Why THAC0 Rocks

[TwinBahamut]

It is probably a little late for all of this, but I may as well weigh in my opinion.

My experience with THAC0 is a little unique, simply because I had to actually learn the system because I played in 2E adventures (actually, I DMed them for my brother, with no "experienced player" to tell us how to do things), but I never really immersed myself in those rules for any period of time. It was just me and my brother, having to figure out how the entire system works using a "D&D Adventure Set" with a few adventures and pre-made characters. Shortly afterwards, we acquired real D&D books, which ended up being the first-printed 3E core books. And my first reaction to reading a core rules book for the first time was that the BAB system was a tremendous improvement over THAC0. I didn't even realize that the difference was a result of an edition change, I just liked that it was much easier to use.

THAC0 is really something that you need to immerse yourself in to really "get". With all of these arguments in this thread, there is one question that I have not seen be brought up, which is actually part of my biggest complaint about THAC0. Why, exactly, is the entire thing phrased as your ability to hit AC 0? What is so special about AC 0? When I was actually using the system, I had the hardest time even really grasping what in-character quality THAC0 was even really supposed to represent. The fact that is explicitly references game terminology like numbered AC and dice rolls, rather that character qualities, made it worse.

I mean, it is more than just a difference between adding or subtracting. A "To Hit AC 20" system would possibly be just as confusing as a THAC0 system, even if it used nothing but positive AC values and positive attack modifiers. The problem is the mental task of converting the "To hit AC X" number to the number you need to roll in order to hit an actual AC. It feels like the completely wrong approach, since it feels like someone did work for you, but it was the wrong work, so every actual task involves undoing a step and then redoing it properly.

 

[Thondor]

There were some people who addressed why THAC0 uses the target number of Zero.

It represents a halfway point. In the middle between the greatest AC possible and the worst AC possible. AC 0 is also just about the best AC possible without magical enhancements. (if you have no dexterity bonus you can get AC 2)

Hmmm, I'll have more to comment later.

 

[TwinBahamut]

There were some people who addressed why THAC0 uses the target number of Zero.

It represents a halfway point. In the middle between the greatest AC possible and the worst AC possible. AC 0 is also just about the best AC possible without magical enhancements. (if you have no dexterity bonus you can get AC 2)

Hmmm, I'll have more to comment later.

That misses the entire point. The problem isn't the exact target number, the problem is that the entire system is based around a target number. It is a system in which the math of your basic combat ability is implicit, rather than explicit. It is a system that only works intuitively if you are targeting a foe with AC 0.

Let me phrase this a different way.

In the attack bonus system, the different numbers involves all have direct connections to understandable qualities. Basically, if "luck" (die roll) + "skill" (attack bonus) >= "the enemy's ability to defend itself" (AC), then the hit connects. It is easily intuitive. However, in the THAC0 system, it is closer to "your ability to hit a moderately tough enemy" (THAC0) - "the defense of your current enemy" (AC) = "how lucky you need to be" (target die roll). It is mathematically the same, but it is far more removed from easily understood physical concepts, and thus is harder to use and is less easily remembered.

I'm not sure if I am arguing this perfectly, but there is a conceptual difference that makes the attack bonus system much more intuitive than the THAC0 system. I mean, I am no idiot at math (I am willing to bet that I am well above the average for these boards in terms of mathematical skill), but it took me several hours of practice to understand THAC0 originally (and I still can't remember what you are supposed to subtract from what), but I was able to grasp the attack bonus system instantly.

 

[Remathilis]

There were some people who addressed why THAC0 uses the target number of Zero.

It represents a halfway point. In the middle between the greatest AC possible and the worst AC possible. AC 0 is also just about the best AC possible without magical enhancements. (if you have no dexterity bonus you can get AC 2)

Hmmm, I'll have more to comment later.

So would the system have worked any better/worse with Thac10? (the worst AC)

A 1st level PC (any class) has a thac10 of 10 (must roll a 10 or better on a d20). Each point he rolls higher is a lower AC (11 = 9, - 20 = 0). If he begins to break higher than a 20, he gets negative AC (21 = -1).

Each time he levels (assuming a fighter-type) his thac10 lowers one point.

Mathmatically, it would be the same but you wouldn't have to subtract positive ACs, as you would "starting in the middle"?

 

[HardcoreDandDGirl]

First I have to say at 8 years old (First time playing) I got thac0, by age 10 I could explain it, and figure it without charts or books. And as much as I never failed math, it was far from my best subject in school

So would the system have worked any better/worse with Thac10? (the worst AC)

A 1st level PC (any class) has a thac10 of 10 (must roll a 10 or better on a d20). Each point he rolls higher is a lower AC (11 = 9, - 20 = 0). If he begins to break higher than a 20, he gets negative AC (21 = -1).

Each time he levels (assuming a fighter-type) his thac10 lowers one point.

Mathmatically, it would be the same but you wouldn't have to subtract positive ACs, as you would "starting in the middle"?

Back a few years ago I herd a rumor that TSR had worked on a 3e of there own, like the editions before mostly making optional and common house rules into the book. One thing I herd was that it was Thac10 instead of Thac0.

This same rumor also said that they didn’t have the resources to finish it, and when WotC bought them out, they scraped 85-90% of the work and started almost from scratch on there 3e.

I sometime wonder what that system would have looked like. Your example here now gives me some idea.

does anyone rembere the Mthac0???

 

[Thondor]

So would the system have worked any better/worse with Thac10? (the worst AC)

Well . . . I don't think so.

Something that I think hasn't been addressed so far is that by using the THAC0 system, you deal with fewer large numbers in your math. Which can be nice.

Yes oK THAC0 itself can be a high number, however AC rarely goes above 7 or below -7.

Lets take an example of a 14th level fighter in both systems. No magic weapons, str bonus, or other benefits for simplicity.

Figther has a THAC0 of 6. The DM decides to tell the fighter that his opponent (a Pit Fiend) has a AC of -3.
The player does the math 6 - -3 = 9. He rolls twice for his two attacks. Both are 9 or better! That's two hits!

Fighter has a BAB of +14/+9/+4 . The DM decides to tell the player the opponent (a Hezrou) has a AC of 23.
The player rolls a 6. 6+14 = 20, compares it to the AC not good enough.
The player rolls a 18. He doesn't even bother to do the math, he knows he hits.
the player rolls a 7. 7+4=11 is nowhere near enough.

Sigh, the default presumption in both systems that the DM keeps the AC hidden makes them harder to compare. (default is player does math in BAB and DM does math in THAC0)

I suppose my point is I find it easier to take a Large Static # - A small # <= a Variable # (ThAC0 - AC<= roll) then to take a
Variable # + # or # <= Large static # (roll + 1st BAB or 2nd BAB <= AC)

Aside: really find it difficult to communicate math on the forums.

 

[Moleculo]

Well . . . I don't think so.

Something that I think hasn't been addressed so far is that by using the THAC0 system, you deal with fewer large numbers in your math. Which can be nice.

Yes oK THAC0 itself can be a high number, however AC rarely goes above 7 or below -7.

Lets take an example of a 14th level fighter in both systems. No magic weapons, str bonus, or other benefits for simplicity.

Figther has a THAC0 of 6. The DM decides to tell the fighter that his opponent (a Pit Fiend) has a AC of -3.
The player does the math 6 - -3 = 9. He rolls twice for his two attacks. Both are 9 or better! That's two hits!

Fighter has a BAB of +14/+9/+4 . The DM decides to tell the player the opponent (a Hezrou) has a AC of 23.
The player rolls a 6. 6+14 = 20, compares it to the AC not good enough.
The player rolls a 18. He doesn't even bother to do the math, he knows he hits.
the player rolls a 7. 7+4=11 is nowhere near enough.

Sigh, the default presumption in both systems that the DM keeps the AC hidden makes them harder to compare. (default is player does math in BAB and DM does math in THAC0)

I suppose my point is I find it easier to take a Large Static # - A small # <= a Variable # (ThAC0 - AC<= roll) then to take a
Variable # + # or # <= Large static # (roll + 1st BAB or 2nd BAB <= AC)

Aside: really find it difficult to communicate math on the forums.

Hehe the large numbers argument's a little weak considering that you bring up subtracting negative numbers in your example .

Anyway, I think the beauty of BAB is that it follows the unified D20 mechanic, which is an importance that can't be overlooked. THAC0 was one of the dozens of separate mechanics that the players and DM had to memorize to resolve anything in 2nd Ed.

Even if we were to suppose that THAC0 and BAB were equal, the benefit of having a rule that is internally consistent with the rules as a whole would give the win to BAB. The standardization not only made the combat system make sense, but it contributes to people picking up the game more quickly. I mean why were swords "+1" in 2nd ed? Why weren't they "-1"? They certainly didn't increase your THAC0. Oh so anything that gives me a "plus" to hit, actually decreases my THAC0? Huh?

Secondly, the shift in math can't be ignored. The DM is running the game. In 2nd ed, he had to keep track of the monster's AC, the players THAC0, and the roll the character made. God forbid the characters do anything that affects their bonuses to hit (such as change to their silvered, non-magical sword...)

With BAB the DM just needs to know whether the modified roll is greater than or equal to the AC of the monster. The more work the DM can farm out to the PCs the better. This means the DM can focus on more interesting things that doing math in his head every round.

 

[Jack Colby]

Personally, having played both ways for a number of years, I disagree, for two reasons:

1. Adding is inherently easier than subtracting.

2. Spreading the math from the one DM, who already does way more mental work than the players during the game, to the many players, is easier over the game night.

This. But I wouldn't discredit anyone for preferring THAC0 or feeling it's easier for them. For me, THAC0 is more effort to use, and I have never gotten used to it or liked it. I'll admit there are certain benefits to using it, but I don't mind trading those for easier (for me) calculations and faster, more confident combat actions.

 

[Jack Colby]

Anyway, I think the beauty of BAB is that it follows the unified D20 mechanic, which is an importance that can't be overlooked. THAC0 was one of the dozens of separate mechanics that the players and DM had to memorize to resolve anything in 2nd Ed.

First, memorizing all of those things wasn't necessarily that hard. I managed to do it, and I'm not that bright! Second, the many different subsystems also had at least one advantage over the unified mechanic: it meant they weren't as interwoven mechanically, and a bonus here didn't always affect a score there. In the long run that's a lot less calculating and fiddly bits to worry about during character creation as well as play. They were also more modular, thus, you could houserule/remove, for example, the saving throw system, without it affecting the entire fabric of the game.

Just some thoughts, and I think it reinforces the OPs idea of questioning things that are "obviously" true. There are always going to be people who have another view, and if you listen you might not change your mind, but you will probably learn something.

 

[Thondor]

Hehe the large numbers argument's a little weak considering that you bring up subtracting negative numbers in your example .

First the idea that subtracting a negative number is really difficult is strange. I mean that is like grade four math. All a person needs to realize is that it is actually addition.

The major difference is the number of calculations necessary with BAB.This is especially true for high level:
Usually every single attack, including iteratives require a calculation.
Instead of dealing with 12(roll) + 17(Attack Bonus) every round, plus the iterative attack calculations
You deal with 4(THAC0) - -4 (AC) once. (which is just 4+4) Until your opponent(s) is dropped.
(And yes AC of more then 29 aren't that uncommon in 3rd edition)

With BAB the DM just needs to know whether the modified roll is greater than or equal to the AC of the monster. The more work the DM can farm out to the PCs the better. This means the DM can focus on more interesting things that doing math in his head every round.

At least with THAC0 the DM is really given the option of how he wants to run his game. (and so are the players actually)
1. The players can not know their THAC0
2. The players can know their THAC0 but the DM does the calculations
3. The players do the calculations (they either are told the AC's or calculate what AC they hit).

With BAB your sort of stapled into a one way to do things. Personally I find it quick to either tell the players the AC, or if I want to keep it 'secret' do the calculation myself. In fact its often faster if I just do them myself.