Paths of the Eldar
After the Fall of the Eldar and the birth of Slaanesh, the surviving Craftworld Eldar realized that their emotions were too potent to be allowed to run free. To control their emotional extremes, the craftworlds formulated the Paths of the Eldar, a series of goals and occupations that would leave the Eldar emotionally regimented to avoid falling prey to She Who Thirsts. Individually, these paths are reminiscent of an autistic obsession. Collectively, the Paths are like a form of multiple personality disorder, where an Eldar will learn everything they can about one role or task, shut it off from their mind when not needed, and reopen it when needed. It is, however, possible to reach a point where an Eldar becomes "lost on the Path", meaning that they cannot shut off that particular aspect of their personality to the exclusion of all others. There are a number of known Paths that can be walked.
Path of Awakening
On this path, an Eldar will learn to better analyze their surroundings. This allows them to see things that others would ignore or dismiss as irrelevant.
Path of the Artisan
This is among the most common Paths, where an Eldar learns to make breathtaking works of art. There exist a number of sub-paths, such as the Path of the Poet, the Path of the Sculptor, etc.
These sub-paths do not necessarily mix well with others. The Path of the Poet, for instance, is about writing introverted fanfics that no-one is supposed to read, and so the author can become very apprehensive at allowing others to read them. Some Eldar also use it as impromptu psychiatric therapy, as demonstrated by Farseer Thirianna.
By contrast, the Path of the Sculptor is highly extroverted, and wants everyone to see their work, but can act like a diva even when fairly criticised.
Path of Command
Also known as the Path of the Leader, this is the path that focuses on leadership of other Eldar. Those on the Path of Command become Autarchs, the Eldar equivalent of admirals or generals.
Interestingly, this path can be planned, rather than occurring naturally as an Eldar accumulates experience from various paths. One can arrive at an Aspect Shrine and make it known that they intend to become Autarchs, and they will have a slightly different, more insightful mindset compared to their compatriots within the squad rather than the one imposed on them by the temperament of their chosen Aspect.
Path of the Dreamer
A meditative Path where the Eldar learn to try and control their dreams. Since dreams can often come from the Warp there are probably practical purposes to this, such as using this to predict the tides of the Warp or aid Seers in future sight. Often another Eldar will stand vigil as a "Dream Watcher". The Path of the Dreamer also helps to focus the precision of an Eldar's memory, and they can take mind altering substances to aid them while doing so. Though to others it seems like they are wasted stoners who do nothing but lay about all day.
Ironically, those lost on the Path of the Dreamer, called the Everdreaming, will have difficulty telling the difference between the past and the present.
Path of Grief
"Why do you cry?"
"He is Conan, Cimmerian. He will not cry, so I cry for him."
- – The 1982 Conan the Barbarian movie
A Path taken when the Eldar remember their fallen (of whom there are A LOT) and allow themselves to feel grief without risking the attention of She Who Thirsts. The Eldar on this path will sometimes grieve for someone who cannot be allowed to grieve at this time.
Path of the Healer
Opposite to the Path of the Warrior, Healers are your basic doctors and/or nurses but are also psykers, though of a very specific focus in that they heal Eldar souls and are heavily tied to Isha. Their mythology involves Asuryan tying locks of Isha's hair into Eldanesh's hair so his descendants could be healed with the Power of Love.
Path of the Mariner
These are Eldar who have taken to serving on vessels of the Eldar fleets (craftworlds are too large and unmaneuverable to qualify as capital ships). Unlike the ships of the Imperial Navy, which are crewed by press-ganged slave labour *BLAM*WHICH ARE CREWED BY BONDSMEN WHO ARE HONOURED TO SERVE THE VESSELS OF THE IMPERIUM, the Mariners are eager volunteers who can leave at their discretion.
Path of the Merchant
Mentioned by Gav Thorpe on a Q&A on his blog. This path exists to cultivate and control the Eldar urges to acquire material wealth and collect exotic possessions. However, since those on the Path of the Artisan just give their stuff away since they create merely out of the desire for creation, the Eldar economy presumably works radically differently (space commies) from that of your typical human society.
Path of the Outcast
Not exactly a Path, these are Eldar who have rejected the regimented ways of the Paths and left their craftworld. Often it's caused by wanderlust, rejection of authority, etc. Those on the Path of the Outcast often become Rangers, serving as scouts for Eldar warhosts. In some cases, Eldar who remain on the Path of the Outcast too long end up cutting all ties with the Paths, essentially becoming a full-fledged Dark Eldar.
Path of the Seer
The Path of the Seer is the most treacherous of the Paths, where an Eldar develops their psychic abilities. The Eldar as a species are psykers by nature, but few develop their powers to the level of the Seers. Seers are vitally important to the survival of a craftworld, as they can study the flow of fate to predict what dangers the craftworld will face. Seers gather together to form Seer Councils, groups which form the leadership of a craftworld. Special types of Seers exist, such as Bonesingers, who manipulate Wraithbone, the core component of Eldar constructs. Warlocks are those who have previously served as warriors in an aspect of Khaine, and can become some of the most potent battlefield psykers in the galaxy.
Those who become lost on the Path of the Seer become Farseers, individuals who can see incredibly far into the future. Eventually, the psychic power within the Farseer will overwhelm his or her body and turn it to crystal, and they become another node in their craftworld's Infinity Circuit. Unlike the other paths, those who become Farseers usually choose to become trapped on the Path of the Seer for the sake of their craftworld.
Path of Service
Butlers, housemaids janitors, valets, general dogsbodies; everybody needs them. Since participation in the Path system is largely voluntary (if you don't like it, leave) Eldar on this path must have a burning desire to get those stubborn stains out.
Either that or they just want see what it feels like to NOT be an arrogantly superior prick for a change and start scrubbing toilets and washing dishes. That said, the path of service is often the best way to get other Eldar to get off their too arrogantly superior prick ass and become an aspect warrior to prove them wrong.
Path of the Warrior
Founded by the Phoenix Lord Asurmen after the Fall of the Eldar, the Path of the Warrior is where an Eldar will study at one of the shrines of the Aspect Warriors, learning all they can about their Shrine's skills and methods of waging war. Guardians are not treading the Path of the Warrior, but are civilians taking up arms in reaction to an emergency situation. Eldar following the Path of the Warrior comprise the bulk of their military, and the majority of the pieces in an Eldar army in games of Warhammer 40,000 represent this Path.
Those who become lost on the Path of the Warrior become Exarchs, the priests of the Shrine. Being lost on the Path of the Warrior will end in one of three ways: death in battle, sacrifice as the Young King to awaken the Avatar of Khaine, or becoming the new host for a Phoenix Lord. Should an Exarch die in battle, their personality will live on in their armor. Once donned by another Eldar destined to become an Exarch, the new personality merges with the personalities already within the armor and a new gestalt consciousness assumes the name of the original occupant.