Psionics could be viewed the same way, but in my mind, there's more of a conceptual backing. Wizardry (standard magic) is external (manipulate magical forces or auras;) Psionics is internal (mental forces.) Thus, psionics doesn't require words, gestures, or ingredients (external components,) but can't maintain an external existence on its own (requires conscious thought.) There are a number of conclusions you can draw from this distinction:
- Because psionics are internal, they rely on the psychic's own power, and are fatiguing;
- It's possible to run out of psionic power, but it's also possible to use psionics at-will;
- Psionics can't be maintained without a conscious psychic backing them;
- Internal power can only be disrupted by internal actions, such as successful mental attacks or Confusion effects.
See the difference? You can start with the basic assumption of "psionics is internal (pure mind power)" and evolve a number of details from that. But sorcery, as typically presented, isn't differentiated from scholarly magic. I think there's the potential that it *could* be. Consider Wizardry and Psionics as two extremes, with Sorcery somewhere in the middle. Sorcery could be more like psionic manipulation of magical force, sort of a bridge between the external and internal. Sorcerous spells can be maintained without concentration, but there's still a personal connection; I would definitely make sorcerous enchantments end when the sorcerer dies, which matches the way magic sometimes works in legend and literature. Because the sorcerer manipulates an external magical force, sorcery relies on a physical substance: burning incense, spilling blood; each sorcerer would have a particular style. This is distinct from the wizard, who (by default) only uses spell ingredients during preparation, not when triggering the spell.
The sorcerer relies on personal power rather than knowledge of formulas, so sorcerers would not require books, but would start with fewer spells. It should be more difficult for them to acquire new spells; perhaps they should be limited to a number of spells equal to double or triple their level, but they would be able to cast these spells multiple times per day, within the limits of how much incense (or blood, or other substance) they have left; also, sorcery should be exhausting, but not as much as psionics.
Incidentally, I'm seeing the illusionist as being somewhere on this same wizardry/psionics continuum, but closer to the psionics end, compared to the sorcerer, who is closer to the wizardry end. This may mean that illusionists should not have limit on how many illusions they can create per day, but can become mentally exhausted faster.