Q. Are all of the attributes having required minimums to be construed as “principal attributes” for that class with regard to two-classed characters?
A. Yes, with two exceptions. For the purpose of determining whether a character is eligible to take up a second class, principal attributes for each class are considered to be these: cleric, wisdom only; druid, wisdom and charisma; fighter, strength only; paladin, everything but dexterity; ranger, everything but dexterity and charisma; magic-user, intelligence only; illusionist, dexterity and intelligence; thief, dexterity only; assassin, dexterity, intelligence, and strength; and monk, everything but charisma and intelligence. This includes every ability for which a required minimum is given, except for the fighter’s constitution, which must be at least 7, and the magic-user’s dexterity, which the Players Handbook says must be at least 6. The first exception is made because “The principal attribute of a fighter is strength,” but constitution isn’t mentioned in the same sentence (PH, page 22). A “minimum dexterity of 6” is required for magic-users (page 25), but this is superfluous, since a character with a dexterity of 5 or lower is always a cleric (page 11). Note that the principal attribute(s) for each class may include abilities in addition to those that apply toward a bonus to earned experience. To limit the definition of “principal attributes” to only those abilities that pertain to the experience bonus would make the system unbalanced and unplayable — unbalanced because then it would be easier to become a two-classed paladin than a two-classed ranger, and unplayable because the assassin and monk never get an experience bonus, and so by this definition would not have any “principal attributes.”
Source- Dragon Magazine #64, Sage Advice (again, these are official).
Again, I enjoy good rules discussions, but at a certain point don't people realize that I put in a little work before making pronouncements? Are people just into torturing me?: