FrogReaver
The most respectful and polite poster ever
Before you say anything, "Yes, yes, another hit point thread... ARG!"
(Deep breath...)
Okay, so I posted about this in my other thread, but not wanting to derail that I decided to start fresh.
Why do different classes have different HD types?
Now, for the purposes of my question, I am making an assumption that you prescribe to the "abstract" HP camp where HP are a combination of several factors: physical endurance, mental endurance, skill, luck, favor, sixth-sense, etc. If you are in the "HP = meat only (or meat mostly)" camp then larger HD size makes sense for warriors and lower ones for weaker wizardy-types.
You could argue a fighter is "tougher" and can take a beating better, sure, but in the same light I can argue a rogue could have better luck or a wizard a better sixth-sense. Are those weighted less compared to physical endurance? Do you think a battler's skill is superior in combat so they get more HP? Well, wouldn't a caster be better at resisting the damage caused by other spells? HP don't differentiate between the source of the damage, so to say a barbarian gets more HP, even to resist the damage from spells, doesn't make much sense if those HP are earned during a career where the character mostly resisted weapon and natural attack damage.
Also, since front-liners tend to have better Constitution scores anyway because they want more HP, what impact would a flat universal d8 have? Would it hurt them that much, really?
FWIW, I don't really have an issue with HD, this is more about understanding a consistent and logical rationale for different HD sizes if you subscribe to the abstract HP concept.
It seems to me that hit dice gain per level is best thought of as an estimation of your increasing skill. Skill at what you might ask? Well Fighter's increase their skill at fighting, rogues at roguing, wizard and wizarding etc. (Of course hit dice hp are not limited to skill alone).
To me this means the higher hit dice classes are thus more skilled, lucky, etc at defending themselves in combat. Then con increases hp and what it best represents is your ability not to get too tired to effectively defend yourself.