Example Traditions:
- Glamour (illusions, enchantments, "fey stuff")
- Gnosis (self-imposition, willpower, "psi stuff")
- War (direct combat evocations & conjurations)
Each spell here has exactly one Tradition, and at least one Keyword.
Barkskin
Tradition: Glamour
Keywords: Wood
Blindness
Tradition: War
Keywords: Hex, Illusion
Calm Emotions
Tradition: Gnosis
Keywords: Light, Stasis
Glitterdust
Tradition: Glamour
Keywords: Light
Gust of Wind
Tradition: War
Keywords: Air, Storm
Hold Person
Tradition: Glamour
Keywords: Archon, Hex, Stasis
Invisibility
Tradition: Glamour
Keywords: Air, Illusion, Subtle
Mirror Image
Tradition: War
Keywords: Illusion
Resist Energy
Tradition: Gnosis
Keywords: Abjuration, Stasis
Scorching Ray
Tradition: War
Keywords: Fire
See Invisibility
Tradition: Gnosis
Keywords: Archon, Divination, Dragon
Silence
Tradition: Glamour
Keywords: Air, Hex, Subtle
Wind Wall
Tradition: War
Keywords: Air, Archon
So, what does this do for us? Well, you could make a "traditional" class, like a Warmage, and give them everything in the War tradition. That would work. (If you only had those 3 casting classes, you'd effectively create a Disjoint Access game using Descriptor Access rules.)
You could make classes that grant access across traditions, by keyword, like a Monk of the East Wind, who gets access to all Air spells.
You could make a Winter Witch, who gets all spells with at least one of: Divination, Hex, Illusion, Cold.
You could make a feat like Disciple of the Archons, which adds access to all Archon spells. ("Archon" is an abstract keyword that exists primarily to hang other effects on.)
You could also modify access by saying: "You follow a Chaos god. You are prohibited from casting any spell with the Archon or Stasis descriptor."