How Guild Magic Works

Guild Magic is based on using the smallest non-sentient Spirits that exist in and around everything. Guild Magic directly Manipulates Spirits through precise hand motions, each representing different symbols or numerals. Directly manipulating Spirits in this manner requires at least one hand to be free; two if using the Guild Magic feat.
In the game setting of Sarru Adnati, Guild Magic is explicitly taught only to women, and they are naturally more talented at it, but male characters can learn it through other means.
The Guild Magic feat tree (includes the Guild Mage, Guild Sister, and Guildmistress feats) allows the user to learn new sets of spells by casting the Grant Ability spell and taking the Spellcaster or Divinity feat. This normally is not allowed (Grant Ability usually only allows players to take combat feats) and there are limitations to the level of the spell and what may be done with them that are reduced or removed by taking the other feats in the tree.
The mechanics of the Guild Magic feat tree are designed to represent how highly trained Guild Mages Cast Spells. Rather than mastering a set of memorized hand motions, those with the Guild Magic feat make each spell from scratch depending on the circumstances. This process requires much more fine-tuned control, and therefore needs both hands available to use.
The form of Guild Magic that is taught in the Arcanum Guild is based on a cuneiform writing system for symbols and a duodecimal (base 12) system shown through pointing to one of the three finger joints on each finger with a thumb (with the base of the pointer being 1 and the tip of the pinky being 12). Every element (periodic table up to Lead) and a set of 12 reactions have a symbol, and the symbol is either drawn in the air or on the palm of the hand.