Ability Point Swapping and Experience Bonuses in Men & Magic

On p. 10 of Men & Magic Gary Gygax explained how characters could use points from another ability score to increase their score in the class prime requisite “for purposes of gaining experience only.”  Though later editions—Holmes and Moldvay—had a mechanism for the actual swapping of points, I think the consensus on what Gygax meant in Men & Magic is that the mere existence of average to high scores in certain abilities meant that one might get a bump up in one’s prime requisite for the purpose of computing the experience point bonus or penalty. (Why I think this is the consensus, and why I think the consensus is correct is another question, but I do not intend to argue for it here.)

The experience point bonus/penalty numbers look like this:

Modified Prime Requisite Score	Experience Point Bonus/Penalty
3-6	-20%
7-8	-10%
9-12	0
13-14	+5%
15+	+10%

All classes have a prime requisite ability score and a secondary ability score.  All except Magic-users have a tertiary ability score.  The chart below summarizes things and includes the character class of Thieves from the first supplement:

Class	Prime Requisite	Secondary Ability	Tertiary Ability
Cleric	Wisdom	Intelligence	Strength
Fighter	Strength	Intelligence	Wisdom
Magic-user	Intelligence	Wisdom	None
Thief	Dexterity	Wisdom	Intelligence

Clerics, Fighters and Magic-users can use their secondary score to add 1 point to their prime requisite (again, only for the purpose of computing the experience bonus/penalty) for every 2 secondary score points above 9.  Fighters and Clerics can add 1 point for every 3 tertiary score points above 9.  Thieves have slightly different rules—they can trade 1 secondary score points and 2 tertiary score points for 1 prime requisite point.  (Presumably this is a package deal—if one’s secondary score was, say, 9 or below, one simply couldn’t trade in any tertiary points, even if one had a tertiary score of 18.)

For the heck of it I created these charts:

Clerics—Bonus Points Added to Wisdom

(For Purposes of Gaining Experience Only)

↓Strength                       Intelligence→
	1-10	11	12	13	14	15	16	17	18
1-10	0	+1	+1	+2	+2	+2	+3	+3	+4
11	0	+1	+1	+2	+2	+2	+3	+3	+4
12	+1	+2	+2	+3	+3	+3	+4	+4	+5
13	+1	+2	+2	+3	+3	+3	+4	+4	+5
14	+1	+2	+2	+3	+3	+3	+4	+4	+5
15	+2	+3	+3	+4	+4	+4	+5	+5	+6
16	+2	+3	+3	+4	+4	+4	+5	+5	+6
17	+2	+3	+3	+4	+4	+4	+5	+5	+6
18	+3	+4	+4	+5	+5	+5	+6	+6	+7

Fighters—Bonus Points Added to Strength

(For Purposes of Gaining Experience Only)

↓Wisdom                       Intelligence→
	1-10	11	12	13	14	15	16	17	18
1-10	0	+1	+1	+2	+2	+2	+3	+3	+4
11	0	+1	+1	+2	+2	+2	+3	+3	+4
12	+1	+2	+2	+3	+3	+3	+4	+4	+5
13	+1	+2	+2	+3	+3	+3	+4	+4	+5
14	+1	+2	+2	+3	+3	+3	+4	+4	+5
15	+2	+3	+3	+4	+4	+4	+5	+5	+6
16	+2	+3	+3	+4	+4	+4	+5	+5	+6
17	+2	+3	+3	+4	+4	+4	+5	+5	+6
18	+3	+4	+4	+5	+5	+5	+6	+6	+7

Magic-users—Bonus Points Added to Intelligence

(For Purposes of Gaining Experience Only)

Wisdom→
1-10	11	12	13	14	15	16	17	18
0	+1	+1	+2	+2	+2	+3	+3	+4

Thieves—Bonus Points Added to Dexterity

(For Purposes of Gaining Experience Only)

↓Wisdom                       Intelligence→
	1-10	11	12	13	14	15	16	17	18
1-9	0	0	0	0	0	0	0	0	0
10	0	+1	+1	+1	+1	+1	+1	+1	+1
11	0	+1	+1	+2	+2	+2	+2	+2	+2
12	0	+1	+1	+2	+2	+3	+3	+3	+3
13	0	+1	+1	+2	+2	+3	+3	+4	+4
14	0	+1	+1	+2	+2	+3	+3	+4	+4
15	0	+1	+1	+2	+2	+3	+3	+4	+4
16	0	+1	+1	+2	+2	+3	+3	+4	+4
17	0	+1	+1	+2	+2	+3	+3	+4	+4
18	0	+1	+1	+2	+2	+3	+3	+4	+4

What this shows, among other things is that under what we might call the virtual point swapping scheme, it’s pretty darn difficult to get a set of scores that will produce experience penalties, and conversely it is not very difficult to get a set of scores that will produce bonuses.  This is due to the fact that even with a low "raw" prime requisite score, the odds are that you'll be saved by one or more bonuses from your secondary or tertiary scores.

Combining the above charts together with the bell-curve odds of the prime requisite score, here are the odds for the range of experience bonuses and penalties for someone who, before rolling 3d6 in order, has it in his mind to choose a particular class:

Experience Bonus/ Penalty	Cleric	Fighter	Magic-user	Thief
+10% or better	20%	20%	19%	12%
+5% or better	39%	39%	33%	31%
-10% or worse	19%	19%	27%	23%
-20%	6%	6%	13%	8%

So if you know you want to play a particular class, there's a 30-40% chance you will roll up scores that will give you at least a small experience bonus and a 70-80% chance that you will avoid any experience penalty.

But if you are prepared to play any of the four classes, then the odds of rolling up a character who gets the highest experience bonus of +10% are better than even, and the odds of rolling up a “hopeless” character who will suffer a penalty are extremely low—about 1 in 500 for the -10% penalty and 1 in 30,000 for the -20% penalty!!!

Who said rolling 3d6 in order was such a bad deal?