What does thac0 CONCEPTUALLY represent?

[code9999]

I cannot find anywhere any kind of explanation of the actual conceptual basis for thac0.

What do I mean by conceptual?
If we take a look at the d20 3.5e, AC conceptually represents all the factors that go into how difficult it is to land a damaging blow on a person. Armor can nullify a blow with a weapon (ie the curved design of samurai armor) or make less spots vulnerable to attack, as can magic, while being swift on your feet (dex bonus) can make an opponent hard to hit from dodging all the time, or being really tiny, thus requiring more precision and skill to hit the target.
Or how about the base stats themselves.
Strength conceptually represents physical prowess while dexterity is a person's agility and finesse.
Intelligence is learned knowledge and facts, while wisdom is intuition, "6th sense", street smarts, etc.

So now that you (hopefully) understand what I mean by 'conceptual', what does thac0 conceptually represent?

[JustIgnoreMe]

"How good you are at hitting people."

[The Grue]

Some combination of hand-eye coordination, reflex, intuition and formal weapon training. Being able to strike a target, anticipate how an opponent will respond to your attack, and proper technique in using your weapon to maximize its performance.

[code9999]

Awesome, thanks for the replies guys! I think I can really grasp the concept now.

[veti]

If it's any help, it's pretty much synonymous with 'Attack Bonus' in 3.x.

[JustIgnoreMe]

Weirdly, when I was looking at my 1st Ed core books, I couldn't find THAC0. At all. I found Attack Matrices, but not THAC0. Which was odd.

I know it was used in 2nd Ed, and I think it was used in Red Box D&D, but it seems not 1st Ed.

[spaceLem]

Conceptually it's the difficulty you have in hitting someone with AC 0.

As your THAC0 decreases, so the difficulty you have in hitting AC 0 also decreases.

AC is a modification to the roll. AC>0 is easier to get past than AC 0, so gives you a bonus to hit. AC<0 makes it more difficult.

[veti]

Weirdly, when I was looking at my 1st Ed core books, I couldn't find THAC0. At all. I found Attack Matrices, but not THAC0. Which was odd.

I know it was used in 2nd Ed, and I think it was used in Red Box D&D, but it seems not 1st Ed.

It didn't exist as an explicit concept in 1e. Although I'm pretty sure we did use it, as a shorthand for the attack matrices, before 2e came out - it seemed like a very obvious idea at that point.

[neonchameleon]

THAC0 is just a backwards way of writing BAB - that was a simplification from the Attack Matrices of 1e and earlier that were used because Gygax was using rules stolen from naval combat that didn't expect you to have better than first class armour (i.e. AC1).

[MeeposFire]

Weirdly, when I was looking at my 1st Ed core books, I couldn't find THAC0. At all. I found Attack Matrices, but not THAC0. Which was odd.

I know it was used in 2nd Ed, and I think it was used in Red Box D&D, but it seems not 1st Ed.

The attack matrixes are what they used before THAC0. Essentially the term THAC0 was used to make a shorthand version of the attack matrixes. First it was used as a short hand for monster stat blocks but eventually they realized that using it as a general stat meant you could ditch the list of attack matrixes and just list a number.

THey are the same thing just a shorthand of writing them.

[D+1]

Weirdly, when I was looking at my 1st Ed core books, I couldn't find THAC0. At all. I found Attack Matrices, but not THAC0. Which was odd.

I know it was used in 2nd Ed, and I think it was used in Red Box D&D, but it seems not 1st Ed.
In the appendices of the 1E DMG there's a list of all the monsters from the MM and gives their basic stats. One of the columns in those charts is labeled "To Hit AC 0." I believe it also pops up in monster stats in a module or two, but that's it really. Still, it was and is a common enough house rule in 1E to note "Thac0" rather than have to consult the combat matrix EVERY time.

THey are the same thing just a shorthand of writing them.
Not exactly. When you get to a result of "20" the 1E combat matrices repeat the "20" (a total of six 20's) before continuing progression with 21, 22, etc. That makes it easier in 1E to hit very low AC opponents than in 2E. And it means that at a certain point you tend to need to go back to consult the chart because that gets a little confusing.

[Digitalelf]

It didn't exist as an explicit concept in 1e. Although I'm pretty sure we did use it, as a shorthand for the attack matrices, before 2e came out - it seemed like a very obvious idea at that point.

Actually, it did...

It was first introduced into "official" TSR products as an actual game mechanic in 1983 with the UK modules "UK2: The Sentinel" and "UK3: The Gauntlet". And it later became an "official" part of the rules in 1986 with the publication of the hardbound books: The Dungeoneer's Survival Guide and The Wilderness Survival Guide.

Prior to that, like D+1 said, it was in the back of the 1st edition DMG, where it listed all of the monsters and their other statistics...

[Gaming-Poet]

Since the question has already been answered so thoroughly, I think I can get away with making a personal comment:

I miss THAC0.

If I mention "attack bonus" or "hit points", I could be talking about any number of tabletop or computer games.

If I mention "armor class", I'm probably talking about Dungeons & Dragons, but which edition?

But all I have to do is cry out at a convention "THAC0!", and there is no question what I'm talking about, and there's no question that the ones who joyously echo my cry are all fellow AD&D fans.

How many games have that sort of terminology impact?

[Siosilvar]

Not exactly. When you get to a result of "20" the 1E combat matrices repeat the "20" (a total of six 20's) before continuing progression with 21, 22, etc. That makes it easier in 1E to hit very low AC opponents than in 2E. And it means that at a certain point you tend to need to go back to consult the chart because that gets a little confusing.

IIRC they had o be natural 20s. Which got simplified into "natural 20 is an auto-hit" for simplicity instead of something weird that works sort of like "natural 20 counts as 25" except not quite.

[Philistine]

Since the question has already been answered so thoroughly, I think I can get away with making a personal comment:

I miss THAC0.

If I mention "attack bonus" or "hit points", I could be talking about any number of tabletop or computer games.

If I mention "armor class", I'm probably talking about Dungeons & Dragons, but which edition?

But all I have to do is cry out at a convention "THAC0!", and there is no question what I'm talking about, and there's no question that the ones who joyously echo my cry are all fellow AD&D fans.

How many games have that sort of terminology impact?
I think you're conflating "distinctiveness" with "importance." Surely the fact that nobody copied THAC0 - not even later editions of D&D! - actually speaks to how limited its impact was, don't you think? "Armor Class" and "Hit Points" were widely copied; they helped shape the landscape and working vocabulary of RPGs. The primary contribution of "THAC0" to the modern gaming vocabulary is as an example of what to avoid.

[Digitalelf]

The primary contribution of "THAC0" to the modern gaming vocabulary is as an example of what to avoid.

Obviously, I'm not Gaming-Poet, but non-the-less, I'd like to address this portion of your post...

I don't think it was THAC0 that later editions were avoiding, I think that if anything was "avoided" in later editions, it was descending armor class; I mean, THAC0 was actually brought forward from 1st edition, which, IMHO, was a VAST improvement over all of those to-hit tables in the DMG used during 1st edition's beginnings.

[Philistine]

That's another thing modern games avoid. While it's a related issue, the two are nevertheless separate.

THAC0 specifically rates a character's martial prowess in terms of "odds of making a successful attack against a standard, but somewhat arbitrary, defensive value." There's nothing remotely equivalent to that in later editions of D&D - if it was just a matter of switching from decreasing AC to increasing AC, 3E ought to have a term like "THAC20." There is no such term, because (it turns out) keeping track of a character's "Attack Bonus" and comparing it to the actual defense score of each opponent is much, much simpler, conceptually, than keeping track of a character's "Odds of Hitting a Specific Defensive Value" and then recalculating the probability of hitting every time the character faces a new opponent, based on the opponent's actual defense score. Even systems where it could make sense to have a similar stat (Savage Worlds comes to mind, with a standardized "Target Number" of 4 for most checks - including combat - but with modifications possible to both the roll and to the TN) don't have an equivalent to THAC0. For what it's worth, I agree that THAC0 is less clunky than looking up the results of every individual die roll on a To-Hit Table. That doesn't make THAC0 not clunky.

Anyway, the point is that games since AD&D haven't used the term "THAC0" (if they had, you couldn't spot the AD&D fans at a con just by yelling "THAC0!"), which in fact indicates it's had a very limited impact on game terminology.

[obryn]

Since the question has already been answered so thoroughly, I think I can get away with making a personal comment:

I miss THAC0.

If I mention "attack bonus" or "hit points", I could be talking about any number of tabletop or computer games.

If I mention "armor class", I'm probably talking about Dungeons & Dragons, but which edition?

But all I have to do is cry out at a convention "THAC0!", and there is no question what I'm talking about, and there's no question that the ones who joyously echo my cry are all fellow AD&D fans.

How many games have that sort of terminology impact?
I really, really don't miss THAC0 and I've been playing since 1982 or so.

While there's benefits to the general structure of a system which bounds AC between -10 and 10, and benefits to the way attack bonuses scale in AD&D, THAC0 itself is unwieldy.

Yes, plenty of people can do it in their heads. Plenty of people are experts at it. Plenty of people will tell you it's not that hard. Which is all kind of true, but the big problem with THAC0 is the problem of subtraction, and further the subtraction of negative numbers. Subtraction should be avoided, when possible, because it's not commutative... 3+5 = 5+3, but 3-5 =/= 5-3. This means players need to remember the order of operations while playing, and it's additional cognitive overhead.

THAC0 was invented to serve as a mathematical shorthand for what was a clunky system to start with. It was invented to solve a specific problem ("I don't want to print a whole attack matrix here") but there's much more elegant solutions out there. When playing oldschool games, I much prefer the "Target 20" mechanic, for one example.


I think you're conflating "distinctiveness" with "importance." Surely the fact that nobody copied THAC0 - not even later editions of D&D! - actually speaks to how limited its impact was, don't you think? "Armor Class" and "Hit Points" were widely copied; they helped shape the landscape and working vocabulary of RPGs. The primary contribution of "THAC0" to the modern gaming vocabulary is as an example of what to avoid.
Yep. If nobody had ever invented THAC0, the RPG world wouldn't be any worse off (or incredibly different) right now. It's a bit of technology that's fallen by the wayside, like 8-tracks and laserdiscs.