberate and considered sufficient to be understood as not forbidding the use of shields in conjunction with the spell. The mentioned barbarian Unarmored Defense feature does explicitly spell out you can use a shield, but it didn't have to: Saying "not wearing armor" would have had the same effect on its own and the mention of shields is simply a friendly extra reminder.

But what about shield proficiency?

The above answer does leave the use of shield proficiency in a slightly ambigous light. The armor proficiency text does open up by mentioning both armor and shields (and remember, there is no "flavor text" in 5e), but the actual sentence directly stating the rule and its effects fails to mention shields:

If you wear armor that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can't cast spells.

Thus, a strict RAW reading would render shield proficiency pointless given that there's no penalty mentioned to using one without it. This does seem nonsensical and were I tasked to try and divine the developer intention behind these rules I'd imagine they simply forgot they should've mentioned shields separately. I'd take it the Armor Proficiency rule was meant to read something like this for the intended effect:

If you wear armor or wield a shield that you lack proficiency with, you have disadvantage on any ability check, saving throw, or attack roll that involves Strength or Dexterity, and you can't cast spells.

Alas, this text hasn't received any errata either and I'm not aware of any official statements made about it.

Footnote: Some further confusion in Sage Advice

Skimming through the Sage Advice compendium one can also find the following curious remark on wielding shields:

Can the Disarming Attack maneuver disarm a creature of a shield it has donned? No. Disarming Attack forces a creature to drop an object it is holding. Donned shields aren’t merely held.

So, we can take it shields are not armor you wear, yet they are something you don as per the armor donning rules. They are clearly something less than worn armor but something more than a held item, but the rules do not elaborate on this further.