Everybody has a Ghost
Everybody has a Ghost who sings like you do
Yours is not like mine
But it's alright, keep it up

Ghost - Live

Creation Songs
What makes a ghost? There are as many answers as there are ghosts to testify to them.
For some it is a case of unrequited love that has never been resolved, and cannot be put away. For others, a horrible accident or vicious murder cries out for redress, or recognition. Some fall prey to terrifying madness, however silent or obvious, while others succumb to old age, or sickness, or a strange, fatal irony. Even those who die in peace in their sleep might have cause to come back, for one reason or another.
There is no true formula to predict what lets one soul go on and holds another back - no exact science of the soul. Some say it's choice, some say it's chance, and some say it's a cosmic conspiracy. Still others say it's all a matter of Fate, which lies somewhere between those three boundaries.
Whatever the reason, there are times that the soul does not depart from the world the way that it should. The most precious and painful things left behind, and the feelings they engender, deny these souls full flight from their mortal coil. These great and weighty things are known as Anchors, and they hold the soul down as surely as any chain, prohibiting the peace their final journey into death should bring.
What is left behind, fettered to these Anchors, is a spectral mockery of what once had flesh, a voice and a will of its own. It is a shadowy echo of what was mortal: a stillborn voice, whispering in the darkness, and begging - however unconsciously - for the attention of the living.
A ghost, for want of a better word.

Sleeping Reason

Drifter - Sleepwalk
Drifter - Sleeptalk
Awake to who is following
- Siouxsie and the Banshees

Ghosts are drowsy, stunted things, endlessly repeating key moments of their lives over and over again. Wraiths call them Sleepers, for they seem to be sleepwalking through their undeath. Most aren't aware that they are dead, and even those who know this fact are barely aware of their surroundings, their situation or their own strength.
This half-awake state of being is known as the Fugue. Those who have some insight - however limited - into these matters say that it is caused by the shock of dying. And a ghost might yet outsit an eternity without ever recovering from it, for it is all-encompassing, and powerful: draining away conscious thought and lulling the Ghost to "sleep" as surely as opium.
Sleepers will respond to certain things, such as being attacked, or having their Anchors threatened. But once the threat is gone, or the excitement goes away, they go right back to whatever they were doing before they were interrupted. They may completely forget that it happened, or may conveniently remember it again when something similar happens. Such are the vagaries of the Fugue.
There are a few ways out of this state of affair. Sometimes the directed outpouring of emotion towards a Ghost, or one of her Anchors, is enough to bring her around.  Exceptionally strong-willed Ghosts have also been known to bring themselves out of the Fugue by working through the unreality of their current situation, or forcing themselves to ask questions about the passage of time, and their relation to it. And sometimes Ghosts just wake up, as though the Fugue were nothing more than a long and luxurious nap.
But there is a more direct - if somewhat brutal - way to wake up a sleeping ghost: removing its Shroud.
All ghosts are trapped inside a Shroud, which is a flimsy, ethereal membrane that covers them from head to foot. No one is certain if the Shroud is the cause, or a byproduct, of the Fugue. All that is known for certain is that its presence is integral to keeping the Ghost Asleep, and removing it, then, is the surest, most direct way to Awaken a ghost, thereby creating a Wraith.
And when it's over, and the Wraith is fully aware of what she's "gained," it's quite understandable why many of them wish they'd stayed Asleep.

Means of Demise

The first division in undead society - at least past the matter of being Asleep or Awake - is caused by the last moments of every Wraith's mortal life.
The means by which one dies mark the dead in ways that are both indelible and unquestionable. They provide Wraiths with with the source of their Deathmarks, and an affiliation towards certain Numen. And they also make each Wraith stronger in one regard, yet weaker in another, as though they were caught in some kind of spectral balancing act.
Those slain by Violence are something of an angry breed, hence the nickname of "Ragers," "Redfaces" and "Bruisers." They know too well the cost of anger, and yet they are marked with an odd propensity towards it, reflecting in an increase in their strength. They also become attuned to either controlling fear in others, via the Numen of the same name, or channeling their rage and pain through the strains of Kinesis. And their anger will become all too clear if they are presented with a close reminder of how they, themselves, died, as they may slip into Shadowstate without meaning to.
Meanwhile, those who succumbed to Sickness or Starvation are conversely granted an increase in their stamina, as if to make up for their bodies' failure. These dead are known as "Sickies" and "Plaguebearers," even if they starved to death, due to the horrid miasma of disease and sickness that surrounds them. The experience of having died in this all-too-earthly fashion lends them an affinity towards either the Bios or Embody Numen, as they have either gained an insight into the workings of the human body, or forced themselves to be for so long that Embodying now seems second nature. 
The ones taken by Old Age are often referred to as "Elders" or "Grandparents," when they're not being derided as "Antiques" or "Old Farts." Having forced themselves to live as long as they did increases their resolve, just as having gotten so old makes them more attuned to the Bios or Decay Numen. But they also face the danger of giving up too easily, or falling into a deadly rut - leading to easier Ossification if they're not careful about it.

Happenstance takes many a victim, and grants them an increase in their dexterity as if to make up for the whole thing. They are also granted affinities with Kinesis and Fate, which may give them a better chance the next time around. However, all "Accidents," "Whoopsies" and "Slip-Ups" are also cursed with suffering physical flashbacks to their deaths, both on important anniversaries and in eerily similar circumstances.

The "weirdoes" and "lunatics" who died due to their own Insanity are not often popular, even if they might have a talent for the much-needed Castigate Numina as a result of wrestling with their inner demons. This may be because they can also have a talent for the Fear Numina, instead, or perhaps because their mania followed them even unto death, in the form of a post-mortem insanity that can never be healed. The fact that their composure is raised to help counter this handicap is often lost on those who would judge them.

Also unpopular are those whose deaths are a Mystery, even to them. Bereft of Deathmarks, they stand out like sore thumbs, and could develop a talent for any Numina at all - including ones that are hard to come by, or possibly even unique. Their wits have been sharpened by the uncertainties of their death, but they will need them, for they are compelled to seek out any new evidence of what may have happened. And once the mystery is solved, their proper Deathmarks appear, and they can no longer be referred to as "blanks," "enigmas" or "questions."

But the most unpopular of all are those who died due to the hand of Fate in action - mostly because no one but the "Touched" know who one another are. The "Condemned" sport proper Deathmarks according to how they died, but the why of it revealed only to one another, in a special Deathmark only they can see. The hand of Fate upon them makes them more manipulative, perhaps because they are more attuned to how the world works, and they can have an affinity for either the Fate or Embody Numen along similar principles. But that hand can also be very controlling, and many of the "Puppets" find out that it can control them just as easily, occasionally turning them into automatons and sending them off on some unguessable errand.