To elaborate on Meophist's diagram:
If F, C, T ,W are the four basics, but I don't think they're a spectrum. They're four independent roles--fighting, support, skilling, and magic.
(4E recognized something similar about combat roles, but IMO they gave the combat role too much importance. A class should be about what the PC does in the world, not how they operate tactically.)
So I think the core classes should be designed around these four poles and possible hybrids, but the hybrids also need a convincing role in the world. Also, the poles can contain more than one class each; after all, they're pretty broad categories.
So here's how I see the relationship between classes: the poles are on the corners of a square, and the hybrids on the edges and diagonals.
POLE: MARTIAL
Fighter, Warlord, Barbarian
POLE: DIVINE
Cleric (low-magic cleric), Priest (high-magic cleric) Druid, PF Oracle (spontaneous caster)
POLE: SKILL
Rogue, Assassin/Spy, Arcana Unearthed Akashic
POLE: ARCANE
Wizard, Sorceror/Warlock
HYBRID: MARTIAL/DIVINE
Paladin
HYBRID: MARTIAL/SKILL
Ranger
HYBRID: MARTIAL/ARCANE
pick your favorite Gish. Mine is the Mage Blade from Aracana Unearthed.
HYBRID: DIVINE/SKILL
Inquisitor? Monk?
HYBRID: DIVINE/MAGIC
Pathfinder Witch or Summoner
HYBRID: SKILL/ARCANE
Bard