Tuesday, December 15, 2015

Ability Score Minimums in B/X (Part 1)

At the end of my post on strict spell books I complained that B/X allows magic-users that cannot read. To quote:

I noticed that B/X interprets low intelligence scores as a limited ability to speak/read/write. However, magic-users are not required to have a minimum intelligence score. This either implies magic-users who can be almost braindead yet cast Fireball or a missing minimum requirement. I am about to house-rule that magic-users need a minimum intelligence of 9 just like elves.

Now I've finally had time to think through what such a minimum requirement would mean. And I have to admit that I was somewhat surprised when I found out that it means almost nothing.

Let's assume that the B/X world is populated with "3d6 in order" humans only. What's the chance of rolling a 9 or greater on 3d6? Answer: 74.07% So almost three quarters of all attributes will be 9 or greater.

Now if I wanted to add a minimum intelligence requirement for magic-users, I should probably add one for clerics, fighters, and thieves as well, right? So let's say that all four human classes have such a minimum requirement. What's the chance that out of the four rolls determining strength, intelligence, wisdom, and dexterity not a single one would be 9 or greater?

Let me not bore you with the math, it turns out to be 0.45%. So out of a million humans, roughly 4,500 would no longer be able to qualify for any class. Yes, it's tough, those 4,500 would have to remain "normal humans" for the rest of their lifes.

Not trusting my math I hacked a quick Python script to roll up characters and evaluate them, so we can actually look at a sample of these poor sods:

{'C': 6, 'D': 4, 'I': 8, 'S': 8, 'W': 8, 'X': 11}
{'C': 12, 'D': 7, 'I': 8, 'S': 8, 'W': 7, 'X': 11}
{'C': 17, 'D': 8, 'I': 8, 'S': 7, 'W': 7, 'X': 13}
{'C': 7, 'D': 5, 'I': 6, 'S': 7, 'W': 6, 'X': 10}
{'C': 9, 'D': 8, 'I': 8, 'S': 4, 'W': 8, 'X': 12}
{'C': 8, 'D': 6, 'I': 8, 'S': 8, 'W': 8, 'X': 17}

Some have "redeeming" features, take the one with a constitution of 17 and a charisma of 13 for example. Presumably there is a player somewhere who'd have fun playing this character: A healthy and charismatic (leader-type?) magic-user who has a hard time writing down notes. But let's be honest, just how many players are we talking about here?

So here's my verdict: Adding a minimum requirement of 9 for the prime requisite of a class is totally fine. True, if we look at individual cases, there may be some characters that we could still find a player for. Overall, however, I don't see how 0.45% of rolled up characters contributing to nothing but entropy are a problem. I'd much rather be sure that magic-users can actually speak/read/write, that fighters can actually carry their armor and weapons into battle, etc.

Appendix: Once I had the Python script, I couldn't resist running it a few more times. Say we wanted to make sure that characters are actually good in their chosen class by requiring a 13, what would that mean? How about requiring 16? Here are the results for each 9, 13, and 16 when generating a million characters:

 Prime Requisite

Obviously the higher minima have a huge impact on who can join a class and who has to remain a "normal human" as it were. Those higher minimums are certainly not recommended for standard B/X, although I have a feeling they'll help me in my house rules regarding multi-classed characters.


  1. You might argue that a "soft limit" is implied by the bonus/penalty to the experience points rewarded: a character with a prime requisite score lower than 9 will receive at most 90% of the XP. In practice, I feel this is sufficient motivitation to not play that character class.

    1. It's correct that the XP adjustment mechanic does encourage and discourage certain class choices. I should have stated somewhere in my post that I don't particularly like that mechanic because of the added bookkeeping. Minimum ability scores seem much simpler to me. But as far B/X as written, your point is well taken.

  2. I kinda looked at this a while back. In the end you need to accept that demihuman deviation from the human bell curve is either:
    (a) because they are 'alien' and don't conform to human limits, or
    (b) because they are 'an isolated culture' that's been throwing babies down a hole when they show any kind of nonconformity to a culturally preferred type.
    The idea that elves infect their children with bark pox to cull the ones with less than 12 constitution puts a Spartan spin on elves that offends players who like elves to be 'nice'.

    1. Elves require intelligence 9 not constitution 12. I know, that wasn't your point. I am just a stickler for correctness. :-) For the record, I don't need nice elves, indeed I'd be fine with elves enslaving humans or whatnot. But I have trouble with any culture that would throw kids into holes, doesn't matter what the reason is. So I guess I am culturally insensitive in a way.

  3. I consider magic a language. This means a wizard and elf need a language slot to allocate. So you want to Learn magic? 13 intelligence required. How do we then deal with Clerics? A 13 intelligence as well? That makes Clerics even rarer than wizards.

  4. It's recommended you Revolt your abilities if two or more abilities are less than eight. That's a large percentage of the bell curve right there.