Tribals (and, by extension, Fallen) are very different to the people of the modern day; they’re even different to everyone else in the world in which they live. Unlike us people of the World Before, or Squats, or Serfs, or Keepers, Tribals live between two worlds - the Physical Orb and the River of Dream. Their experience of the world is meaningfully distinct from everyone else’s; their dreams are as often cryptic visions of the future or messages from the spirits as they are strange experiences induced by too much cheese. They live, day by day, in the knowledge that they have a foot in each of two worlds.
It’s the Dream that divides and segregates Tribals from everyone else. It defines their existence and their identity. But their relationship with Dream is also what separates Fallen from Tribals. All Tribals enjoy the Protection of their Eminences, and plenty can Apply them and are even Active Dreamers, however Conjunctional Synthesis (i.e. Intuitive Synthesis, Freeform Synthesis, and Aspects) is very rare amongst the Seven Tribes. Generally only the Priesthoods (Favourites, High Judges, Little Tricksters, Old Ones, Shamans, Sirens, and Templars) receive training in Conjunctional Synthesis, along with certain very favoured other members of the Tribe.
Tribals believe that banishment renders the Fallen incapable of any sort of access to Dream, depriving them entirely of access to their Eminences. In a very great many cases, however, the Tribal belief about the Fallen is demonstrably false. Once Fallen recover from the initial shock and agony of their exile, and they join an Outlook and gain a Second Eminence, many of them start to learn Conjunctional Synthesis. Doomsayers often point to this as being proof of the Prophecy of Joshua, with the Fallen being “dirty, alone and powerful, tied to the Goddess as only they can be”. There are a great many theories about why this is, but little solid evidence of anything.
Eminences are profoundly expressive of a Fallen’s identity. For example, two Jackers, each born into Joan’s Tribe, could have entirely different Eminences. The Jacker with Fury and Vengeance is meaningfully different as a person from the Jacker with Bravery and Devotion - despite being notionally the same in terms of former Tribe and current Outlook. Eminences are best thought of as keywords that describe the high-level concept of a character, and that’s also probably a better way to choose them rather than thinking of them in terms of powers or abilities that they give you.
The most important thing about Synthesis is that it’s not magic in your traditional LRP “point and click” sense. There’s no mind control, and very little direct damage: the “Synthesis” damage call represents Death withering limbs or Force shooting lightning, and “Repel” represents the effect of Motion, but otherwise it is pretty rare for Synthesis to have a visible physical impact.
Synthesis affects the psyche and can allow someone to surpass their normal limitations much more often than it allows the wielder to throw fireballs or do anything particularly showy. Thinking of Synthesis in terms of sorcery is probably a bit misleading: it is generally subtler than that. Aspects are a bit more up-front, or at least can be, but they’re also significantly rarer.
Sundering is much less opaque, being primarily about the manipulation of the physical body: even Z’bri “mind control” is actually them taking control of your body while you watch on helpless. They can certainly affect the soul, but in a very blunt fashion. This critical difference between Synthesis and Sundering is a key thematic point for this game, and one that will probably be more obvious as the campaign progresses.