What exactly sets the Unseelie Court apart from the Seelie Court?

Question

I have played fairly little Dungeons and Dragons before the fifth edition, and have some gaps in my knowledge of the lore. One of the bigger holes concerns the nature and differences of the courts of Seelie Fey and Unseelie Fey.

The Dungeon Master's Guide has an info box concerning the courts of Feywild, but it does fairly little to describe the nature of the courts:

Dungeon Master's Guide, page 49 (Seelie and Unseelie Fey)

... Seelie and unseelie do not directly correlate with good and evil, though many mortals make that equation. Many seelie fey are good, and many unseelie are evil, but their opposition to each other stems from their queens' jealous rivalry, not abstract moral concerns.

Rather, it seems to mostly point out that the two courts are not good and evil, but otherwise leaves me guessing about their differences. However, if many mortals do generalize them as such, it hints at the Unseelie indeed being a bit more unscrupulous in at least some ways.

A bit of online searching brought up an old Wizards of the Coast Article, Seelie and Unseelie Courts. Some excerpts on their description of the Unseelie court:

Unlike the selective, restrictive Seelie Court, the Unseelie Court welcomes anyone and everything with even a drop of ancestral fey blood. Fey can and do breed with anything, creating odd, mixed creatures. Most species consider the offspring grotesque monsters. The mutant creatures gravitate towards the Unseelie Court, which welcomes them and gives them an environment where peculiar physiologies and abilities are the norm.

...

After a millennia of indiscriminate breeding, the physical appearance of the Unseelie Court mirrors the macabre. Twisted columns, trees forced into unnatural growth by royal gardeners, are scattered haphazardly through the hall. Curtains of shadows hide blood-soaked alcoves.

However, I find this information, written for earlier editions, to be in direct contradiction with 5e source material:

Dungeon Master's Guide, page 49 (Seelie and Unseelie Fey)

Ugly denizens of Feywild, such as fomorians and hags, are almost never members of either court ...

Volo's Guide to Monsters, page 52 (Hags, Dark Sisterhood)

Because both the Seelie Court and the Unseelie Court appreciate and revere true beauty among the fey, hags are almost never found in either place. The Summer Queen and the Queen of Air and Darkness recognize that hags have valuable knowledge and impressive magic, but they can't abide the stain on the beauty of their surroundings, so most hags are excluded from both courts.

So, clearly Unseelie Fey are no longer supposed to be revelers in the grotesque. What, then, are the differences between the two Fey courts in DnD 5e?

Answer 1

D&D Sources

I think Weckar E. is basically correct in that this confusion stems from the fact that, like many elements of D&D, the fey courts are cobbled together from a mishmash of not-terribly-consistent folklore. There seem to be two competing views:

1. The two courts are basically mirror images of each other - the Seelie project an image of light and the Unseelie one of darkness, but under the surface they are pretty similar, with members of both courts being fickle and beauty-obsessed.
2. A view with more overtones of class warfare, where the Seelie are beautiful and exclusionary while the Unseelie are nightmarish and inclusive.

It sounds like more sources tend toward the first view, but I think there's enough material provided for you to choose whichever one you feel is right for your game.

Other Sources

Other depictions of the two courts that I'm familiar with tend more toward the first view. Often fey from both courts are equally dangerous in their own ways - they merely express their unpredictable personalities and the power of nature differently.

The Dresden Files novels, for example, play up the Summer and Winter connections. The Seelie are bright, colorful, and generally pleasant enough on the surface, but they can also be quick to anger and terrible in their power, like a summer's day giving way to a powerful thunderstorm. Alternatively, they might simply get carried away or be otherwise heedless of the consequences of their actions, turning from pleasant warmth to a dangerous heat wave.

The Unseelie are cold and vicious, but aren't entirely without compassion. After all, winter still has its mild days; it is not an unrelenting blizzard. They still experience some form of love, or at least emotional attachment, and while they might see mortals as playthings most of the time, they may develop a certain admiration for mortals who prove themselves capable of keeping up. Even then, mortals must remain on their guard - it's not uncommon for the Unseelie to have a sadomasochistic streak, and their version of kindness might not seem so pleasant to others.

Answer 2

I think the reason 5e fails to provide adequate information is because these concepts stem heavily from real life folklore:

The categorization of fairies based on court is whether or not a fairy is light or dark. The Seelie court are known to seek help from humans, to warn those who have accidentally offended them, and to return human kindness with favors of their own. Still, a fairy belonging to this court will avenge insults and could be prone to mischief. The most common time of day to see them is twilight. Other names for the Seelie court are 'The Shining Throne' or 'The Golden Ones' and 'The Summer Court'. Seelies are known for playing pranks on humans and having a light hearted attitude, forgetting their sorrows quickly and not realizing how they might be affecting the humans they play pranks on.

The Unseelie Court consists of the darkly-inclined fairies. Unlike the Seelie Court, no offense is necessary to bring down their assaults. As a group (or "host"), they appear at night and assault travelers, often carrying them through the air, beating them, and forcing them to commit such acts as shooting at cattle. Like the beings of the Seelie Court who are not always benevolent, neither are the fairies of the Unseelie Court always malevolent. Most Unseelies can become fond of a particular human if they are viewed as respectful, and would choose to make them something of a pet.

~ Wikipedia: "Classifications of fairies" [4-5-2017/12:17]

Answer 3

The problem with 5th edition's fey lore is that it's trying to make homages to 4th edition's fey lore, which was the most developed fey lore that we've ever had in D&D, whilst simultaneously denying it exists by trying to focus on the older, more basic lore, which was a more direct porting of real-world Seelie and Unseelie lore from Celtic mythology. Not helping is that older D&D lore is little-detailed, widely scattered, and not organized.

In AD&D, the Seelie and Unseelie were, as I said, more or less direct ports of Celtic lore, without much context or emphasis placed on them. The Seelie Court were essentially the "Good Fey", and inhabited a demiplane that roamed across the Neutral Good to Chaotic Good Outer Planes. The Unseelie Court were the "Evil Fey", and just sort of existed.

In 3e, there are two different presentations of the Seelie and Unseelie. The first version, the one from the books, is essentially a continuation of the AD&D version; two warring Chaotic Neutral factions with strong Chaotic Good or Chaotic Evil tendencies (Seelie vs. Unseelie) - this is emphasized by the Plane of Faerie in the 3rd edition Manual of the Planes describing the Seelie as "Half-Celestial Fey" and Unseelie as "Half-Fiend Fey". The second version, the one you cite from Wizard's archive page, was invented for the website and has no precedent or presence in the game material of the time.

In 4th edition, the Fey as a whole are organized into the Court of Stars, which is made up of many different factions. The Summer Fey, who are fey centered around concepts such as growth, life and good fortune, are the closest to the Seelie Court of old, and generally have a positive attitude towards mortals. The Unseelie Court of old is divided into two factions; the Winter Fey (associated with ice, darkness, death and ill fortune, largely hostile towards mortals) and the Unseelie Fey (fey who have ties to the Shadowfell, corrupted by shadow magic). However, in 4e, the terms "Seelie" and "Unseelie" are mortal inventions ("seelie" means "will respect mortals who try to respect and adhere to fey customs", "unseelie" means basically the opposite), and they do not apply to any faction as a whole - you can find Seelie formorians and hags as well as Unseelie eladrin, nymphs and dryads.

5th edition has basically gone back to the AD&D/3e definition of the term.