Enchanted Realms Rulebook
While much of sorcery is mental, nearly all spells require verbalization of arcane words to ensure the proper magical threads combine for the effect. However, not every axiom requires speaking, meaning a few can be cast in the midst of a silence effect, similar to the limitation with divine powers. Further, many axioms will also require physical gesturing to help with the manifestation. And finally, occasionally some sorcery will rely upon external components. Scry is one such example. All of this is address specifically for those who subdue a sorcerer to better understand binding hands and gagging the caster will prevent spell-usage in most cases.
On the flip side, the requirements may also determine whether the sorcerer can perform his or her magical in secret. Verbal intrinsics of an axiom must be annunciated distinctly and at a normal speaking volume; therefore, casting such spells clandestinely in virtually impossible. However, gesture-only axioms may sneak by observers. Those in combat will notice spells almost automatically, unless the GM rules a condition such as blindness or other circumstance. However, for those casually observing the area can notice a gesture-only spell during a non-combat social scenario by making a normal Perception check (DC:11). If the caster has the stealth and is specifically attempting to hide the action, then the Difficulty is raised to 13. If using stealth to completely conceal oneself, then the normal stealth DC is used to know the caster is even there; however, that would really be a non-combat social scenario.
Also, if the axiom requires only a gesture but the sorcerer is shackled, bound or otherwise restrained, then there is still a very small chance the caster might manifest the spell, assuming the other factors are not inhibited. In such a case, if the sorcerer can made a Mind feat check (DC:20), then the spell can occur. The GM might adjust appropriately for the knots skill or other circumstances. However, if failing the casting, the spell points attempted will be lost. Further, maintaining concentration, if needed (see below), may also be adjusted by the GM. Finally, mental-only axioms, which tend to fall into the detection category, cannot be observed without magical aid. Further, mental-only effects are extremely difficult to prevent; however, captors have been known to render sorcerer's unconscious or even strike them with a weapon of nonsense to prevent casting.