Sorcerers control spirits (associated with natural places and animals) and ghosts (the souls of dead sapient beings). They are an unusual by product of Illyria's history.
In the Old World, binding souls is strongly discouraged, as it is associated with the dark necromancy of the Night Walkers, a civilization destroyed by the Empire of the North.
(There is a big tradition of binding souls VOLUNTARILY in the Eastern Empire, where revered ancestors may be bound into household shrines and honored as a way of easing their reincarnation into a higher form. In the North, people might talk to the dead by allowing spirits to possess them--but in doing so they would making themselves vulnerable to the dead.)
Because refugee Night Walkers were the first Humans and Goblins to settle Illyria, the tradition of soul-binding came to the New World. There it conflicted with the indigenous Shamanism, which negotiates with spirits and accepts possession by them rather than binding them.
When the Western Empire began to found it's Illyrian colonies, it wiped out the Night Walker pockets that it found, the last being found in what are now the Green Kingdoms. To fight the Night Walkers as well as hostile indigenous cultures (who opposed the new colonizers as they had the old invaders), the Imperials found it necessary to accept sorcerers into their own forces to counteract the spirit magic they encountered.
Once the wars of conquest were over, the Western Empire made sorcery legal under certain limits. Only the Wardens of the Western Forest, the personal Huntsmen of the various Illyrian Kings and High Nobles, and the masters of the Shadow Guild may bind human souls, and only those of convicted criminals and traitors. All other spirits used by sorcerers are to be those of animals or "lesser" species such as Great Wolves, Hents, or on rare occasions Trolls.
However, there is always talk of rogue sorcerers who disobey these bans. Typically they commit their soul-binding crimes in one locale and flee to another to sell their services to unscrupulous employers.
Whereas the Dragon-Blooded are typically taught by the Human and Dragon tutors of their own Noble Houses, with various manuals of instruction being produced for each House, sorcery is a more mysterious and secretive art. Outside of the Wardens, Huntsmen, and Shadow Guild, it is only taught by one master to one apprentice at a time.