Let's Talk About THAC0

Morrus

Well, that was fun
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.

If your THAC0 is 15, and your target's AC is 2, you need to roll 13. It's that simple! (Remember, lower AC was better).

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!
 
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lowkey13

I'm sorry, Dave. I'm afraid I can't do that.
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!
The following observations are inarguable, as they are the result of maths and/or tables:

1. THAC0 is clearly superior.

2. However, it is only superior to the extent that it is derived from the ur-superior system, tables of attack matrices.

3. Tables > everything else.

4. In addition, armor classes should go down (lower IS better), in the way that God and Gygax intended.

5. -10 is something to be eternally lusted after, is it not? Is there no place in modern Dungeons and Dragons for negative numbers?????? We must no longer cater to the tyranny of the innumerate.

6. Finally, THAC0 is just fun to say. SAY IT! SAY IT NOW!

I rest by case, which is both indisputable, and indubitable.

You're welcome.
 

vincegetorix

Jewel of the North
A question for older players and/or english speaker:
Do you ponounce THACO as ''tak-zero'' or ''tako''? Me players and myself are all under 30 (never used THACO in any games beyond BG1-2) and french speakers and I've seen both ways. So which is the right way (as Gygax and God intended, as someone would say :p )?
 

Morrus

Well, that was fun
Staff member
A question for older players and/or english speaker:
Do you ponounce THACO as ''tak-zero'' or ''tako''? Me players and myself are all under 30 (never used THACO in any games beyond BG1-2) and french speakers and I've seen both ways. So which is the right way (as Gygax and God intended, as someone would say :p )?
The latter. The former sounds like too much work!

Thackoh.
 

Xaelvaen

Explorer
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!
About two years ago, a group of people at my FLGS got into a conversation about Dungeons and Dragons, and I brought up 2E, how I started, and the nostalgic feel of it. By the end of the evening, they had decided they wanted to try 2E with me. Two weeks later, I bring all my gloriously old books, help them spend hours on character creation with all my favorite options extra material.

Next week, play begins, and we go over some introductory things - like you've mentioned, thac0 (negative armor class, and more). I ended up printing out the d20 sheets for them - 20 blocks labeled 1 - 20. After adjusting for thac0, in each block you write what AC your roll would hit. So we start playing - rolls hit the table, they compare to their little charts 'That'd hit AC -3!' and so forth.

They never once complained of complexity, really dug the character customization and 'old magic' feel of the world. It probably didn't hurt we played with my old Faerun box set too, so even the world matched the system well. Ended up playing for about 6 months. Thac0 does get a bad rap, but there are some magic tricks to make it even simpler.
 

vincegetorix

Jewel of the North
The latter. The former sounds like too much work!

Thackoh.
Ha, that was my understanding.

Follow up question: Would ''THACO'' be a feminine or masculine word? Believe it or not, this as been the subject of many friendly debate at my table :p . For those who speak french, would it be ''le THACO'' or ''la THACO''? There's unfortunately no true neutral in french.

Thanks for your time, this thread will help me assert my DM domination over my table :p

As for the mechanic itself, once it is explained like this its indeed quite easy, I dont know why I thought it was way more obscure than that.
 

Morrus

Well, that was fun
Staff member
Follow up question: Would ''THACO'' be a feminine or masculine word? Believe it or not, this as been the subject of many friendly debate at my table :p . For those who speak french, would it be ''le THACO'' or ''la THACO''? There's unfortunately no true neutral in french.
I woudn't know. I'm not French. You decide! :)
 

Xaelvaen

Explorer
Ha, that was my understanding.

Follow up question: Would ''THACO'' be a feminine or masculine word? Believe it or not, this as been the subject of many friendly debate at my table :p . For those who speak french, would it be ''le THACO'' or ''la THACO''? There's unfortunately no true neutral in french.

Thanks for your time, this thread will help me assert my DM domination over my table :p

As for the mechanic itself, once it is explained like this its indeed quite easy, I dont know why I thought it was way more obscure than that.
I suppose a neutral approach would be 'Le', since Gygax is the foundation of Dungeons and Dragons, he and Arneson are both male.
 

Sacrosanct

Legend
The common argument is that adding is inherently easier than subtracting. Which is true, I suppose, but it's so minor I can't see the difference. 2+2 is just as easy as 4-2. I recall an interview Skip Williams did re: 2e and ascending AC. He said, "Of course we thought about ascending AC at the time we were designing 2e, but we wanted players to be able to use their 1e stuff with the 2e system." I think they made the right choice.
 

Oofta

Title? I don't need no stinkin' title.
All I can say is that for some people, THAC0 was a stumbling block. It never really bothered me but it is easier to add than subtract, especially into the negatives. But some people have enough problems adding two simple integers. I don't see how it could really affect the end result all that much but "high is always better" and one concept for attacks/saves/checks streamlines things.

In other words, I've never seen any advantage to THAC0 other than nostalgia. It worked in it's day but I'm glad it was replaced.
 

Sacrosanct

Legend
In other words, I've never seen any advantage to THAC0 other than nostalgia. It worked in it's day but I'm glad it was replaced.

It capped max AC at -10 (which you hardly ever got that low anyway). That's a huge advantage over the incredible numbers bloat of 3e, where ACs could go into the 40s and higher.
 

Morrus

Well, that was fun
Staff member
In other words, I've never seen any advantage to THAC0 other than nostalgia.
It's not that it had more value than the current one. Nobody's claimed that. It's just that it's not as complex as it has a reputation for. That's all. :)
 

Oofta

Title? I don't need no stinkin' title.
It capped max AC at -10 (which you hardly ever got that low anyway). That's a huge advantage over the incredible numbers bloat of 3e, where ACs could go into the 40s and higher.
Numbers got crazy in 3/4, but I've never seen an AC of 30 in 5E. They could exist in theory but it would be easy enough to just set a max AC of whatever you want. I don't see any link between THAC0 and limiting AC to a reasonable number.

Whether we should limit AC to some number (20, 30, sky's the limit?) is a separate topic.
 

Oofta

Title? I don't need no stinkin' title.
It's not that it had more value than the current one. Nobody's claimed that. It's just that it's not as complex as it has a reputation for. That's all. :)
I'm just relating, like, my experience man. :cool:

Several people I played with were relieved when we switched to 3 that they no longer had to do what they considered "backwards math". Maybe you and people you played it didn't think it was bad because it was a self-selecting group. Personally I didn't hate THAC0, but I wasn't fond of it either. D&D has enough idiosyncrasies and sacred cows I'm glad some were turned into rule-burgers along the way.
 

jasper

Rotten DM
What was the problem? Did your momma only allow you to sharpen your pencil once a month.
You found your Thaco. Then wrote 10, 9 ,8 etc etc to -10 on the bottom of your notebook paper. And below that you wrote the number. Easy. Or you could do a column thaco 15
10 - 5
9-6
etc
etc
0 - 15
-1-16
etc
etc
-10 - 25.
easy as pie.
 

Laurefindel

Explorer
A question for older players and/or english speaker:
Do you ponounce THACO as ''tak-zero'' or ''tako''? Me players and myself are all under 30 (never used THACO in any games beyond BG1-2) and french speakers and I've seen both ways. So which is the right way (as Gygax and God intended, as someone would say :p )?
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.
 
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Sacrosanct

Legend
Numbers got crazy in 3/4, but I've never seen an AC of 30 in 5E. They could exist in theory but it would be easy enough to just set a max AC of whatever you want. I don't see any link between THAC0 and limiting AC to a reasonable number.

Whether we should limit AC to some number (20, 30, sky's the limit?) is a separate topic.
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.
 

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