Quote Originally Posted by Premier View Post
It's really simple.
Also, regarding the ubiquitous "It's unintuitive!" complaint: No it isn't. You're misusing the word. "Unintuitive" would mean that humans are inherently built to equate "higher number" with "better quality". However, this is plain simply not true. 1 is a lower number than 2, and yet, nobody ever says that "1st class train tickets being better than 2nd class ones is unintuitive!" Nobody ever whines "Why do they call excellent actors (or any other professionals) "1st rate" and bad ones "3rd rate"? Higher numbers should mean better! It doesn't make sense!" A Petty Officer 4th Class and a Petty Officer 2nd Class on a Navy ship never get confused about who's superiour to whom. Heck, even spaceships are launched on a countdown, not on a countup from zero to ten, and nobody ever criticizes the technique on grounds of descending numbers being unintuitive.

Why? Because "higher number is better" is NOT, I repeat, NOT some inherent, biologically or mentally determined principle, and therefore it's not something you can properly call "intuitive".
I mean no disrespect to anyone in specific, but over time I've become convinced that whenever someone complains of THAC0 being unintuitive, they in fact mean one of two things. The first is "I find subtracting a small number from another small number, let alone a single-digit negative number, to be too hard, or at least significantly harder than an addition of numbers, because my primary school math education sucked. However, I'm too narcisstic to admit to sucking at math, and too lazy to fix it with practice; so I'll just criticize the game instead."
And the other is "I want to belong to the cool kids, and the cool kids are all hissing and spitting and booing at descending AC, so I'll just mimic them without thinking about whether they're actually right or not."
The main "unintuitive" reason is what's better Plate Mail +1 or -1? Which lowers your AC and which increases it? Plate Mail +1 is what's better and lowers your AC. Would you guess that if you didn't know the rules? Maybe, but it's less likely that you guessing correctly 3.x's way.

Also your examples aren't good. Those are all rankings (which this isn't) or a countdown. You don't add or subtract rankings, "1st class - 3rd class = 2nd class" for example. I'll grant the countdowns, but you don't add to the countdown if the event countdown to is happening earlier (nor do you often move the event's time). You don't see "bonuses are minuses and penalties are pluses" in a system very often (The game show Debt was one such case). It's not some profound psychological truth that subtraction is harder than addition though.

3.X's system works better for a larger range of attacks and armor classes. A great wyrm red dragon has an AC of 41 and a BAB of 40. In THACO terms, this would be AC: -21 and THAC0: -20. So a dragon attacking another dragon with just BAB (mods cancel each other out or something) would use the following formula (Hit if Roll+AC>=THAC0) would be Roll+-21>=-20. It's the same as 3.X's (Hit if Roll+BAB >= AC) Roll+40>=41. The math works out the same, but you don't encounter negative numbers as often elsewhere.

THAC0 isn't a fundamentally bad system. It's just inelegant and doesn't add anything.