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Thread: [AD&D] Why THAC0?
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2009-06-06, 01:18 PM (ISO 8601)
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[AD&D] Why THAC0?
This thread has been started to prevent further derailment of this thread: [4.0] Insults intelligence.. Yeah, a bit edition war like, but THAC0 is actually a really interesting subject so I want to continue the discussion here. Much of the debate seems to hinge on two different definitions of Armour Class:
Originally Posted by D20Originally Posted by AD&D 2e
Nah, you apply all modifiers separately to avoid confusion. There is no speed difference in rolling a die and adding a modifier, but it depends how you do the actual in play event. I have heard of people saying stuff like "I hit AC 3", or something along those lines, instead of calling out their roll, in which case the calculation would need to be done before hand.
However, it can also work like this
Target Number = 21 (always)
Player: Rolls Dice, adds fighting ability and any other modifiers
Game Master: Adds armour class of target to the total, if it equals or exceeds 21 it is a hit.
Alternatively, THAC0 eliminates fighting ability and becomes the target number, but all the player needs to do then is:
Target Number = THAC0
Player: Rolls dice and adds modifiers
Game master: Adds armour class of target and checks target number.
The second edition one? Yeah, I think that optional rule is about the only instance. The more I think about it, the more convinced I am that the diversity of methods of calculation are in fact what leads people to believe it is "counter intuitive". Indeed, THAC0 could stand for the entire second edition game in that respect.
Do not not modify THAC0. That is why virtually everything is expressed as a modifier to the attack roll and not THAC0. The modifier is always the same [e.g. positive or negative], and that is why THAC0 works the way it does. Trying to modify THAC0 in AD&D is like trying to modify your opponent's armour class by your attack bonus in D20/3e.
Let's take an example:
A 5th level fighter with 17 strength has +1 to hit. He is also wielding a cursed sword, which is imposing a −1 to hit. In addition, his target is enjoying the effects of a prayer spell, imposing a further −1 to hit.
The player attacks his opponent and rolls a 13, which he modifies by −1 to get 12. The game master checks the armour class of his opponent, which is 5 and adds it to the result to get 17, which is better than his THAC0 of 16. A hit has been scored.
In this instance, the player was told there was a prayer effect in play and asked to modify his attack roll accordingly. If the game master had wanted to keep that secret, then he could have applied the same modifier to the armour class of the target.
It's the same process:
Roll die, player modifiers added, game master modifiers added = THAC0?
Roll die, player modifiers added, game master modifiers added = Armour Class?
The only difference are that the game master almost always adds a modifier by way of armour class in AD&D, and that in D20 the modifiers are typically much larger. The trade off is that in AD&D negative modifiers are always good for the defender, and positive modifiers always good for the attacker.
If the game master needs to look at the player sheet it means he does not have their THAC0 already available, but he should have their THAC0s and that of all the combatants in play available, just like he should have their armour classes available in D20. That is not extra math, it is just like having BAB noted separately from AB.
Again you misunderstand. You are assuming these terms:
My plusses are good for me
My minuses are bad for me
His pluses are bad for me
His minuses are good for me
In AD&D it is:
Plusses against him are good for me
Minuses against him are good for me
Plusses against me are bad for me
Minuses against me are bad for me
Neither is more intuitive than the other.
Not always, of course, not on AC 0. However, I do not really think that you can make the case that there are typically less modifiers in D20 than AD&D.
Pluses to the roll in AD&D are good for the person rolling the die, minuses to the roll are bad for the person rolling the die. Same in D20.
This initial idea that Armour Class is a number to be overcome, rather than a modifier to a roll. That is completely non intuitive, since "armour class" does not denote that at all except by learned exposure. If it were called "defence rating" you might have a point.
On what basis do you conclude that armour class is a number to be overcome when in fact it only is in D20? That is purely subjective on your part. In Chainmail, for instance, Armour Class is a number cross referenced against Weapon Class to find the probability of a kill on the man to man melee table.
Armour classification is just that, the class of armour. You add it to the attack roll (or deduct it from THAC0 if you prefer). This is the sort of statement that leads me to infer that you are are unfamiliar with the design approach of AD&D, in that you are imposing the conceits of D20 onto the game system and coming to an erroneous conclusion.
The above list of bonuses makes no case at all. These are all modifiers to the attack roll and not bonuses to a number to be overcome.
That is actually wrong. Magic and dexterity do not give a bonus to armour class, they impose negative penalties on the attack roll. You can roll them into armour class (which is commonly done), but that is not the actual armour class (which is a number in AD&D used to find bonuses to hit versus weapon type).
Yeah, it is just that. The "modified" armour class is a short handed rolling up of bonuses and penalties to make the game go more quickly, but armour class is literally class of armour.
Wrong, I am afraid. Armour Class is right there in Chainmail, but reversed so that higher is better. Arneson is reported to have taken inspiration from the Naval game, but armour class was already part of the Chainmail Combat system. There is a reason that hit charts in OD&D only go down to AC 2 despite the presence of magic items.
Nope, the charts were extended in AD&D (and in Greyhawk) for ease of play, but the actual "rolling up" process is not armour class in its primary sense, though "armour class" is used to denote the secondary meaning in almost all short handed instances. The difference is important when you are dealing with the repeating "20" rule or when using weapon type versus armour class.
Here is the original wording:
Monsters & Treasure, p. 31:
ARMOR: Armor proper subtracts its bonus [Note: here we are talking magical bonus] from the hit dice of the opponents of its wearer. If the shield's bonus is greater than that of the armor there is a one third chance that the blow will be caught by the shield, thus giving the additional subtraction.
a) The Armour Type's Armour Class.
Armour protection is measured by Armour Class (AC), a number rating; the lower the Armour Class number, the better the protection.
Armor Class (abbr. AC)--a rating for the protective value of a type of armor, figured from 10 (no armor at all) to 0 or even -10 (the best magical armor). The higher the AC, the more vulnerable the character is to attack.
Defensive Adjustment applies to a character's saving throws (see Glossary) against attacks that can be dodged--lightning bolts, boulders, etc. It also modifies the character's Armor Class (see Glossary), representing his ability to dodge normal missiles and parry weapon thrusts. For example, Rath is wearing chain mail, giving him an Armor Class of 5. If his Dexterity score is 16, his Armor Class is modified by -2 to 3, making him harder to hit. If his Dexterity score is 5, his Armor Class is modified by +2 to 7, making him
easier to hit. (In some situations, beneficial Dexterity modifiers to Armor Class do not apply. Usually this occurs when a character is attacked from behind or when his movement is restricted--attacked while prone, tied up, on a ledge, climbing a rope, etc.)
Now here is the exchange in question:
I can see that this has caused some confusion. My intention was to distinguish here between two forms of armour class. The base armour class is determined by armour type (used for weapon type versus armour class adjustments, if used) and the short hand that rolls all modifiers into a defensive value also termed "armour class". Armour Type is not a bonus to "armour class", it is the "base armour class" ranging from 10 to 0. Take your example for instance:
Plate Mail +1 (say) = AC 3(2)
Dexterity 18 = −4
Modified Armour Class = −2
A first level fighter needs "20" to hit that Armour Class in second edition, but if he has a +1 sword he doesn't suddenly need "19". He still needs "20" because the modified armour class deducts from his "to hit" roll. That's why armour itself only has a base classification system between 0 and 10.Last edited by Matthew; 2009-06-06 at 01:24 PM.
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Re: [AD&D] Why THAC0?
I always thought the reason THAC0 existed was to keep information away from the players. The players weren't suppose to know the AC of the monsters they're facing. If I recall correctly (and I probably aren't), the original intention was that players aren't even suppose to know their own THAC0. There was a reason why the THAC0 chart was on the DM screen. The DM was suppose to be the only one to figure out the target "to hit" number based on the PC's THAC0 and the monster's AC because he was the only one with both pieces of information. THAC0 was there to maintain the illusion so the PCs can't "peek under the hood" so to speak. The only thing the PCs were suppose to know after rolling their dice was "hit or miss".
This is the only reason I could think of to explain the roundabout nature of THAC0.Last edited by nightwyrm; 2009-06-06 at 01:34 PM.
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Re: [AD&D] Why THAC0?
If I'm not mistaken, in original 1e D&D, there was no thaco or anything like it. Instead, you rolled a d20 and consulted a table which had every single monster on one axis and the player character levels on the other. I'm not 100% sure on the specifics.
What I do know is that when 2e came around, THAC0 was developed as an abstraction of this graph. Because they operated on the same function as the chart, THAC0 and AC end up decreasing as you become more formidable.Last edited by Human Paragon 3; 2009-06-06 at 02:00 PM.
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Re: [AD&D] Why THAC0?
Yeah, that's what I thought. When the math behind THAC0 and AC was created, it was information that should only have been available to the DM. The way THAC0 and AC works makes perfect sense if the DM was the only one with the information.
The player was suppose to roll the dice, add/substract any modifiers and give that number to the DM. The DM determines the target "to hit" from the PC's THAC0 and the monster's AC (or looks up the chart from 1e) and tells the player whether he hit or missed. The player was never suppose to do anything with his own THAC0. He was suppose to be able to play perfectly fine without even know what his own THAC0 was.Last edited by nightwyrm; 2009-06-06 at 02:02 PM.
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Re: [AD&D] Why THAC0?
I always thought the reason THAC0 existed was to keep information away from the players. The players weren't suppose to know the AC of the monsters they're facing.
Ultimately, using THAC0 gives exactly the same effect as the system in 3.x, but the 3.x system is simpler and easier to use. OK, maybe it's only a little bit simpler, but it does have an advantage over THAC0, and I've never seen anyone argue that THAC0 has any advantage at all.Time travels in divers paces with divers persons.
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Re: [AD&D] Why THAC0?
But the 3.x player knows his own BAB. He can figure out that the monster's AC was 19. If the 2e/1e player weren't suppose to know his own THAC0, then even if the player hit on a 19, he can't figure out what the real AC of the monster was because he doesn't know his own THAC0.
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Re: [AD&D] Why THAC0?
THAC0 exists for the players so they can figure up their target hit without knowing the AC.
Roll, do math with modifiers, Players say I hit AC 3. DM looks at monster and sees AC 2, says sorry you didn't do good enough to to any damage.
THAC0 is really simple when you look at it.
THAC0=15
AC=0
You need to roll a 15 to hit.
Your sword is +3.
There is some race or buff in action that gives you a penalty of -2.
You roll a 14.
Dice roll + bonuses + penalties = modified roll
14 + (+3) + (-2) = X
14 + 3 - 2 = X
17 - 2 = X
15 = X
The modified roll is 15. You were targeting an AC 0 thing and your THAC0 was 15, so you hit.
THAC0 was all addition for the algebra.
All it was was THAC0 giving you the target numbers for anything you would ever come across. You just had to modify the dice roll to compare to that number along the number line. That number line represents all the AC range.
THAC0-AC=target number
15-0=15
If the AC was 2
15-2=13
If the AC was -2
15-(-2)=X
15+2=17
Thac0 15 needs 17 rolled to hit AC -2.
That is what THAC0 tells you, the target numbers for ACs. A player need only know his known modifiers to tell what the roll could have hit. Then any hidden modifiers the DM would add after the AC capable of being hit could be figured in.
Ages 12 and up usually means 6th grade, and by then isn't every taking basic algebra still? So where has the problem been with THAC0?
You are slightly mistaken.
II. ATTACK MATRIX FOR MONSTERS (Including Goblins, Hobgoblins, Kobolds, and Orcs)
Then each class had a table that was similar.
Class level at top, and ACs down the side.
It is exactly the same thing as THAC0 but takes up 3 pages rather than the little amount of space the THAC0 table takes up.
You want tables based around THAC0, it isn't that hard to do.Last edited by shadzar; 2009-06-06 at 02:28 PM.
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Re: [AD&D] Why THAC0?
At a certain point, it became assumed that players knew their own THAC0. THAC0 had the biggest box on many a TSR character sheet, IIRC. This was true even in AD&D.
There was nothing wrong with THAC0. D20 makes a minor improvement, making hitting stuff slightly more intuitive. It's not massively better, but it is a little bit better. Hm, I guess there is one substantive improvement. In AD&D/2e -10 was an arbitrary floor for AC, and that never made much sense to me. D20 did away with that (though many tables had already house ruled it away anyway).
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Re: [AD&D] Why THAC0?
I think Dave Arneson's "Tell me the number, I'll tell you if you hit" quote is applicable in this instance, mainly in support of the idea that - ideally - D&D should be as near as mechanically transparent to the player as possible.
More numbers means more abstraction, more meta-gaming (thinking about the rules, not the game), and more dissociation from the game world.
THAC0 should also be a cautionary tale of how legacy systems are sometimes more trouble than they're worth. AC as Armour Type made perfect sense if you had access to OD&D+Chainmail, but became gradually more opaque and esoteric as time (and editions) marched on and explanatory footnotes were excised or misinterpreted.Last edited by bosssmiley; 2009-06-06 at 02:32 PM.
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Re: [AD&D] Why THAC0?
I don't doubt that. But when the precursor to THAC0 (the "to hit" charts) was first created, it was intended to be DM-only information. They used the charts to created THAC0 and gave the information to the players but the math it was based on was suppose to facilitate DM usage only.
This is why it's awkward to try to figure out what monster ACs you hit from your rolls and your THAC0. It's suppose to be the other way around.Last edited by nightwyrm; 2009-06-06 at 02:35 PM.
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Re: [AD&D] Why THAC0?
That is kinda why they put it in the PHB afterall....
It is the way Dave made it up for armor based on ships and hull ratings.
Carry over from wargames that Gary kept using cause a simple number line with a limited range made perfect sense to the people that created the game.
What makes no sense to me is things today that still start at AC 10 still being weakest and going up to 50+ AC...why does AC need an unlimited range?
The floor wasn't arbitrary it was designed so allow for ease of functionality. You had a limit of materials you could use to make things from, and even magic had its limits on helping you. The mace may never have touched you from the magical protection, but that force of the blow still knocked you on your duff and caused damage!
What is arbitrary is 3+ editions having everything start at AC 10...what happened to 0-9?
But this is a thread about THAC0 so going any farther will derail outside of the AC system in conjuction with how it worked with THAC0.Last edited by shadzar; 2009-06-06 at 02:36 PM.
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Re: [AD&D] Why THAC0?
I just don't see how that's true. The PHB had THAC0 tables for each class, as well as to hit bonuses from strength. If you knew your weapon's plus or lack thereof, you knew your THAC0. The players were expected to calculate their own THAC0. Now, sure, the DM didn't tell you the AC of the enemy creature, but given a few near misses and near hits, any player could extrapolate the AC. E.g. my Thaco is 5. I miss on a 6 and hit on a 7. The monster has an AC of -2. It's just like D20, but with subtraction. No more or less was hidden from the player. You may be right that it wasn't the original intent to make the THAC0 known to the player, but by AD&D the player was expected to know it and the math behind it.
And yeah, -10 may have come from somewhere but that doesn't make it not arbitrary as used. Bahamut could dip himself in liquid adamantium and let it harden, then wield an enchanted WWII destroyer as a tower shield and he's still have an AC of -10, the same as a decked out high level fighter.Last edited by satorian; 2009-06-06 at 02:44 PM.
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Re: [AD&D] Why THAC0?
My intent was transparent like a car windscreen (invisible during use, but doing its job anyway). The players are left free to concentrate on play, rather than on juggling numbers.
Opaque? Yeah, that works too, in the rules are a black box to the players. As a player I have no problems with black box rulesets. "Input > witchcraft happens > output" is, IMO, good from the player's perspective.
Sorry. /derailmentLast edited by bosssmiley; 2009-06-06 at 02:50 PM.
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Re: [AD&D] Why THAC0?
Then completely arbitrary and without real reason, except they couldn't make the math work any other way with the d20 system.
At least with THAC0 you have a closed system that can be explained why THAC0 has the range it does.
Mathematically intuitive would mean d20 started with 0 for AC and got better, and they would make the dice roll comply with that.
Which is simple, d20-10 for the attack roll.
Also why no upper limit to armor? What can give better protection that magic or divine power? Some godslaying metal? Maybe armor made of Sapient Pearwood armor that moves the wearer to avoid an attack or something?
THAC0 can be adjusted to have AC start at 0 and end at 20 without saying roll a d20-10, can 3rd edition? (ignoring 3rd not having the limit of 20 AC for simplicity sake.)
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Re: [AD&D] Why THAC0?
Of course it's arbitrary. Lot's of things in games are completely arbitrary. Some in order to make the math work, some just coz the designer felt like it.
Why does the dagger do 1d4 damage, a short sword do 1d6 and a long sword do 1d8? Why are stats based on 3d6 instead of 3d8 or d100? There's no real reason for any of them. The original designers just decided to use what they did instead of something else.
I'm not quite sure what your complaint is...Last edited by nightwyrm; 2009-06-06 at 03:05 PM.
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Re: [AD&D] Why THAC0?
I can partially answer the weapon damage, but that is probably best for another thread...
The point is when looking at THAC0 you see a range including 0. BAB or whatever in 3+ has no 0.
Humans that understand counting know you start at zero and move out.
IE8 was once IE0 when it didn't exist, then IE1, etc.
How is it AC just starts at 10? There is nothing that can mathematically explain it because they could have made it start at 0.
They went to build the system around the dice rather than make a working system and make the dice work for it.
The priority, dice or system, I am calling into question. Making the system work and make sense would have the worst AC being 0, no AC at all. Weak frail humans wearing nothing but fleshy padding called skin.
The inability of the designers is transparent when you can see it was done just because they wanted to use a d20 for everything and couldn't figure a way to make AC fully intuitive.
THAC0 you can see it has a range AND includes that important number....0.
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Re: [AD&D] Why THAC0?
ummm....as a historical trivia, zero as a mathematical concept is not as intuitive as we may think: History of Zero
In any case, THAC0 has no 0 either, it goes from 20 to 1. AC goes from 10 to -10 so 0 is a part of the scale, but there's nothing special about AC 0 either, it's just one number in the scale.
The BAB system does have a 0, 0 BAB is what you start with. They can either have the attack bonus start at 0 or the base AC start at 0, not both if you still want something that works. Besides, neither the total attack bonus or AC have a upper or lower cap. You can have a AC lower than 10 if you don't wear armor and have a dex lower than 10.
Both the THAC0 and the BAB system have arbitrary parts to it to make the math work. And don't diss the math. Math working is what makes the whole system run properly.Last edited by nightwyrm; 2009-06-06 at 03:40 PM.
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Re: [AD&D] Why THAC0?
{Scrubbed}
EDIT: Before it's modded away, let me explain why. It's good design philosophy to make things simpler and easier! Just because you think it should all rely on Peano Arithmetic doesn't make it a sound decision to base everything in a game mechanic on number theory or whatever.Last edited by Roland St. Jude; 2009-06-06 at 05:25 PM.
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Re: [AD&D] Why THAC0?
abu, ty vole, what exactly are you getting at? I don't see how "simple is good" doesn't mesh with "math is necessary".
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Re: [AD&D] Why THAC0?
I gotta disagree here. AC10 is not the worst AC (it assumes someone with average Dexterity fighting with no drawbacks). Someone who was a blind (-2 AC), cowering (-2 AC) invalid (-5 Dex bonus) with the Vunerable flaw (-1 AC) would have AC 0, as in, anyone would be able to hit them. AC10 is the base AC because 50% of the time, someone unskilled but average will be able to hit someone equally unskilled but average on a d20.
As for THAC0, I really liked it, but then I like a lot of arbitrary mechanics and I've always had a soft spot for 2e.
Armor Class is a misonomer if you want to make the downward scale make sense. Maybe it should be Attack Chance, instead? Someone with AC10 would have a 50% chance of being hit by someone who is unskilled, but someone with a -1 AC would have no chance of being hit by someone unskilled.
if d20 + AC > Thac0 you hit. It's... pretty simple, really. Not the most intuitive, but hey. And then those plusses and minuses? You add bonuses to your roll. I don't get what all the problem is.
... though I still prefer 3e's method.
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Re: [AD&D] Why THAC0?
I actually think THAC0 is more intuitive than BAB/adjusted ability scores in some respects - it is a simple statement of what you need to roll to succeed in a particular situation (an average character wearing full plate armour and carrying a shield, IIRC).
AC is really an explicit version of the ad-hoc modifiers that a DM might want to apply to things like ability checks and thief abilities.
In reality, if the various mechanics for doing things had been made more consistent (leaving percentiles for situations where the only factor is chance), the end result would have been perfectly workable.
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Re: [AD&D] Why THAC0?
THAC0 itself is a shorthand for the attack tables, which were set up the way they were for two reasons: 1) For continuity between OD&D and AD&D (as Gygax mentions in the DMG), 2) On account of the "five repeating twenties" rule, which was the precursor to "20 is always a hit" (in 2e).
Actually, in this case you are all three mistaken. THAC0 does appear in the first edition DMG in the appendix. All Monsters are listed there with their THAC0 values for convenience. So, THAC0 was in the game from at least 1979.
All players should know their own THAC0 in second edition, though this may not be the case in first edition. The tongue in cheek introduction suggests that players peeking into the DMG should be severely chastised, but in actual fact anybody interested in the maths would have soon known about Fighting Ability/THAC0.
In Original Dungeons & Dragons the range was 9 to 2. The reason that −10 is the floor in AD&D is because Full Plate +5 and a Shield +5 = AC −10. It is literally the best AC you can achieve with armour (and shield was counted as armour), but it doesn't actually prohibit lower values, as can be seen in certain Dragons in 2e. Also, a range of 10 to −10 just seems good.
Indeed. The further you get from the initial idea the less it seems to "make sense."
You can certainly work out your modified THAC0 in 2e, though it is a bit of a pain to deal with inverted modifiers.
Yes, indeed. Both are entirely arbitrary scales on which to measure hit chances.
Until very recently I would have agreed with Chronos that there is just no advantage to the descending THAC0 system, and also that the AB system is a bit simpler and subjectively more intuitive (my girlfriend found AB bewildering compared to THAC0, and that is just the way her mind is set up, preferring small numbers I suppose or something). In recent months I have come to see why THAC0 and the descending Armour Class system might have a slight edge, and the reason is basically for totalling defence and attack modifiers. You never need to convert them when applying them to the dice roll, a −3 is always a −3 and a +4 is always a +4. The next step is eliminating THAC0 altogether in favour of Fighting Ability, which is essentially BAB or your fighter level. As a hybrid, I like that a lot.
Good discussion, I am enjoying it!Last edited by Matthew; 2009-06-06 at 08:35 PM.
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- Kanagawa, Japan
- Gender
It is a joyful thing indeed to hold intimate converse with a man after one’s own heart, chatting without reserve about things of interest or the fleeting topics of the world; but such, alas, are few and far between.
– Yoshida Kenko (1283-1350), Tsurezure-Gusa (1340)
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2009-06-06, 08:55 PM (ISO 8601)
- Join Date
- May 2009
- Location
- Mandelbrot set