Prime requisite and experience

[bestialwarlust]

So reading through M&M on page 10

"Strength is the prime requisite for fighters. Clerics can use strength on a 3 for 1 basis in their prime requisite area (wisdom), for purposes of gaining experience only. Strength will also aid in opening traps and so on.

Intelligence is the prime requisite for magical types. Both fighters and Clerics can use it in their prime requisite areas (strength and wisdom respectively) on a 2 for 1 basis. Intelligence will also affect referees’ decisions as to whether or not certain action would be taken, and it allows additional languages to be spoken.

Wisdom is the prime requisite for Clerics. It may be used on a 3 for 1 basis by fighters, and on a 2 for 1 basis by Magic-Users, in their respective prime requisite areas. Wisdom rating will act much as does that for intelligence."

People seem to interpret this as reducing one ability to raise another. But reading one can get the impression that you can use the score to determine your experience for prime requisite. So for instance a fighter with a STR of 12 gets no bonus exp. But in reading the above it seems as if you can use Int and Wis to calculate your STR differently. So if my fighter has a STR 12, INT 7, Wis7 I would do the following:

INT 7 (2 for 1) = 3
WIS 7 (3 for 1) =2
Total 5 points

So when calculating experience only I would use the 5 points to my STR and treat it as a 17 STR (though not actually changing the score) which gives me a 10% bonus.

[talysman]

It's how I interpret it, but Holmes Basic turns it into an actual point trade.

[waysoftheearth]

At the bottom of page 11 M&M adds: "...may be used to increase prime requisite total insofar as this does not bring that category below average, i.e. below a score of 9".

So the fighter above with 12 strength, 7 intelligence, and 7 wisdom would have a PR of 12.

If he happened to have an 18 wisdom, then 9 points of wisdom could be used to increase his PR score (not his actual strength score) by 3 pips, from 12 to 15.

[Finarvyn]

This topic comes up from time to time and I've seen folks passionatly argue for either method (actual stat change versus change only for XP purposes).

I've always done it like you (and talysman and ways) suggest -- the actual stats don't change but you use the numbers to fiddle with an extra "prime requisite" stat that is only used for experience calculation.

[bestialwarlust]

Mar 6, 2014 5:16:04 GMT -6 Finarvyn said:

This topic comes up from time to time and I've seen folks passionatly argue for either method (actual stat change versus change only for XP purposes).

I've always done it like you (and talysman and ways) suggest -- the actual stats don't change but you use the numbers to fiddle with an extra "prime requisite" stat that is only used for experience calculation.

Yeah I forgot about the minimum when I was typing up my example.

[bestialwarlust]

Mar 6, 2014 5:16:04 GMT -6 Finarvyn said:

This topic comes up from time to time and I've seen folks passionatly argue for either method (actual stat change versus change only for XP purposes).

I've always done it like you (and talysman and ways) suggest -- the actual stats don't change but you use the numbers to fiddle with an extra "prime requisite" stat that is only used for experience calculation.

I can see why the language can be interpreted in different ways on how it's written.

[makofan]

It makes sense. They are stating that a smart fighter can partially make up for his lack of strength

[Stormcrow]

On the other hand, it seems strange that Gary would speak of bringing an ability below average, rather than "for every X points above 9," if it didn't mean to imply that you're actually reducing the secondary ability.

[bestialwarlust]

Mar 6, 2014 10:57:25 GMT -6 Stormcrow said:

On the other hand, it seems strange that Gary would speak of bringing an ability below average, rather than "for every X points above 9," if it didn't mean to imply that you're actually reducing the secondary ability.

True but it could be looked at as a way to keep a cap on it. In other words you have to have above average scores to supplement your prime requisite.

[talysman]

Mar 6, 2014 10:57:25 GMT -6 Stormcrow said:

On the other hand, it seems strange that Gary would speak of bringing an ability below average, rather than "for every X points above 9," if it didn't mean to imply that you're actually reducing the secondary ability.

On the OTHER other hand, if you took into account scores below average, they should *reduce* your prime score for purposes of experience. And yet... If it is a point trade, why can't Magic-Users trade Strength for Int? Why CAN Fighters trade Into and Wisdom for Strength?

I think the wording is confusing because Gary wasn't sure which way he wanted to go. Eventually, he said "Screw it" and dropped the idea.

[waysoftheearth]

"for the purposes of gaining experience only" is as clear as OD&D gets.

[Stormcrow]

Mar 6, 2014 15:28:09 GMT -6 waysoftheearth said:

"for the purposes of gaining experience only" is as clear as OD&D gets.

Which is to say, not very clear at all. Let's not put more meaning into the phrase than already exists.

[Mushgnome]

Mar 5, 2014 21:53:34 GMT -6 bestialwarlust said:

So reading through M&M on page 10

"Strength is the prime requisite for fighters. Clerics can use strength on a 3 for 1 basis in their prime requisite area (wisdom), for purposes of gaining experience only. Strength will also aid in opening traps and so on.

Intelligence is the prime requisite for magical types. Both fighters and Clerics can use it in their prime requisite areas (strength and wisdom respectively) on a 2 for 1 basis. Intelligence will also affect referees’ decisions as to whether or not certain action would be taken, and it allows additional languages to be spoken.

Wisdom is the prime requisite for Clerics. It may be used on a 3 for 1 basis by fighters, and on a 2 for 1 basis by Magic-Users, in their respective prime requisite areas. Wisdom rating will act much as does that for intelligence."

People seem to interpret this as reducing one ability to raise another. But reading one can get the impression that you can use the score to determine your experience for prime requisite. So for instance a fighter with a STR of 12 gets no bonus exp. But in reading the above it seems as if you can use Int and Wis to calculate your STR differently. So if my fighter has a STR 12, INT 7, Wis7 I would do the following:

INT 7 (2 for 1) = 3
WIS 7 (3 for 1) =2
Total 5 points

So when calculating experience only I would use the 5 points to my STR and treat it as a 17 STR (though not actually changing the score) which gives me a 10% bonus.

If you choose to interpret the rule that way, it means that a totally average character (10's across the board) would have the same +10% xp bonus as an 18 Str fighter, so you might as well dispense entirely with the clunky concept of a "prime requisite" and simply adjust the xp progression tables so all characters advance 10% quicker. You could explain it to your players as "fighters who aren't very strong/mu's who aren't very smart/clerics who aren't very wise are able to compensate for this deficit by relying on their other attributes."

Personally I have never used prime requisites in my home games. I figure that having a high ability score is its own reward, plus it is less fun for those players who rolled low to continually penalize their PCs throughout their adventuring career for a single bad roll at character generation.

What's most interesting to me is the interaction between prime requisite experience bonus and demihuman level limits. From a certain perspective, playing a high-strength demihuman is less "fun" because you hit your maximum level sooner than your weaker brethren, and there's nowhere to go from there. Hence the popular house rule of granting bonus levels for high prime requisite, or even dispensing with max levels entirely (which is how we play at my house).

[talysman]

Mar 6, 2014 19:03:47 GMT -6 Mushgnome said:

Mar 5, 2014 21:53:34 GMT -6 bestialwarlust said:

So reading through M&M on page 10

"Strength is the prime requisite for fighters. Clerics can use strength on a 3 for 1 basis in their prime requisite area (wisdom), for purposes of gaining experience only. Strength will also aid in opening traps and so on.

Intelligence is the prime requisite for magical types. Both fighters and Clerics can use it in their prime requisite areas (strength and wisdom respectively) on a 2 for 1 basis. Intelligence will also affect referees’ decisions as to whether or not certain action would be taken, and it allows additional languages to be spoken.

Wisdom is the prime requisite for Clerics. It may be used on a 3 for 1 basis by fighters, and on a 2 for 1 basis by Magic-Users, in their respective prime requisite areas. Wisdom rating will act much as does that for intelligence."

People seem to interpret this as reducing one ability to raise another. But reading one can get the impression that you can use the score to determine your experience for prime requisite. So for instance a fighter with a STR of 12 gets no bonus exp. But in reading the above it seems as if you can use Int and Wis to calculate your STR differently. So if my fighter has a STR 12, INT 7, Wis7 I would do the following:

INT 7 (2 for 1) = 3
WIS 7 (3 for 1) =2
Total 5 points

So when calculating experience only I would use the 5 points to my STR and treat it as a 17 STR (though not actually changing the score) which gives me a 10% bonus.

If you choose to interpret the rule that way, it means that a totally average character (10's across the board) would have the same +10% xp bonus as an 18 Str fighter, so you might as well dispense entirely with the clunky concept of a "prime requisite" and simply adjust the xp progression tables so all characters advance 10% quicker.

You're probably going by his original calculations, which he's acknowledged were incorrect. A fighter with Strength, Int, and Wisdom of 10 (the rest don't matter) won't have any experience bonus at all. For a Strength 10 fighter to get the 10% bonus, Int has to be 17+ and Wisdom has to be 18.

This makes me think that one way to simplify the rule would be to define primary, secondary, and tertiary requisites. If the ranges are defined this way:

16-18 Very Hi
13-15 Hi
9-12 Normal
6/7/8 Lo
3/4/5 Very Lo

And if the fighter's secondary requisite is Int and the tertiary is Wisdom... Then you could say the a Hi secondary or Very Hi tertiary would kick the fighter's effective Strength for experience purposes to the next range tier, and a Very Hi secondary would kick it up two tiers. This doesn't always match the by-the-book calculations, but it's close enough, and easier to handle.

(There's also a "co-primary" for thieves, but I haven't worked out a simplification for that one yet...)

Mar 6, 2014 19:03:47 GMT -6 Mushgnome said:

Personally I have never used prime requisites in my home games. I figure that having a high ability score is its own reward, plus it is less fun for those players who rolled low to continually penalize their PCs throughout their adventuring career for a single bad roll at character generation.

If you are using pre-Greyhawk ability score rules, the experience adjustment is the *only* reward for a high Strength or Wisdom score. High Intelligence does give you the extra languages, though. Any other benefits depend on the GM's house rules.

[Porphyre]

In Suppl 1: Greyhawk , it is said that the new exceptional Strength and STR bonus to fighting ability applies only with an unmodified score ("this strength must be raw.i.e. not altered by intellignce scores").
I suppose that this precision implies that Ragnar the fighting-man can have two possible STR scores; the unmodified one, and the modified one. So I would interprete it like Dr Holmes as an actual modification of the ability numbers.

[waysoftheearth]

M&M doesn't say a fighter's intelligence or wisdom scores will adjust his strength score.
It says (on page 10) that a fighter's intelligence and wisdom scores can add to his prime requisite.
This is repeated at the bottom of page 11.

The table on page 11 also illustrates that it is the prime requisite score which determines a PC's experience point bonus/penalty.

Mar 7, 2014 2:33:37 GMT -6 Porphyre said:

In Suppl 1: Greyhawk , it is said that the new exceptional Strength and STR bonus to fighting ability applies only with an unmodified score ("this strength must be raw.i.e. not altered by intellignce scores").
I suppose that this precision implies that Ragnar the fighting-man can have two possible STR scores; the unmodified one, and the modified one. So I would interprete it like Dr Holmes as an actual modification of the ability numbers.

The passage from Greyhawk seems to me to simply restate what is stated in the 3LBBs: the PC's strength score (now especially relevant to a fighter's combat adjustments) is not adjusted by his intelligence score (nor, presumably, by his wisdom score).

I agree that the fighter has two scores here; one being his actual strength score (which is not adjusted by his intelligence or wisdom), and the other being his prime requisite score (which is equal to his strength score adjusted by his intelligence and wisdom scores).

YMMV.

[blackbarn]

After examining this rule again recently I'm a little frustrated. I don't like literally lowering scores to raise another (keeping the scores "pure" feels more honest somehow), but the alternative can get pretty cumbersome. Each way has it's benefits and problems.

I initially thought "for the purposes of gaining experience only" was very clear. But given the vague way these booklets are written, that line could be interpreted as (literally) raising only those abilities (Str, Int, Wis) which can be a factor for purposes of gaining experience.

Dropping the whole thing in favor of straight rolls, period, seems like the fastest, cleanest and easiest method, which feels appropriate for OD&D, so I may go that way. The idea of multiple abilities helping out with XP bonuses is an interesting one, though.

It's a puzzler...

[Stormcrow]

Mar 7, 2014 5:19:11 GMT -6 waysoftheearth said:

M&M doesn't say a fighter's intelligence or wisdom scores will adjust his strength score.
It says (on page 10) that a fighter's intelligence and wisdom scores can add to his prime requisite.
This is repeated at the bottom of page 11.

The interpretation really isn't that clear-cut. Strength is a fighter's prime requisite. It doesn't say anything about "adding" to a score; it says the secondary abilities may be "used" in the prime requisite. The language is not so straightforward as you would have us believe.

[Stormcrow]

There is another interpretation that I recently read that Gary had supposedly confirmed, though I can't find the reference now. Take the explanation quite literally:

"Clerics can use strength on a 3 for 1 basis in their prime requisite area (wisdom), for purposes of gaining experience only." So if a cleric has strength 10 and wisdom 12, their prime requisite is effectively 12 + floor(10/3) = 15, and thus they get +10% to experience.

Going on, we have the following relationships:

Fighter's prime requisite = Str + floor(Int/2) + floor(Wis/3)

Magic-user's prime requisite = Int + floor(Wis/2)

Cleric's prime requisite = Wis + floor(Str/3) + floor(Int/2)

Magic-users really get shafted by this.

The only trouble I have with this interpretation is that just about every character will get the full experience bonus, so what is the point?

[waysoftheearth]

Mar 7, 2014 15:30:49 GMT -6 Stormcrow said:

The interpretation really isn't that clear-cut. Strength is a fighter's prime requisite. It doesn't say anything about "adding" to a score; it says the secondary abilities may be "used" in the prime requisite. The language is not so straightforward as you would have us believe.

The language used in the 3LBBs isn't absolutely unambiguous, but it's not absolutely impenetrable either.

In any event a referee is more or less required to make a clear interpretation--for the purpose of practical gaming--in order to get on with his game.

FWIW, page 11 says: "...may be used to increase prime requisite total...", which looks to me like "adding" to the PR score.

Mar 7, 2014 20:03:51 GMT -6 Stormcrow said:

There is another interpretation that I recently read that Gary had supposedly confirmed, though I can't find the reference now. Take the explanation quite literally:

"Clerics can use strength on a 3 for 1 basis in their prime requisite area (wisdom), for purposes of gaining experience only." So if a cleric has strength 10 and wisdom 12, their prime requisite is effectively 12 + floor(10/3) = 15, and thus they get +10% to experience.

Going on, we have the following relationships:

Fighter's prime requisite = Str + floor(Int/2) + floor(Wis/3)

Magic-user's prime requisite = Int + floor(Wis/2)

Cleric's prime requisite = Wis + floor(Str/3) + floor(Int/2)

Magic-users really get shafted by this.

The only trouble I have with this interpretation is that just about every character will get the full experience bonus, so what is the point?

This is exactly the interpretation I posted above, except that you've omitted the "insofar as this does not bring that category below average" clause.

Which, if added, would make it:

Fighter's prime requisite = Str + floor(max(0, Int-9)/2) + floor(max(0, Wis-9)/3)

Which goes a ways toward addressing your concern.


edit:

M-Us do appear to "miss out" on a possible third contributing factor to their PR, but this would (by the amended function in this post) be at most 3 points--and that only if the tertiary ability score were an 18. In the event that a player rolled an 18 in this other ability, one might wonder if magic-user was the "optimal" class choice?


edit again:

If pressed by an eager player, I'd be inclined to rule dexterity as the M-U's tertiary requisite ability, because the definition of dexterity says "applies to both manual speed and conjuration.". And also--for AD&D--EGG ruled that M-U's should have at least 9 intelligence and at least 6 dexterity.

[Red Baron]

Mar 7, 2014 20:38:49 GMT -6 waysoftheearth said:

If pressed by an eager player, I'd be inclined to rule dexterity as the M-U's tertiary requisite ability, because the definition of dexterity says "applies to both manual speed and conjuration.". And also--for AD&D--EGG ruled that M-U's should have at least 9 intelligence and at least 6 dexterity.

Dexterity, constitution, and charisma already have effects. Only strength, wisdom, and intelligence should then be looked at to determine the prime requisite score.

If you want to boost the magic user's prime requisite, have wisdom also count 1:1 towards it. 

ie. PR = Int + (Wis - 9)

[flightcommander]

I started playing with the Holmes Basic set which, unless I'm mistaken, clearly follows the interpretation whereby prime requisite scores are raised by lowering other attribute scores — a system which is also used in Moldvay Basic. I had frankly never liked this rule all that much because of the way it warps character attributes, so I basically never used it. As a result, I'd never really looked all that closely at the language in OD&D. But after reading this thread, and reviewing my copy, it seems clear (to me) that it was intended that the other attributes contribute, in their measure, to the "prime requisite", without changing the actual attribute scores.

I actually like this ruling a lot, because it doesn't warp character attributes but does provide a bonus to earned experience based on the exceptionality of all three "prime" attributes. I plan to use it this way!

One might argue that magic-users get the shaft; or indeed that only Int and Wis should count, but that's a different flask of worms.

[waysoftheearth]

Mar 7, 2014 21:59:42 GMT -6 Red Baron said:

Mar 7, 2014 20:38:49 GMT -6 waysoftheearth said:

If pressed by an eager player, I'd be inclined to rule dexterity as the M-U's tertiary requisite ability, because the definition of dexterity says "applies to both manual speed and conjuration.". And also--for AD&D--EGG ruled that M-U's should have at least 9 intelligence and at least 6 dexterity.

Dexterity, constitution, and charisma already have effects. Only strength, wisdom, and intelligence should then be looked at to determine the prime requisite score.

I did say "I'd be inclined"; the individual referee can of course rule however he likes.

Worth noting, perhaps, that all the ability scores have a descriptive effect and that can result in a mechanical effect via a character's background and/or what he is purportedly "good at".

High strength implies increasing damage throughout the 3LBBs, and it is extremely common for referees to grant +1 damage to PCs with 15+ strength (as EGG reportedly did), as well as to allow stronger characters to carry more gear/treasure. Moreover, hobbits, children, and other weaklings have less chance to force open stuck doors.

Intelligence and strength jointly determine whether an magic sword will be able to dominate the wielder.

Intelligence grants additional languages (if it is high), determines whether the character is subject to being controlled by telepathy (or similar), and is frequently made to play some part in breadth of spell selection.

Wisdom will act much as does intelligence and, arguably, does everything above that intelligence does if it is the higher of the two abilities.

[Finarvyn]

1. I totally agree with the posters who noted that when you use this rule you have to pay attention to not dropping any stat below average. (This is true no matter which interpretation you make -- actually changing the stat or doing so only for experience purposes.) Otherwise, as has been noted, the numbers moved around are waaaaay too large and the rule becomes pointless.

2. When you introduce the thief, dexterity also becomes a prime requisite stat. It's not unreasonable to assume that dex could be the MU's second stat in the equations noted above.
Magic-user's prime requisite = Int + floor(Wis/2) + floor(Dex/3)

[Stormcrow]

We can state this rule in a more natural way, thus:

The prime requisite of fighting-men is strength, +1 for every two points of intelligence over 8 and +1 for every three points of wisdom over 8.

The prime requisite of magic-users is intelligence, +1 for every two points of wisdom over 8.

The prime requisite of clerics is wisdom, +1 for every three points of strength over 8 and +1 for every two points of intelligence over 8.

Let's try a hopelessly average fighter under this setup: Str 11, Int 10, Wis 10. The total prime requisite score would be 11 + 1 + 0 = 12. This doesn't change earned experience.

Even more interesting is a "useless" fighter: Str 7, Int 12, Wis 12. The total prime requisite score is 7 + 2 + 1 = 10. This moves earned experience from -10% to +0%. This is a viable fighter after all! He relies much more on his intelligence and wisdom than most.

This concept was either dropped or forgotten by the time Greyhawk came out. Thieves have a prime requisite of dexterity, but no mention of secondary or tertiary requisites. In Blackmoor, assassins have three prime requisites, although there is no mention of how to make use of three prime requisites.

Or maybe it wasn't forgotten—maybe thieves have to rely solely on dexterity, and strength, intelligence, and wisdom are pretty much useless to them. I wouldn't do that myself; I'd probably make intelligence a secondary requisite at least (i.e., +1 for every two points over 8).

[Elphilm]

Mar 8, 2014 9:49:05 GMT -6 Stormcrow said:

This concept was either dropped or forgotten by the time Greyhawk came out. Thieves have a prime requisite of dexterity, but no mention of secondary or tertiary requisites.

Hmm? Doesn't page 8 of Greyhawk say: "Thieves use dexterity in the pursuit of their chosen profession. They may use 2 points of intelligence and 1 point of wisdom to increase their raw dexterity score so long as they do not thereby bring the intelligence and wisdom scores below average."

It's another strange formulation; thieves don't actually have a tertiary requisite, just a co-secondary one. You need to have both 2 points of Int and 1 point of Wis to add 1 point to the prime requisite; Int and Wis alone don't do anything, apparently.

[Edit:] Or, thieves actually have two primary requisites, Dex and Wis, and can use Int on a 2 for 1 basis. Ugh.

[Stormcrow]

Thanks, I forgot about that. And again it talks about bringing down scores to raise the prime requisite, not just adding to the prime requisite. Even more: it speaks of increasing the "raw dexterity score," not adding to the prime requisite for calculating the experience adjustment.

In my opinion, the rules are meant to indicate that you actually lower those alternate abilities to raise the ability that is your prime requisite. The bit about "for purposes of gaining experience only" is simply a reinforcement of the fact strength, intelligence, and wisdom have few other listed effects than adjusting earned experience. (Intelligence also gives you extra languages; this may mean that a magic-user who raises his intelligence doesn't get to increase his additional languages.)

[Porphyre]

"Help us Gronan! You're our only hope!"

[oakesspalding]

I go with the view that the swapping is only "virtual". Though it may seem like a funny detail, how one interprets it is relevant to one's entire philosophy of what the class categories and abilities mean.

So, for example, re: Fighting-Men, consider:

1) Actual Swapping.

For Fighting-Men, strength is all that matters. But if you roll up a character with low strength, if you want to play a Fighting-Man, all is not lost. There's a good chance you can trade points from one or two other abilities to increase your strength.

2) Virtual Swapping.

For Fighting-Men, strength is obviously important, but having an above average intelligence and wisdom can also be helpful in how one one learns from and acts on experience, and therefore will also positively affect the rate at which one gets better at fighting.

As a few above have hinted, if you interpret the swapping as virtual, it also helps to make it unlikely that you will end up with a character that has an experience penalty (and unlike the case with actual swapping, you don't have to pay for this by reducing one or two abilities to below average levels), and thus ameliorates the "harshness" of rolling three six-sided dice in order with no mulligans or actual point swapping.

I wrote a few posts on this where I created four charts that made the consequences of the "virtual" interpretation clearer (two years later I used these almost verbatim for Zylarthen), and calculated some odds based on those charts. I hope readers will indulge me to quote my conclusion:

"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?"

[waysoftheearth]

Mar 8, 2014 11:23:39 GMT -6 Elphilm said:

page 8 of Greyhawk say: "Thieves use dexterity in the pursuit of their chosen profession. They may use 2 points of intelligence and 1 point of wisdom to increase their raw dexterity score so long as they do not thereby bring the intelligence and wisdom scores below average."

It's another strange formulation; thieves don't actually have a tertiary requisite, just a co-secondary one. You need to have both 2 points of Int and 1 point of Wis to add 1 point to the prime requisite; Int and Wis alone don't do anything, apparently.

[Edit:] Or, thieves actually have two primary requisites, Dex and Wis, and can use Int on a 2 for 1 basis. Ugh.

Well spotted Elphilm, this seems to me to be the real "edge-case" in this debate.

If I'm reading it right, GH appears to contradict itself in that for fighters it states that adjustments due to "raw" strength are not affected by secondary requisites, while for thieves it states that "raw" dexterity is affected by secondary/tertiary requisites.

One might speculate about whether or not this was intended but, if you intend to use GH, it states clearly that thieves can trade exactly two points of intelligence and one point of wisdom to improve dexterity. Presumably by one point? This trade off could be read as being more limited than the trading noted in M&M, or it could just be more obscurely worded way of saying the same thing.

In my view the notion of an actual ability point trade (where the prime requisite ability score is actually increased, and the other ability scores decreased) doesn't work because the OD&D rules don't cater for ability scores above 18.

A fighter with, say, 17 strength, 13 intelligence, and 12 wisdom would end up with 20 strength. OD&D doesn't cater for 20 strength so it is illogical to make scores of that order possible. A PC with three 18s could in fact achieve 25 strength! That's getting silly even by AD&D standards, and is just nonsense in OD&D.

On the other hand, the rules as written cater perfectly well for a virtual trade (where only the Prime Requisite is adjusted) because the top experience adjustment (+10%) is applicable for PRs of "15 or more".