Let's Talk About THAC0

Retreater · Jun 8, 2019

In the day we called it "THACK - oh" though I've now started pronouncing it "THAY-koh."

And even though I was with AD&D 2nd edition since about the start of that edition, the concept of THAC0 was a major stumbling block and not intuitive. I'm glad it's gone, and if I were to run 2e again, I would convert to modern ascending AC and attack bonuses.

Lanefan · Jun 8, 2019

digitalelf said:
THAC0 was first introduced to AD&D (1st Edition) as a usable game mechanic in 1983 with the module "UK3: The Sentinel" as an optional rule.

It latter appeared as an "official" part of the 1st edition ruleset in 1986 with the publication of the "Dungeoneer's Survival Guide" hardbound.

I could be wrong, but I'm fairly sure THAC0 was kicking around in Basic before this - which probably explains some of the confusion, as many of us kinda lumped Basic and AD&D together at the time mostly by using Basic modules in AD&D games.

However, that said, neither the Combat Matrices nor THAC0 keep the player from determining the AC of any opponent they face.

The way you do it, the player can easily determine the AC of their opponent by the process of elimination... "Well, a 14 did not hit, but a 15 does, so that orc's AC must be at least 3".

This, however, I don't mind - it reflects the warrior learning more about the foe she's facing as the combat goes on. And there's still some guesswork involved - OK a 14 misses and a 15 hits, but if I don't know my combat-matrix position (a.k.a. BAB) I don't know how much of my success is coming from that vs. how much is related to the foe's AC.

Beleriphon · Jun 8, 2019

vincegetorix said:
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 . 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

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.

On French, THAC0 is an acryonym of To-Hit Armour Class 0; so I'd go with whatever gendered pronoun you'd use for Armour Class in French.

As for the math, its very clearly: (Die roll + Modifiers) - THAC0 score = AC Hit

Thus, a roll of (13 + 2 for a magic weapon) - THAC0 18 = 3, so we hit AC of 3.

The issue is that in the AD&D rules at any point actually explain the process of attacking in that way. So the process isn't hard at all, its not really that much harder than d20 roll + BAB + Mods = AC. The difference is that the rules in 3E explain this all very clearly in the rules dealing with attacks.

The other big difference is that AD&D had a bunch of disparate subsystems that didn't really add up the same since some were roll under with modifiers to die rolls, others were roll over with modifiers to die rolls, some were roll under with modifiers to target numbers.

On the last one look at saving throws. A bonus from some kind of item was say +2 to Save vs Wands. That's actually a bonus to the score, so if your character had a score of 16in that save category, while wearing the magic item it became 18, which only fails on a 19 or 20, rather than a 17 through 20.

The biggest change 3E did was consolidate the way rolls were made to begin with. THAC0 is easy enough, but there is no reason it should be a completely different set of math for task resolution from every other task resolution in the game. So it should either all work like THAC0, or should all work like something else, but having a dozen different methods to calculate success from rolling a d20 is why THAC0 has a bad reputation, its the poster child for mismatched task resolutions.

Oofta · Jun 8, 2019

Morrus said:
Wow?

So ... you don't accept that some people found THAC0 painful? You keep asking people to explain it to you. It's simple. Some people find it more difficult. Period. End of story.

You ask "why" ... well the answer is that apparently not everyone thinks like you do. My wife started playing D&D with 2E and she hates THAC0 because it makes her subtract and she finds the numbers (especially negatives) confusing. She's a lot smarter than me (and most people for that matter) in a lot of ways, but she would never go back to 2E because of the "backwards math".

I can't give you a better explanation, nobody can. Some people find it more difficult and greatly prefer the way the rules changed for 3. That's either something you can accept or not.

Morrus · Jun 8, 2019

Oofta said:
So ... you don't accept that some people found THAC0 painful? You keep asking people to explain it to you. It's simple. Some people find it more difficult. Period. End of story.

Woosh.

It’s a joke.

Staffan · Jun 9, 2019

Tony Vargas said:
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.

Except that the difference creates real differences in who's "responsible" for the event and who has the power to affect it. For example, if a character has Inspiration in 5e they can use it to get advantage on an attack roll, but they can't use it to give their opponent disadvantage on their save.

Tony Vargas · Jun 9, 2019

Staffan said:
Except that the difference creates real differences in who's "responsible" for the event and who has the power to affect it. For example, if a character has Inspiration in 5e they can use it to get advantage on an attack roll, but they can't use it to give their opponent disadvantage on their save.

Sure, that difference is a system artifact.
Conceptually, the attacker is always responsible for the event. He attacked, whether with weapon, cantrip, spell, or quip.

And, both attacker and defender (If not helpless) should, conceptually, be able to affect the outcome.

Beleriphon · Jun 9, 2019

Tony Vargas said:
Sure, that difference is a system artifact.
Conceptually, the attacker is always responsible for the event. He attacked, whether with weapon, cantrip, spell, or quip.

And, both attacker and defender (If not helpless) should, conceptually, be able to affect the outcome.

Star Wars SAGA Edition did this. Everything is an attack, it just depends on what number as the attacker you need to use to be successful. So a grenade is an area attack against the defenders relevant defense scores.

billd91 · Jun 10, 2019

Beleriphon said:
Star Wars SAGA Edition did this. Everything is an attack, it just depends on what number as the attacker you need to use to be successful. So a grenade is an area attack against the defenders relevant defense scores.

Yeah, but it kept the PCs from using their Force points to defend themselves because they could no longer use one to gain a bonus on their saves. In the end, it felt like a net loss for the system, particularly with respect to the setting and the heroic/Jedi ethos of using the Force for defense in preference to attack.

Tony Vargas · Jun 10, 2019

billd91 said:
Yeah, but it kept the PCs from using their Force points to defend themselves because they could no longer use one to gain a bonus on their saves.

Could they use it for a bonus to AC, before, too? Seems like Jedi do a lot of dodging and blocking.