What's the difference between a ranger and a druid? A ranger and a barbarian? A fighter and a warlord? A paladin and a cleric?
I /know/ it's rhetorical, but I just can't help trying to answer:
[sblock="gratuitous comparisons"]Let's look as Sorc v Wiz. What's the difference:
AD&D: 9th level magic-user vs 11th level magic-user
3e: How they cast spells. Spontaneous vs Vancian.
4e: Role. Striker vs Controller; Class features. 'Soul' (different features for each build) vs Implement Mastery/Cantrips/Spellbook; Spell lists: Hundreds of spells for each class, none shared.
5e: Class features. Spellbook vs known spells; metamagic vs schools; &c.
Also: not in Basic vs in Basic.
OK, lets do the rest of them:
Ranger vs Druid
AD&D: Woodsy fighter who tracks and casts a few magic-user spells vs Woodsy priest who Shapechanges and has lots of spells over 3rd level but caps at level 14. Totally different exp tables. Different attack & save matrixes
3e: Class features: Full BAB vs 3/4; half-caster vs Full Caster; Favored Enemy vs Shapechange; Spell lists with some overlap.
4e: Source: Martial vs Primal; Role. Striker vs Controller; Class Features: Hunter's Quary, Prime Shot, Fighting Style vs Balance of Nature, Primal Aspect, Wildshape. Completely different lists of hundreds of exploits vs hundreds of invocations.
5e: Class Features: half-caster vs full caster; wildshape vs TWFing & tracking - honestly the playtest ranger didn't make much of an impression...
ranger vs barbarian
3e: class features: half-caster vs Rage, bonus feats vs uncanny dodge..
4e: Source: Martial vs Primal; Class Features: Hunter's Quary, Prime Shot, Fighting Style vs Agility, Feral Might, Rage Strike, Rampage. Completely different lists of hundreds of exploits vs hundreds of invocations.
5e: Class Features: half-caster vs Rage
fighter vs warlord
AD&D: existed vs didn't exist.
3e: existed vs didn't exist.
(Or, if you take the Marshal as Walord, class features: full BAB vs 3/4, bonus feats vs auras)
4e: Role: Defender vs Leader; Class Features: Fighting Style, Combat Superiority, Combat Challenge vs Combat Leader, Inspiring Word, Commanding Presence; Different lists of hundreds of exploits unique to each class.
5e: exists vs doesn't exist.
(Or, if you take the Battlemaster as both 'complex' fighter and Warlord: 14 maneuvers vs 2.)
paladin vs cleric
AD&D: half-caster vs full caster; lay on hands vs full-power turn undead; different attack & save matrices, different weapons permitted.
3e: Class features: Full BAB vs 3/4, half-caster vs full caster, save bonus & lay on hands vs domains
4e: Role: Defender vs Leader; Class Features: Divine Challenge, Lay on Hands vs Healing Word, Healer's Lore, Ritual Casting. Different lists of hundreds of prayers each.
5e: Class Featuers: half caster vs full caster, Pally/Warden/Blackguard vs Deity/Domain[/sblock]
The harder questions are: What's the difference between a Ranger and a Fighter/Druid or a Barbarian and Fighter with a 'barbaric' background or a Paladin and a Fighter/Cleric.