Constitutional crisis

 You thought I was gonna get all political, didn't you? But no, I just want to talk about Constitution in basic D&D, and how it's at least a little bit broken.

Constitution, as written in B/X and BECMI D&D, has a much larger impact, for good or ill, than other ability scores. These editions use a modifier scale from -3 to +3. Most modifiers are applied to a d20 roll, meaning they can have, at most, an impact equal to 15% of the die's maximum. That makes a + or -3 modifier nothing to sneeze at, but it's not big enough to render a character either unplayable or insuperable. 

Constitution, though, tacks that -3 to +3 modifier onto rolls of d4, d6, or d8. Despite the huge disproportion, nobody ever complains about piling a +3 on top of a d4 at each level, even though it more than doubles the average hit points of such a character (2.5 base, 5.5 after +3 modifier) and it's not really a huge deal to have an exceptionally hale and hearty magic-user have more hit points than a fighter of average fortitude. Where it gets dodgy is in the penalties. A -3 means a magic-user or thief unfortunate enough to have a Con score of 3 gets 1 hp per level, full stop. That's less than half the average per die for a character of 9-12 Constitution.

Many, if not most, DMs probably hand-wave the problem away by using some method of character creation that seldom produces below average scores, let alone in the dismal 3-5 range, or else allows a character with very low Constitution to be declared "hopeless" so the player can roll another one. Others might tell the player just to go with it, secure in the knowledge the character won't last long and an opportunity to roll up a better one is right around the corner.

But that's suboptimal in my mind. After all, the mere existence of the low end of the ability score scale implies that low scores, even very low ones, are an expected part of the game, and when merely rolling one renders a character nearly unplayable, it's a problem. This isn't some edge case where a perfect storm of bad rolls cripples a character's playability; this is one little ability score that can make an already fragile d4 hit die into a snowflake with an automatic maximum of 1 hp per level. 

Can we mitigate this a little without resorting to Rule Zero kludges or ugly math that breaks the neat, simple symmetry of B/X ability adjustments? Yes, I think we can. The simplest solution is to assign a maximum adjustment based on the size of the die: +/-3 for a d8, +/-2 for a d6, and +/-1 for a d4. 

Here's how it breaks down vs. a strict by-the-book application of the -3 penalty.

Hit Die	Average and maximum per die, by the book, Con 3	Average and maximum per die, scaled penalties by die type, Con 3
d4	1.00 / 1	1.75 / 3
d6	1.50 / 3	2.00 / 4
d8	2.25 / 5	2.25 / 5

With the scaled penalties, a very low Constitution is still a major handicap, but less crippling, especially for the lower Hit Dice classes. A 3 Con is now most harmful to fighters, and indeed, rolling such a score should give one pause about pursuing melee combat as one's vocation, yet it still leaves a 3-Con fighter with more hp on average than other classes with the same score, if a player should choose to do so. 

Whether you apply a symmetrical dice-scaling bonus for high scores, or continue to use the bonuses by-the-book is up to individual taste, but at least a character with a 3-5 in Constitution is no longer utterly hopeless.