Let's Talk About THAC0

Oofta

Title? I don't need no stinkin' title.
Well, 5e went to bounded accuracy in large part because of the huge numbers bloat of previous editions. A much needed design change. But given a choice between 2e's THAC0 and 3e's ascending system, 2e all the way. Even with doing subtraction, it was way easier and faster. You didn't sit there adding a half dozen modifiers that constantly changed depending on what was going on just to figure out what AC you hit.
I'm not saying 3.x didn't have issues. Or any edition for that matter. Just that you're conflating having half a dozen modifiers with the move away from THAC0 (which by the way is pronounce THACK-OH and everybody else is just saying it wrong :p ). They're different topic.

Of course I didn't have a problem with 3.x either, although it did get a bit crazy when I had to have a grid with all possible modifiers and had to roll double handfuls of dice to resolve my full attacks. Then again that was partly my fault for having a dual-wielding fighter with multiple energy types on my weapons in a party that liked to buff the snot out of him. Good thing I quit playing 3.x before I got my dual-wielding beastmaster(?) to a higher level because I would have needed a bigger dice bag for the mount's attacks. Ah fun times rolling dozens of dice.
 

Sacrosanct

Legend
(which by the way is pronounce THACK-OH and everybody else is just saying it wrong :p ). They're different topic.
.
Yeah, I was wondering what was going on upthread. I was like, "There IS an H in there...". We always pronounced it THACK OH.
 

Oofta

Title? I don't need no stinkin' title.
I was just staying quiet on this one, but we always went with THAKE (like lake) -OH. XD
Maybe we should have a poll "how do you pronounce THAC0". Of course you would only need two options, "THACK-OH" and "The wrong way". ;)

Kidding aside, I never met anyone who didn't pronounce it THACK-OH. Maybe it's a midwestern thing.
 
Addition is easier than subtraction.

Also, the title made me think:
Let's talk about THAC0 baby
Let's talk about you and me


P.S. It's pronounced "thar-koh" because armor class. Duh.
 

Xaelvaen

Explorer
Maybe we should have a poll "how do you pronounce THAC0". Of course you would only need two options, "THACK-OH" and "The wrong way". ;)

Kidding aside, I never met anyone who didn't pronounce it THACK-OH. Maybe it's a midwestern thing.
Quite possibly - Southeast U.S. here. I believe we went long A because of the acronym AC having a long A. It's all good!
 

Mort

Community Supporter
My friends and I wandered around Gen Con in "I remember THAC0" t-shirts.

We heard a rumor that There was someone wandering the convention in a red hat with "Make THAC0 great again" but, sadly, we couldn't find him for a photo op!

THAC0.jpg
 

billd91

Hobbit on Quest
I feel sorry for poor old THAC0. It has a bad reputation for being complex, when it's exactly as complex as the current method!
Algebraically, maybe not. But from a practical perspective, it is more difficult because there are always going to be people having more difficulty with negative numbers than dealing entirely with positive numbers. It has a bad reputation, compared to turning the AC values around in 3e, because it served as a barrier to people understanding and using it.

From a usability perspective, there is no question that rising ACs is a better mechanic.
 

MonkeezOnFire

Adventurer
The math may be as simple but it is less intuitive as a mental model. Larger numbers usually means more of something. So having lower AC represent having more armour is counter intuitive. It also creates confusion when these models are inconsistent across mechanics. "You mean I want my strength score to be high, but my AC should be low?"
 

akr71

Explorer
Yeah, I was wondering what was going on upthread. I was like, "There IS an H in there...". We always pronounced it THACK OH.
Thack Oh here too. I believe those pronouncing it Tak- are francophone and a TH makes an (english) T sound in french.
 

lowkey13

I'm sorry, Dave. I'm afraid I can't do that.
Thack Oh here too. I believe those pronouncing it Tak- are francophone and a TH makes an (english) T sound in french.
Maybe they just really, really like tacos?

Or maybe, just maybe, they play OSR on only one day of the week?


"Hey, everybody, y'all ready for THAC0 Tuesday?"
 

Umbran

Mod Squad
Staff member
I feel like THAC0 gets a bad rap. It's the precursor to 3E's Base Attack Bonus, and came after 1E's attack matrices. It's actually super simple.

The important thing to remember is that it's the exact same math, but in reverse.

In 3E-5E, you roll d20 and add a bonus in order to beat the target's AC.

In 1E-2E, you roll d20 in order to beat THAC0 minus AC.​

So instead of adding a number to your d20, you simply deduct a number from your THAC0. Same maths, just minus instead of plus.
This is less a mechanical issue, and more a "user experience" issue, but it does matter.

If you are a computer, there's no real difference. However, for real-life humans, addition is easier than subtraction. If you give folks a set of simple additions to do, and a set of similarly simple subtractions, the subtractions will take notably longer.

Since subtraction has a measurably higher cognitive load, though they are mathematically equivalent, THAC0 actually makes people pause longer to figure out what they need to roll, and it breaks immersion more.
 

Morrus

Well, that was fun
Staff member
I hope another dozen people explain to me that addition is easier than subtraction! :)

Nevertheless, I still maintain my position that THAC0 is not as complex as it’s reputation would lead you to believe, whether or not addition is easier than subtraction.
 

Blue

Ravenous Bugblatter Beast of Traal
Mathematically, people do addition faster than subtraction. d20+bonus >= target is super quick at the table. The addition is quick, the comparison to target is quick. Subtraction or table lookup is slower.

Also, d20+bonus >= target is quite intuitively obvious. Especially among new players the chance of success (knowing bonus and target) is clearer without working it out.

THACO doesn't seem to bring any advantages to offset either of these, much less both.
 
I'm not saying 3.x didn't have issues. Or any edition for that matter. Just that you're conflating having half a dozen modifiers with the move away from THAC0
To be fair, the move away from THAC0 with 3e was at least /correlated/ with having more than half a dozen modifiers. There were, what? 17 named bonus types in 3e? (Google seems to think it was 18...)
And untyped bonuses could stack with those, and eachother.

Not that typed bonuses are all bad. In 3e, avoiding anything stacking with armor was a simple matter of giving it an Armor Bonus. In the name of simplicity (actually, natural language) 5e does not use named bonuses. But, it still wants some things to not stack with armor, which has slightly confused people, prompting this 1700 word article (that I stumbled about while googling those bonus names from 3), to accomplish what the two words "armor bonus" did in 3e. ;)

http://dmsworkshop.com/2017/05/19/things-you-didnt-know-about-dd-5e-calculating-ac/



I feel like THAC0 gets a bad rap. It's the precursor to 3E's Base Attack Bonus, and came after 1E's attack matrices.
It couldn't help but be briefer in presentation than the two facing pages of attack matrices in the 1e DMG. But the matrices weren't complicated, a table lookup is really pretty simple.

And, THAC0 lost one feature of those matrices: When you had /very/ low (good) ACs, '20' would appear on the table multiple times. The first time, you needed a total of 20, thereafter a natural 20. When you finally got to 21+, you needed a natural 20, and a net bonus. It was a more nuanced progression than 'natural 20s always hit.'

It's actually super simple.
....I feel sorry for poor old THAC0. It has a bad reputation for being complex, when it's exactly as complex as the current method!
A sub-system can be simple, but add to complexity, because it's different for no reason and to no benefit.

d20 consolidated sub-systems that used d%, d6, d20 roll-under, and d20 roll-high (among others) into d20 + mods vs DC. That was a simplification.

THAC0 definitely belonged on the chopping block because it accomplished the same thing as rolling high to hit an AC - a pass/fail roll on a d20, giving a % chance of success with a granularity of 5% - but did it differently, as you explained:
The important thing to remember is that it's the exact same math, but in reverse.

In 3E-5E, you roll d20 and add a bonus in order to beat the target's AC.

In 1E-2E, you roll d20 in order to beat THAC0 minus AC.

So instead of adding a number to your d20, you simply deduct a number from your THAC0. Same maths, just minus instead of plus.
Same maths, two different ways to do them = needless complexity.

The same goes for saving throws vs attack spells. There's no mathematical difference between a caster rolling an attack and his target rolling a save - the distinction is just needless complexity.
 
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Jer

Adventurer
The important thing to remember is that it's the exact same math, but in reverse.

In 3E-5E, you roll d20 and add a bonus in order to beat the target's AC.

In 1E-2E, you roll d20 in order to beat THAC0 minus AC.​
I think the arguments about subtraction and negative numbers being a bit more difficult for folks to grasp have some merit - especially among the folks who were interested in the game but were not mathematically inclined (which is part of the reason I think Vampire took off the way it did - you didn't need to do any addition or subtraction, just counting dice over a threshold).

But in addition, a stumbling block that I remember from D&D and bringing new people on board was the inconsistencies on the character sheet and at the table. Sometimes lower numbers were better, sometimes higher numbers were better. When you leveled up some things went up (like hp and thief skills) and some things went down (like saving throws and THAC0). Sometimes beneficial magic items gave you a bonus as a positive number (+1 to hit), sometimes the bonus was negative (-1 to AC). Sometimes you were trying to roll over a number (to hit, saves) and sometimes roll under (thief skills, or ability checks for those of us who used them). And it's another reason that I think Vampire took off and opened things up to a wider audience - yeah it had a lot of quirks, but the die rolling was always a consistent mechanic and as a new player you didn't end up feeling stupid for not remembering the quirks of whichever subsystem you were using for a particular check.

ETA: And while I was composing this, Tony Vargas made a similar observation - ninja'd!
 
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vincegetorix

Jewel of the North
We always pronounced it “tako” as opposed to “tak zero”, and used masculine pronouns. That seemed pretty universal in my groups from the Laurentians to Montreal to Sherbrooke here in Quebec. Never played in the Quebec city area however.
I'm also in the ''le tako'' camp and I'm in Québec City, but I had players from the south side of the river (Levis, Kamouraska and Beauce refer to it as ''la Tak-zero''. Strange people on the south side...strange people...

:p

Anyway, thanks all for your answers, you may ignore my thread derail.
 

Dausuul

Legend
Nevertheless, I still maintain my position that THAC0 is not as complex as it’s reputation would lead you to believe, whether or not addition is easier than subtraction.
I'm not sure THAC0 has a reputation at all, if by "reputation" you mean "opinion held by people without direct knowledge." In my experience, people either know what THAC0 is because they played 2E, or they didn't play 2E and have never heard of it.
 

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