Ascending AC Is Superior To Descending AC

Over on Twitter people are bothering to attempt to justify descending AC, as if it ever added anything to the versions of the games that inexplicably implemented it.

In case you haven't played an edition of Dungeons & Dragons prior to 3rd, thousands of years ago during the so-called Advanced age your Armor Class would start at 10, and the more you layered your character in cloth, leather, and/or metal bits the more it would decrease. Even stranger, with a sufficiently high Dexterity (which would apply a negative modifier to your AC), enchanted armor and/or a big enough shield it was possible to knock your AC into the negatives.

While nowadays most editions, derivatives, and vapidware trash hacks use ascending Armor Class (when they use AC at all), where at a glance you know precisely what must be rolled in order to score a hit, back in my day you would roll to hit, the DM asked what your THAC0 was, and then had to do a bit of quick math to figure out if that was good enough.

THAC0 stood for To Hit Armor Class 0. Every class had a THAC0 value, and as you leveled up it would get reduced at varying rates (fighters were the quickest, wizards the slowest). As the acronym implies your THAC0 value was what you had to meet-or-beat on a d20 total in order to hit a target with an Armor Class of 0.

Now where it gets slightly tricky is calculating your to-hit roll for creatures that had positive or negative Armor Class values: if positive you subtracted it from your THAC0, if negative you added it to your THAC0, and this is what you had to roll to hit the target.

For example, if your character has a THAC0 value of 19 and you attempt to strike a creature with an Armor Class of 7, you need to roll a 12 or higher (19 - 7 = 12), and if it has an Armor Class of -1 you instead need to roll a 20 or higher (19 + 1 = 20).

Starting with 3rd Edition THAC0 and descending AC were both wisely abandoned. Armor Class still started at 10, but a high Dexterity (which as one would reasonably expect confers a positive modifier), armor, shields, and other beneficial circumstances caused it to increase. This total value became essentially a target number, so if you attack an enemy with an Armor Class of 15? Whelp, you gotta roll a 15 or higher.

I grew up largely on 2nd Edition, and while I thought it was odd to have a high Dexterity apply a negative modifier to your AC (oddly making it a good thing), for armor and shields to reduce your AC, and for magic armor and shield plusses to likewise reduce your AC it obviously didn't make the game unplayable.

THAC0 wasn't even a particularly impactful hurdle. It was just one of those strange D&Disms that made you wonder why the hell Gary did what he did. You know, like nonsense pseudo-Vancian magic, which s also something I would recommend replacing with something more coherent and compelling (at least flavor-wise).

But at least swapping out nonsense pseudo-Vancian magic would change the game in a meaningful way. Going from descending to ascending AC? It's easy, sensible, and doesn't impact other mechanics. You don't need to playtest anything or worry about adjusting other rules to see if it "breaks" any other part of the game, or at least causes anything to stop working as intended.

This makes it all the more confusing to see a bunch of Twitter-tier strawman-lette arguments attempting to defend it. Here's but a sampler of the disingenuous absurdities:

While it is technically an additional step I've never heard anyone say it's "too hard" or even too many steps. I have no idea how filling a bunch of boxes enhances the game, or is in any way superior or even more intuitive to ascending AC.

I don't think anyone is refraining from playing 2nd Ediiton and prior due to descending AC. I would imagine it has more to do with randomized hit points, reduced impact of ability scores, higher XP requirements per level, level drain, monsters being outright immune to nonmagical weapons, far more lethal poisons and venoms, lack of customization, stuff like that.

I am not saying that I am opposed to those sorts of mechanics which actually have an impact on gameplay, just that I've never heard anyone say that they would totally play 2nd Edition if only it weren't for that dastardly duo that is descending AC and THAC0.

Realizing that descending AC is technically more complex and less intuitive than ascending AC does not mean you're incapable of performing math.

Sure, and then someone figured out that you don't even need to do any of that. Just use ascending AC and treat that as the target number to hit. 

Learned? Perhaps, but not all traditions are worthy of respect. Additionally, unlike side initiative and weapon speed (and a bunch of other mechanics, like weapons versus size categories and spell components), THAC0 and descending AC add nothing to the game.

Again, can't think of anyone saying that it's particularly hard, just unintuitive. This is also a weird way of explaining it: we just added/subtracted the AC from our THAC0 and rolled versus that. 

I agree with the first part of jinx's comment. Ultimately descending and ascending AC will get you where you need to go, it's just that ascending AC is faster and more intuitive. No adding a second mofidifer to another value, no filling in values in boxes.

I think DR is better than AC, because DR makes more sense, but using an AC mechanic technically speeds things up because you don't have to roll to hit, roll damage, reduce damage by one or more DR values, and then apply that to hit points.

That said, where Curator's analogy fails is that changing the game from AC to DR changes other parts of the game: do you increase damage output? Reduce overall hit points? Both? Can you deal 1 damage on a hit no matter what? How does it interact with spells? What do you use to determine if you get hit, instead?

Using ascending AC instead of descending doesn't change any mechanics at all. It's just technically faster and more intuitive.