A character may add new classes as he or she progresses in level, thus becoming a multiclass character. The class abilities from a character's different classes combine to determine a multiclass character's overall abilities. Multiclassing improves a character's versatility at the expense of focus.
Class And Level Features
As a general rule, the abilities of a multiclass character are the sum of the abilities of each of the character's classes.
"Character level" is a character's total number of levels. It is used to determine when feats and ability score boosts are gained.
"Class level" is a character's level in a particular class. For a character whose levels are all in the same class, character level and class level are the same.
A character gains hit points from each class as his or her class level increases, adding the new hit points to the previous total.
Base Attack Bonus
Add the base attack bonuses acquired for each class to get the character's base attack bonus. A resulting value of +6 or higher provides the character with multiple attacks.
See Fractional Base Bonuses
Add the base save bonuses for each class together.
See Fractional Base Bonuses
A character got access to all skill groups from all of his classes. (The maximum rank for a class skill is 3 + character level.)
A multiclass character gets all the class features of all his or her classes but must also suffer the consequences of the special restrictions of all his or her classes. (Exception: A character who acquires the barbarian class does not become illiterate.)
In the special case of turning undead, both clerics and experienced paladins have the same ability. If the character's paladin level is 4th or higher, her effective turning level is her cleric level plus her paladin level minus 3.
In the special case of uncanny dodge, both experienced barbarians and experienced rogues have the same ability. When a barbarian/rogue would gain uncanny dodge a second time (for her second class), she instead gains improved uncanny dodge, if she does not already have it. Her barbarian and rogue levels stack to determine the rogue level an attacker needs to flank her.
In the special case of obtaining a familiar, both wizards and sorcerers have the same ability. A sorcerer/wizard stacks his sorcerer and wizard levels to determine the familiar's natural armor, Intelligence score, and special abilities.
A multiclass character gains feats based on character levels, regardless of individual class level
A multiclass character gains ability score increases based on character level, regardless of individual class level.
The character gains spells from all of his or her spellcasting classes and keeps a separate spell list for each class. If a spell's effect is based on the class level of the caster, the player must keep track of which class's spell list the character is casting the spell from.
See Magic Ratings for Standard Characters
Orfinlir does not use favored classes and xp-reduction based on level difference between two classes of a character
That said, there are surely classes, that fit better to a race and reasons to not allow a player to add another class to his character.
The following restrictions allways apply:
- Dwarves can not use arcane magic (neither sorcerous nor wizardly).
- Only under special circumstances can a character take barbarian as a second class. (such as has lived amongst barbarians for a long time or is a barbarian but took a different class first)
- Some classes are not available to some races or in some ages (like the rune-crafter, which is always available to dwarves but only since 1400 nDF to characters belonging to the Middle Hillsites; or some racial/ national variants).
- There must be a good reason, why a character takes a new class and it must be plausible, that he somehow aquired the abilities (like training for some time or living with someone of that class)