Hating on THAC0

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One of our campaigns is 2E, and switching between that and Next has solidified my distaste for THAC0. We're finally getting faster at calculating, but it's so counter-intuitive to have AC power increasing with lower numbers while ability to defeat AC increases with higher numbers. Is there any rationalization for this system, is it historical, or simply an poor bit of design that hung around for a couple of versions?
It stayed around from 1st edition I think.  Either that or it was just a 2e thing.  2e happens to be a few of my friends and my own favorite edition.  I honestly don't know why people think THAC0 is so difficult.  To be honest when I was a new D&D player, I didn't quite get it at first, but it's just AC-THAC0=the number on die you need to hit.  There are even Character sheets out there on the net that inculde a small section to keep track of your THAC0 and to-hit numbers.  It's realy not that complicated.

I think that " AC power increasing with lower numbers while ability to defeat AC increases with higher numbers " is just a way to try to express that the more training you have (in leveling up) represents a higher ability to-hit (THAC0).  THAC0 snads for To Hit Armor Class 0 (zero) and AC 0 is supposed to represent the lowest an AC can get with armor alone.  So in essence, the way I see it, the two counteract eath other in a way that says, "I've trained long to better myself in combat, and hitting someone in heavy armor is now easier for me."

Armor Classes stay roughly the same in 2e, there are no crazy AC spikes with amazing magic armors or items that give an AC higher than 10 or -10, which I like more than 3.x's AC always climbing higher and higher. So while the enemy has a roughly standard AC, you as a character gain a better chance to hit with levels.  Kinda see what I'm talking about?  The more you level the easier it is for you to hit something.  2e was way different than 3.x's scaling where everything grows in power from everything you do.  I feel like 2e was more constant, where the characters grew according to their own abilities, compared to 3.x and beyond's power creep where everything gets better with leveling and everyone can do everything. 
One of our campaigns is 2E, and switching between that and Next has solidified my distaste for THAC0. We're finally getting faster at calculating, but it's so counter-intuitive to have AC power increasing with lower numbers while ability to defeat AC increases with higher numbers. Is there any rationalization for this system, is it historical, or simply an poor bit of design that hung around for a couple of versions?


You're mixing up the terminology a bit.  What you're hating on is negative integer math, not Thac0 itself which actually deals better with negative integer math.  It's largely just a quirk of fate that the AC values for the earliest editions of D&D descend as the protection improves.  This was simply not much of a problem at the beginnings of D&D as there weren't that many bonuses or penalties to apply to the calculations anyway.  By 1st Edition the actual number needed to hit was being derived from an assortment of attack charts - tables which incorporated a characters class, level, and the AC of the target and provided the base number needed to hit.  One of the features/advantages of those tables was the "repeated 20", which made the best AC's (negative AC's) less "unhittable" by ensuring that a natural 20 would still hit.

Now, in the back of the DMG for 1st Edition there was a listing of all the monsters that had appeared in the Monster Manual a few years earlier.  One of the statistics in that list was a column labled "To Hit AC 0" - T.H.A.C.0.  This was a simple number that performed the function for monsters that the attack tables did for PC's, but without needing to reprint a full attack table.  You could simply take the number indicated for AC 0 and adjust up or down for the actual AC the monster was dealing with.  It was thus a fairly common thing to do for Player Characters as well.  Simply listing THACO values for PC's instead of much larger attack matrices saved space and made it a bit simpler and faster to run the game.  2nd Edition formally did away with all the attack matrices and just used THACO but still retained the same descending AC value scale and the associated negative integer math.  It also did away with the "repeated 20" from the attack matrices making very good AC's more difficult to hit.  However, there still weren't many modifiers that were being piled on to the attack rolls.

By the end of the 2E era it had become a common house rule to convert everthing to ASCENDING AC values and thus finally make combat calculations almost entirely a matter of simple addition.  Again, calculation got a little easier and running the game a bit faster (although you had to keep converting all the printed materials you used to the different AC values).  With 3rd Edtiion the idea of DEscending AC values was forevermore a thing of the past, but also HEAPED piles of bonuses and attack adjustments onto the combat rolls which used up a lot of the advantages of not having descending AC.

Now, if you really want somebody to blame for the "backwards" AC of the early days then if I understand correctly you can blame Dave Arneson.  D&D had initially been using the Chainmail rules written by Gygax and Perren for its combat system, and it was Arneson who took the d20 roll and descending AC from a naval combat game and adapted it for use with D&D.  It was not in the least a bad system at the time because combat was an order of magnitude simpler.  It was only as the game continued to develop over the next twenty years and combat continually became more complicated and detailed that it became a growing issue - not a PROBLEM as such, just something which could stand to be improved and which it would be relatively easy to do - but all the printed materials up to that point would then require adaptation.  The desire to keep 2nd Edition backwardly compatible with 1st Edition was a significant concern at the time.

Still, the math should not be a problematic concept for anyone with math education that involves the concept of negative integers - which includes anyone who gets anywhere near high school algebra.  I watched players who were dumb as rocks come and go in the decades preceeding the arrival of 3rd Edition but none of them had a particular problem with the "backwards" AC and THACO.  Indeed, in my own experience it was players knowing which dice to roll and what bonuses to apply in the first place that was a problem more than being able to do the math.  YMMV.

Old School: It ain't what you play - it's how you play it.

My 1E Project: http://home.earthlink.net/~duanevp/dnd/Building%20D&D/buildingdnd.htm

"Who says I can't?" "The man in the funny hat..."

One of our campaigns is 2E, and switching between that and Next has solidified my distaste for THAC0. We're finally getting faster at calculating, but it's so counter-intuitive to have AC power increasing with lower numbers while ability to defeat AC increases with higher numbers. Is there any rationalization for this system, is it historical, or simply an poor bit of design that hung around for a couple of versions?


You're mixing up the terminology a bit.  What you're hating on is negative integer math, not Thac0 itself which actually deals better with negative integer math.  It's largely just a quirk of fate that the AC values for the earliest editions of D&D descend as the protection improves.  This was simply not much of a problem at the beginnings of D&D as there weren't that many bonuses or penalties to apply to the calculations anyway.  By 1st Edition the actual number needed to hit was being derived from an assortment of attack charts - tables which incorporated a characters class, level, and the AC of the target and provided the base number needed to hit.  One of the features/advantages of those tables was the "repeated 20", which made the best AC's (negative AC's) less "unhittable" by ensuring that a natural 20 would still hit.

Now, in the back of the DMG for 1st Edition there was a listing of all the monsters that had appeared in the Monster Manual a few years earlier.  One of the statistics in that list was a column labled "To Hit AC 0" - T.H.A.C.0.  This was a simple number that performed the function for monsters that the attack tables did for PC's, but without needing to reprint a full attack table.  You could simply take the number indicated for AC 0 and adjust up or down for the actual AC the monster was dealing with.  It was thus a fairly common thing to do for Player Characters as well.  Simply listing THACO values for PC's instead of much larger attack matrices saved space and made it a bit simpler and faster to run the game.  2nd Edition formally did away with all the attack matrices and just used THACO but still retained the same descending AC value scale and the associated negative integer math.  It also did away with the "repeated 20" from the attack matrices making very good AC's more difficult to hit.  However, there still weren't many modifiers that were being piled on to the attack rolls.

By the end of the 2E era it had become a common house rule to convert everthing to ASCENDING AC values and thus finally make combat calculations almost entirely a matter of simple addition.  Again, calculation got a little easier and running the game a bit faster (although you had to keep converting all the printed materials you used to the different AC values).  With 3rd Edtiion the idea of DEscending AC values was forevermore a thing of the past, but also HEAPED piles of bonuses and attack adjustments onto the combat rolls which used up a lot of the advantages of not having descending AC.

Now, if you really want somebody to blame for the "backwards" AC of the early days then if I understand correctly you can blame Dave Arneson.  D&D had initially been using the Chainmail rules written by Gygax and Perren for its combat system, and it was Arneson who took the d20 roll and descending AC from a naval combat game and adapted it for use with D&D.  It was not in the least a bad system at the time because combat was an order of magnitude simpler.  It was only as the game continued to develop over the next twenty years and combat continually became more complicated and detailed that it became a growing issue - not a PROBLEM as such, just something which could stand to be improved and which it would be relatively easy to do - but all the printed materials up to that point would then require adaptation.  The desire to keep 2nd Edition backwardly compatible with 1st Edition was a significant concern at the time.

Still, the math should not be a problematic concept for anyone with math education that involves the concept of negative integers - which includes anyone who gets anywhere near high school algebra.  I watched players who were dumb as rocks come and go in the decades preceeding the arrival of 3rd Edition but none of them had a particular problem with the "backwards" AC and THACO.  Indeed, in my own experience it was players knowing which dice to roll and what bonuses to apply in the first place that was a problem more than being able to do the math.  YMMV.

Dammit, thank you, sir, for explaining this in a more detailed way than I ever have had the patience to do before.  You rule.  Now, instead of taking five minutes to explain why it worked this way, I can just send them this link so I don't have to watch my friends' eyes glaze over as I pontificate and feel uncomfortable going on and on about how long I've played D&D and how old I'm starting to feel. 

Also, I didn't know about Arneson getting that idea from a naval combat game, though I had heard it was him that mainly championed the negative number defense thingy.  Do you know which game that was? 

OD&D, 1E and 2E challenged the player. 3E challenged the character, not the player. Now 4E takes it a step further by challenging a GROUP OF PLAYERS to work together as a TEAM. That's why I love 4E.

"Your ability to summon a horde of celestial superbeings at will is making my ... BMX skills look a bit redundant."

"People treat their lack of imagination as if it's the measure of what's silly. Which is silly." - Noon

"Challenge" is overrated.  "Immersion" is usually just a more pretentious way of saying "having fun playing D&D."

"Falling down is how you grow.  Staying down is how you die.  It's not what happens to you, it's what you do after it happens.”

Also, I didn't know about Arneson getting that idea from a naval combat game, though I had heard it was him that mainly championed the negative number defense thingy.  Do you know which game that was? 

Not even he remembered.  At least I recall that he said he didn't when I attended a little hornblowing session of his at GenCon 2000, which is where I got that particular tidbit.

Old School: It ain't what you play - it's how you play it.

My 1E Project: http://home.earthlink.net/~duanevp/dnd/Building%20D&D/buildingdnd.htm

"Who says I can't?" "The man in the funny hat..."

I actually have nothing but fond memories of thac0.  I was young when 2nd ed. was all there was, and negative ACs were coveted accomplishments.  The math involved was a simple brain exercise for us that we didn't find too annoying.

 Remember the coveted 18/xy strength?  I had a frind roll up a character with 18/96 strength, and he was so happy and proud that he played that character for years.  got him up to lvl 13. 
Is there any rationalization for this system,



No.  It was always a terrible idea.

is it historical, or simply an poor bit of design that hung around for a couple of versions?



Both:  It was a terrible idea that existed in the original game because Gary Gygax was bad at mechanics.  It stuck around for 4+ versions over 20+ years because at first he was a part of them and *never* wanted to admit that any of his bad mechanics were bad, and after he left the idea of changing anything he'd defended for so long was slaughtering a sacred cow.
Confused about Stealth? Think "invisibility" means "take the mini off the board to make people guess?" You need to check out The Rules Of Hidden Club.
Damage types and resistances: A working house rule.
I actually have nothing but fond memories of thac0.  I was young when 2nd ed. was all there was, and negative ACs were coveted accomplishments.  The math involved was a simple brain exercise for us that we didn't find too annoying.

 Remember the coveted 18/xy strength?  I had a frind roll up a character with 18/96 strength, and he was so happy and proud that he played that character for years.  got him up to lvl 13. 



I'm playing Baldur's Gate II and I have no freaking clue what this indicates in the actual game...
Also, I didn't know about Arneson getting that idea from a naval combat game, though I had heard it was him that mainly championed the negative number defense thingy.  Do you know which game that was? 

Not even he remembered.  At least I recall that he said he didn't when I attended a little hornblowing session of his at GenCon 2000, which is where I got that particular tidbit.



And it's not a particularly uncommon mechanic in miniture wargaming.
Infact, you can witness it in action any time you see a game of Warhammer/Warhammer 40k being played.
Ther attacker rolls to hit.  The attacker hits.  Then the defender rolls a d6 & tries to get =/over a target # (found by a combination of armor value, modified by use of shields, barding, cover, & any penalties).  Each bonus drops the # needed.  Each penalty raises it.
Naturally the best #s to start your roll with are the smallest.  So 1 - or less -  is the ideal....
Works well enough in minis gaming.
And D&D grew out of minis gaming....
Thank you for the detailed analysis, and the historical origins. I'll admit that THAC0 math is pretty easy, and of course I greatly desired those negative AC values, but I dislike this exception to "higher is better". Some of our players are new to 2E, and some play in both our 2E and Next campaign, and it slows us down a bit when we get to the one part of either campaign where "lower is better". Am I right about that--is there any other part of either system where that is true? Or 2E DM sometimes has us roll "under our ability score" for an improvised check, but I think he's houseruling that.
People just get stuck in a mode of thinking sometimes.  Even in our 4e games, we still have players who don't know whether you succeed when you match the DC or only when you beat the DC.  I try to get them to think of the DC as a target number and that helps, but I still get people asking all the time if they have to exceed the number or just match it.

OD&D, 1E and 2E challenged the player. 3E challenged the character, not the player. Now 4E takes it a step further by challenging a GROUP OF PLAYERS to work together as a TEAM. That's why I love 4E.

"Your ability to summon a horde of celestial superbeings at will is making my ... BMX skills look a bit redundant."

"People treat their lack of imagination as if it's the measure of what's silly. Which is silly." - Noon

"Challenge" is overrated.  "Immersion" is usually just a more pretentious way of saying "having fun playing D&D."

"Falling down is how you grow.  Staying down is how you die.  It's not what happens to you, it's what you do after it happens.”

People just get stuck in a mode of thinking sometimes.  Even in our 4e games, we still have players who don't know whether you succeed when you match the DC or only when you beat the DC.  I try to get them to think of the DC as a target number and that helps, but I still get people asking all the time if they have to exceed the number or just match it.

Things like this happen because there's no inherently correct way of doing it. It varies from game to game, and I think it might have varied from edition to edition. I call things like this "things to give up explaining." If a player asked me, I'd tell them to rule it the way they think best. It's worth no one's time to quibble over a near miss.

If I have to ask the GM for it, then I don't want it.

Thank you for the detailed analysis, and the historical origins. I'll admit that THAC0 math is pretty easy, and of course I greatly desired those negative AC values, but I dislike this exception to "higher is better". Some of our players are new to 2E, and some play in both our 2E and Next campaign, and it slows us down a bit when we get to the one part of either campaign where "lower is better". Am I right about that--is there any other part of either system where that is true? Or 2E DM sometimes has us roll "under our ability score" for an improvised check, but I think he's houseruling that.


In 2E it was good to roll high for attack and saving throws but low for attribute checks and skill checks.

While it may be easier if it is always better to roll high it is kind of fairer if low rolls can be good sometimes too. Otherwise one may be tempted to find dice that always roll high…Wink

Panartias, ladies-man and Jack of all trades about his professions:

"Once, I was a fighter -

to conquer the heart of a beautiful lady.

Then I became a thief -

- to steal myself a kiss from her lips.

And finally, I became a mage -

- to enchant her face with a smile."

...Otherwise one may be tempted to find dice that always roll high…Wink


Not sure how that would work on a d20, but years ago I met a player who indicated the 'tens' half of his d20 by coloring in randomly triangles. Only on close examination would you see that he had two 20s, two 19s and two 18s.

...Otherwise one may be tempted to find dice that always roll high…Wink


Not sure how that would work on a d20, but years ago I met a player who indicated the 'tens' half of his d20 by coloring in randomly triangles. Only on close examination would you see that he had two 20s, two 19s and two 18s.

Yes, this method used to be quite popular! The good old loaded dice work as well of course and some dice simply have small production-faults so they roll rather high, too.


But in the end all cheating comes down to cheating yourself out of your fun IMO.




Panartias, ladies-man and Jack of all trades about his professions:

"Once, I was a fighter -

to conquer the heart of a beautiful lady.

Then I became a thief -

- to steal myself a kiss from her lips.

And finally, I became a mage -

- to enchant her face with a smile."

He insisted that he only used it as a player when he was truly desparate. At this point he was DM, so I just kept an eye out for that die.
We played 2E for about 6 years every week, with a group of Math, Comp.Sci and Physics students. We never got really used to Thac0. When we finally switched to 3E it was one of the greatest relieves of not having to deal with it any more. (and weapon speeds, combat phases and such).

5e should strongly stay away from "I don't like it, so you can't have it either."

 

I once asked the question (in D&D 3.5) "Does a Druid4/Wizard3/ArcaneHierophant1 have Wildshape?". Jesse Decker and Andy Collins: Yes and the text is clear and can't be interpreted differently. Rich Redman and Ed Stark: No and the text is clear and can't be interpreted differently. Skip Williams: Lol, it's worded ambiguously and entirely not how I intended it. (Cust. Serv. Reference# 050815-000323)

...Otherwise one may be tempted to find dice that always roll high…Wink


Not sure how that would work on a d20, but years ago I met a player who indicated the 'tens' half of his d20 by coloring in randomly triangles. Only on close examination would you see that he had two 20s, two 19s and two 18s.




I haven't checked, but the way my friends roll I think their dice have two 1s
We played 2E for about 6 years every week, with a group of Math, Comp.Sci and Physics students. We never got really used to Thac0. When we finally switched to 3E it was one of the greatest relieves of not having to deal with it any more. (and weapon speeds, combat phases and such).



No matter how easy it can be to understand for some people, clunky is still clunky. Thac0 is a clunky mechanic.

I got started with Palladium, though. Where everything was clunky coated clunky with clunky fillings. The sad thing is, they still haven't updated their rules. Ever. 
Haha, I own a die - I guess you could call it a novelty die - it's shaped like a d20, but it's actually a d10. It has 2 each of the numbers 1 through 10. I told the guys at my table once that I'd give a dollar to the first one to roll an 11 or higher, and they all took a turn (some of them several) before I revealed the trick.

Back to thac0, though... I am reminded of the old tabletop Battletech rules. The distance between the attacker and the target would give you the base to hit target number, as determined on the weapon chart. The greater distance, the higher the target number. Bonuses which made it easier to hit were noted as negative numbers, while penalties which made it more difficult to hit were noted as positive numbers. So for example, at long range (base 8) after running this turn (+2)  firing through 2 spaces of light woods (+1 each) at a target that had moved 6 spaces (+2, as found on a chart) gives a target number of 12. On 2d6.

Anyhow. Back to D&D. I played 2nd edition for years, and it was confusing at first, and even after I'd gotten used to it I would still get mixed up from time to time. I never tried this, but I imagine it'd be pretty easy to convert the negative integers into a more intuitive system. Start by adjusting all the armor classes so that instead of going from 10 (worst) to -10 (best), they go from 10 (worst) to 30 (best). In other words, just use the difference between the AC and 20 and use that as the AC, or, if you prefer, take the difference between the AC and 10, and add it to 10.

For example, an AC of 10 would remain AC 10, an AC 9 becomes 11, an AC 1 becomes 19, an AC -1 becomes 21, and an AC of -10 becomes 30.  

And then, on character sheets and whatnot, just write the AC as adjusted. It wouldn't be necessary to specifically note whether the AC is adjusted or not, because it would be obvious. The only number that is common to both versions 10. That is, if I tell you an enemy has an AC of 8, you know that's not adjusted. If you tell me your AC is 15, that is.

To continue the inversion process, it is necessary to take the difference between the thac0 (as written) and 20, and call that your "to hit" bonus. (Thac0 20 becomes a bonus of 0, thac0 10 becomes bonus of 10, thac0 0 becomes bonus of 20, etc) Same odds at every level, but easier to compute, though it would be somewhat offset by the added complexity of keeping track of "original" vs "adjusted" numbers.  

4 examples:
A 1st level wizard hitting an unarmored peasant-
Old way: subtract AC 10 from thac0 20, need a 10 or higher to hit
My way: add to hit bonus of 0 to die roll, need to roll  10 or higher to hit AC 10

1st level wizard trying to hit heavily armored knight (AC 0)
Old way: subtract AC 0 from thac0 20, need a 20 or higher to hit
My way: add to hit bonus of 0 to die roll, need to roll 20 to hit AC 20

20th level fighter (thac0 of 0, IIRC, and if I'm mistaken please just let it stand for example's sake) attacking an unarmored peasant-
Old way: subtract AC 10 from thac0 0, need a -10 or highter to hit
My way: add to hit bonus of 20 to die roll, need to roll -10 or higher to hit AC 10 

20th level fighter (thac0 0) attacking a magically armored knight (AC -10)
Old way: subtract AC -10 from 0, need a 10 or higher 
My way: add bonus of 20 to die roll, need to roll 10 or higher to hit AC 30 

Hope this helps! I don't think I could explain it any simpler, so if you still don't get it, switch to 3ed Laughing

[Edit: Just went back and re-read The Man In The Funny Hat's wall-o-text and realized most of what I've said here is probably redundant for most players... D'oh! Yell (oh well, I knew it was mostly redundant when I said it in the first place)]
"Can a boat make a hide check?"
I got started with Palladium, though. Where everything was clunky coated clunky with clunky fillings.

Oh, man, you're not kidding.

The sad thing is, they still haven't updated their rules. Ever. 

What, and admit they were wrong?

If I have to ask the GM for it, then I don't want it.

FWIW:  AC was ported to D&D from Chainmail.  It was the number you needed on 2D6 to hit (that number or lower).  AC 10 was the Peasant handed a sharp stick, AC 4 was a Man at arms in Chain with as Sheild

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