The Perception Check of OD&D

Author: DHBoggs / Labels: , ,

Over the past year or two, I've watched a lot of D&D online, including 5e games, and perhaps what jumps out at me most is all the "checking" going on, often with an ensuing discussion over what stats apply.  Typically, the check called for will be a "Perception" roll.

In many situations, these checks will occur when, were it my game, no roll would be needed.  I would pass along the information as something the players could and would reasonably discover without any need to breaking the immersive narrative by a pointless dice roll.  

I'll give a real example, pulled entirely at random from a series of random clicks on Youtube videos that I hadn't watched previously.  I took me all of about 5 minutes to find one:

Player: "Do we see any remains of the ship or anything like that?"

GM: "Give me a perception check for anyone looking around for stuff like that,"

(source was D&D Live Play The Dungeoncast Presents: The Vault Raiders and The Isle of Dread - Part 1 )


I'm not criticizing the GM here or in any of thousands of other similar game play examples.   I'm merely pointing out that these checks are a constant part of play in today's gaming.

Here's where you might expect me to say that old school players don't do this sort of thing.  But I won't, because we do and we always have.

It's the frequency of rolls, and the expectation of easy answers, that are the main differences.  Meaning, typically the GM will ask for, and the players will make, a "Perception check" in lieu of having the character actually go and examine something through role-play.  

However, there will always be times when it's not straightforward what the characters might notice, whether they are actively looking or not.  For example, what are the odds they notice that is a real set of eyes staring at them from behind that painting?  So the question isn't should or shouldn't we ever have checks, but how and how often.

There's no set way these "old school" perception checks are made. Perhaps the most common method is to roll against the Wisdom score and that often suffices.  After all you can't be wise without first being perceptive.

I can't speak for what Gygax may have thought of the "perception problem" but it did occur to Arneson in at least one instance when preparing supplement II.

Take note, if you will, of this passage from Supplement II page 3:

"There is only a 5% chance that an assassin will be recognized when in disguise, 10% if the assassin is posing as a member of the opposite sex. Disguise checks should be made daily. Modify the chance downward by 1% for each 1 point in combined intelligence and wisdom below 20 which the intended victim has, i.e. a victim with a combined intelligence/wisdom score of 18 has only a 3% chance of detecting the assassin. For every combined intelligence/wisdom point above 24 the intended victim has a ½% better chance of detecting the disguise, dropping all fractions, so an intended victim with an intelligence/wisdom score of 31 has an 8% chance of spotting the assassin (31 — 24 = 7 × ½% = 3½% = 3% with dropped fraction of ½%)."

Arneson here is providing us with a method for a character to perceive something hidden - in other words a perception check.

The check involves combining two statistics - a technique we see Arneson use a lot in various ways in the '70's, from the ego battles of magic swords to multiple examples in AiF, and frankly it makes sense.  There's no need for new stats when a combination of the old already covers it and further, makes those stats even more central to the game.

So let's break down how this works:

First, the GM assigns a base chance something might be discovered in a set time period.  For the assassin, it was 5% a day, but it could be some chance per turn or hour or whatever is appropriate.  Note that unlike a straight Wisdom check, it isn't a flat number, but takes into account the difficulty of the situation.   In other words, the GM sets a kind of "DC" value with a frequency component.

Second the chance is modified by the combined Wisdom and Intelligence score total.  A bonus is granted if the score is more than 24 and a penalty is applied for totals below 20.

These numbers don't change, and can be written down on a character sheet as a +/- number - call it the Perception Modifier.

So for example, a character with a Wis of 14 and Int of 9 (14 + 11 = 25) has a +1 bonus.  The highest bonus possible per the Assassin rule is +6 but surely only a god has those kind of scores!

Now the question arises of how to apply the bonus or penalty to a die roll.  The example of the Assassin uses a percentile check, which may make sense for that case but is hardly applicable to something like noticing a strange stain on a tapestry or the special pendant worn by an orc.   For these kinds of cases the GM must make a judgement call.

Fortunately, we can turn to Dragon Magazine (#133) for a bit of advice from one Thomas Ruddick in an article he wrote on Perception.  Mr. Ruddick reminds us that: 

"Perception is important to all character classes, as it affects the character's chances to notice things that might be important in the course of the game." (p12)

Ruddick advocates for a separate Perception stat - but we definitely don't want to go down that road.  More useful for us, however, is that when it comes to checks, he advises rolling different dice: 

"....arguments about whether or not a character is or isn't a light sleeper are avoided with a simple 1d20 roll against perception.
Characters who want to search for hidden items, clues, or persons in a crowd may also use this 1d20 perception roll. Characters should likewise be given some odds for success if searching for secret doors, traps, and other things even if they have no previous skill at finding such items; a 1d100 roll vs. perception would probably be appropriate in most situations." (p14)

Choosing between 1d20 or 1d100 is practical, and in line with the Assassin rule.  It allows us to apply the "Perception Modifier" to greater or lesser effect depending on the situation.  For characters who have neither a positive nor negative modifier - as will often be the case - it won't matter what dice are used.

So here is what I'm proposing, step by step:

1) First, the GM must assign a % chance something will be noticed and decide how often the characters will have an opportunity to roll.  To quote Ruddick again. "To find the appropriate check in these situations, the DM must consider the relative difficulty of the act of perception in the game" (p14)

2) Once a chance is decided, the GM must decide whether a d100 or 1d20 roll is appropriate for the particular character in question, when a Perception Modifier might apply.  For the majority of cases, ranging from easy to moderately difficult, use 1d20, for extremely difficult situations use d100.  If 1d20 is being used, the chance to succeed must be converted to 1- 20.

3) Apply any Perception Modifier to the target number.

4 Roll under to succeed.

6 comments:

Melan said...

I believe there are two other, perhaps more analogous OD&D mechanics which resemble perception rolls:
1) Finding secret doors and traps, rolled on 1d6. Elves and dwarves benefit from a higher rating, and "passive perception", which is rolled by the GM without a player call.
2) Surprise in combat. This is a flat, GM-facing 1d6 roll in the LBBs, but special cases are introduced later for various character types and situations.

If I were to introduce a perception mechanic in OD&D, this is the route I would take. I would use a GM-facing 1d6 roll with odds based on character type and situation. Keeping with OD&D's emphasis on player skill,
1) I would let players automatically detect anything notable on an active declaration of checking their environment.
2) I would roll for "passive perception", and would perhaps restrict it to characters in the first rank, and only if equipped with adequate light sources.
3) I would only apply this mechanic in special situations. Trivial things would always be noticable.

DHBoggs said...

Thanks Melan - great comment. I agree with your points and that a d6 based method is perfectly in sync with the rules. The one benefit of applying the "Assassin method" if you will is that it takes into account high and low ability scores and can provide some characters a bit of a bonus.

Charles Saeger said...

There’s one other instance that springs to mind, and this time it is Gygax: Pick Pockets. From Greyhawk, pp. 11-12:

“ A score above the indicated percentage means failure, and no further attempts may be made. Also, there is a chance that the one who is being pickpocketed may detect the thief. To determine this, for each level above 5th, the victim has a + 5% chance of detecting the “lift,” so a 10th level, for example, would reduce the pos- sibility of a successful attempt by 25%, i.e. if a base 100% it reduces to 75%.”

AD&D goes a little farther. PHB, p. 28:

“ Picking Pockets fails if a score above the percentage shown for the level of thief attempting the function is generated. If the score is 21% or more above the number shown, the victim notices the thief's attempt. The potential victim reduces the thief's chances for success by 5% for every level of experience he or she is above the 3rd, i.e. -5% at 4th level, etc. For example, a high level thief (Master Thief, 12th level) is planning to pick the pockets of a magic-user he has noticed nearby. The base chance for success is 100%, the thief is a half-elf and adds 10% for racial ability; the thief also has 18 dexterity ability score, so another 10% is added. This totals a nice, safe 120% — can't fail! However, the victim happens to be 12th level also, so the subtraction is 9 × -5% = -45%. This brings the chance for success down to 75%. A good chance, but if 96% or higher is rolled, the thief will be noticed, and …”

Robert said...

Melan - that's exactly how I judge on the matter! Spot secret doors = passive perception, roll for each PC, maybe a character sees something (let's say, outline in the wall). Active searching for 1 turn (...roll for monsters) locates secret doors/passages automatically.

Unknown said...

Shaking my head.

Dan, You've said it for me.

All tha rolling is ridiculous.

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