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:

Minimum  Prime Requisite	Classed Humans	Normal Humans
9	995,372	4,628
13	699,147	300,853
16	173,279	826,721

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.