Creating house rules, custom rules specific to a local group or campaign, has been common throughout the history of D&D. What makes an effective house rule or game hack and what, if anything, makes early D&D (say, pre-WotC D&D) hackable?

Some properties of early D&D that might contribute to this tendency include mechanical simplicity, reliance on subsystems, intuitive abstractions such as spells, classes, and monsters, avoidance of deep interrelationships between rule areas, and clear and powerful core game loops. Perversely (from the perspective of a designer, at least), some degree of roughness, inefficiency, or lack of rules clarity might also motivate house ruling. Some of the properties that contributed to hackability probably arose historically due to the gradual evolutionary nature of D&D development, but whether the properties are emergent or designed top down is irrelevant to the functional behavior.

Collectively, this set of properties provides what I will call articulation points, which support both deep (structural) substitution of rules subsystems and shallow (content) addition of mechanical elements. For an example of a deep articulation point, consider the XP/advancement  rules. One could swap out the treasure XP rule for something like a quest fulfillment rule. This would change the dynamics of gameplay in some ways, but would not seriously interrupt the moment to moment experience of play or the core game loop. For an example of a shallow articulation point, consider the “spell” game abstraction. One can write custom spells to replace or supplement the official spells. (Character classes are another similar shallow articulation point.)

A game is articulable to the degree that it is robust to modification in this way, providing a strong but flexible internal structure that continues to function in an understandable manner (even if the dynamics shift) when articulated both deeply and shallowly. Early D&D, especially of the “basic” variety, is particularly articulable.

Practically speaking, one could diagram out the various deep and shallow articulation points provided by a game to guide effective house ruling. Thus, the game provides a structural chassis, much like an automobile prior to factory finishing (or modding). Additionally, and perhaps of more collective utility, mapping out a shared understanding of an underlying chassis would provide an easy way for game designers to offer custom or campaign-based “modding kits” for games while reusing existing design and minimizing wheel reinvention.

Upon consideration, such a chassis ends up being a collection of purposes that fully instantiated rules must fulfill, rather than methods or procedures for fulfilling such purposes. As such, one can think of the chassis as factoring out the teleological structure of a game. A connected mesh of whats and whys isolated or distilled from the hows.

This conceptual approach seems subtly different to me than some common previous ways of thinking about and sharing house rules. One previous approach is standardization, similar to a brand marketing or software compatibility model. One can share a new class “for” (compatible with), say, Sword & Wizardry. Or use the stat line expected for an Old School Essentials monster. Another approach is presenting the (misleading) facade of an entirely new game that has the benefit of (maybe) standing alone more effectively (that is, requiring less tacit subcultural knowledge) but has the downside of being less obviously useful as a source of articulations to other games and creating an unwarranted veneer of incompatibility for players less familiar with the subcultural history or context.

So much for the articulability of early D&D (the chassis side of the equation). What about the house rule (mod, articulation) side of the equation? A good house rule should fit into a clear articulation point, avoid spanning too many elements within the overall chassis (as this increases overall brittleness), and should be clear about whether the modification is deep (such as replacing the XP advancement subsystem or combat initiative subsystem) or shallow (adding/replacing new classes, spells, monsters, and so forth), as mixing deep and shallow creates a player interface with many special cases that need to be remembered. Probably some other things as well that I have yet to consider.

There are many broad functions that rules can have. Here is one: representing the details of a broader fictional world. The fictional world might not work exactly like the world of day to day phenomenological experience that we inhabit and experience as the real world, but it nonetheless makes sense, loosely speaking. Sure, monsters might exist that we have never encountered and sorcerers might be able to, with long study, cast spells to open portals. But there remains the basic assumption that behind the scenes there is a living, breathing world that both shapes and constrains the shared imagination of play.

Call these reflective rules. Rules as the physics of the imagined world. That is, the rules reflect the imagined campaign. In reflective rules, the cause is (conceptually) outside the formal game elements. A rule is a good rule if it produces logical and realistic outcomes, relative to the shared understanding of the campaign setting. This is a common-sense vernacular approach, and it has had a wide currency, arguably undergirding most mainstream tabletop roleplaying games from varieties of TSR D&D to Rolemaster to D&D 5E. The assumption that rules should reflect the campaign world is something like the equivalent of Literary Realism for tabletop roleplaying games. It is the equivalent of what you get most of the time if you watch a serial drama on Neflix or pick up an airport novel.

Here is another function rules can have: determining the situations and details of play. Call these formative rules. The results may or may not make sense fictionally, but they are the rules, so you execute them and then interpret the outcomes as best you can. The fireball might detonate in a square. The random encounter generates a dragon one hex outside of town, three times in a row. The rules form the situation of play. In formative rules, the cause is (conceptually) the rules themselves and interpretation happens (if at all) subsequently. When one stocks a dungeon using the B/X procedures presented on page B52, the outcome is not really intended to model any kind of naturalistic situation. It might, but the goal is not logic or naturalism. You need monsters and treasures and traps in some rough distribution for the game to work, so the rule does that. Consider traditional spell slots. Sure, there is some very loose Vancian inspiration, but really original style D&D spells need limits of some sort to support challenges. Fire and forget is a way to do that. If one adopts the approach of assuming D&D is always right, that is in the mode of formative rules.

The most effective formative rules are designed to generate the dynamics and situations necessary to a particular game. They create satisfying tension and result in outcomes where player decisions matter. They can provide oracles into the imagined world. They might facilitate complex tactical contests or generate genre-appropriate thematic outcomes. Formative rules can also provide practical support for simplifying or abstracting elements of an imagined world which might be impractical to model explicitly. Additionally, the interpretation and reconciliation required by occasionally illogical results can serve as an engine of creativity. What might explain three dragon encounters in a row, so near to civilization? However, thoughtlessly designed or applied formative rules can be a straitjacket or procrustean bed, trapping players in abstract or solipsistic formalism, rewarding optimization and homework.

Does this matter, or is it just semantics, another arbitrary taxonomy to create more specialist language? It seems to me that the potential of the form, what tabletop roleplaying can uniquely provide compared to other forms of entertainment, media, and art, involves a fusion of these two modes.

If one leans too heavily on formative rules, where players weave results into some shared narrative fabric unrelated to any ideal of living breathing world, one risks losing the richness of possibility inherent in the idea of a campaign with integrity. Pathologies of formative rules include repetitive outcomes and the peasant railgun. That idea of the campaign world as external, causal source, along with some degree of shared commonsense understanding of how things work, is what enables principled and flexible rulings at the table.

If one leans too heavily on reflective rules, where logic and verisimilitude dominate, one gets lost in minutiae unconnected to the experience of play. Pathologies of reflective rules include, in the D&D context, Shopkeepers & Spreadsheets and fixation on realistic fictional economies at a level of detail far exceeding relevance to play. The OSR etc aversion to extensive fictional histories and backstories is not just a practical norm, nor is it just a rejection of tabletop roleplaying as a thespian concern; this aversion is also a recognition that the most useful elements of setting are those that provide contact surfaces for play at the table.

Ideally, a campaign is both internally consistent and makes sense on its own terms, broadly speaking, but simultaneously provides a stage for play with all of the concerns that entails. The reflective and formative components can feed back into each other, providing mutual enrichment. Some idiosyncratic element of a campaign setting might emerge from a seemingly illogical random stocking result (formative) later interpreted and explained in the logic of the setting, informing later concrete details and rulings experienced by players in play (reflective).

I tried real hard to avoid bogging this post down with technical jargon. However, to give credit where credit is due I will note that these ideas are related to formative and reflective constructs in the philosophy of science. This article is a good on ramp:

Edwards, J. R., & Bagozzi, R. P. (2000). On the nature and direction of relationships between constructs and measures. Psychological Methods, 5(2), 155–174.

Is there a “founding myth” of OSR? Here is one proposal:

The founding myth of the OSR, that it is based either in an original play style or in the Gygaxian style, … My view is that many of the communities, past or present, which identify with the “OSR” are based on that myth despite it being inconsistent with the multi-various ways in which hobbyists played in the 70s and 80s, as well as with the specific vision of D&D which Gygax propagated.

— Marcia B., Addendum

At first glance, it does seem like discovering an original play style, or original authorial intent (and perhaps design principles) is an attractive project. For example, here is James of Grognardia writing in 2008:

… “D&D is always right,” by which I mean that the ideas and concepts we got in OD&D, whatever their origins, must be the standard by which we judge everything else. Enough things weren’t added to OD&D that I can only conclude that, if they were there, they were there because Gygax and Arneson both signed off on them and deemed them a good fit for the game they’d created. … In the end, though, OD&D was written according to a certain vision and I think that vision is both recoverable and worth investigating.

— James M., June 2, 2008 comment

However, in the context of other discussion around that time, and in further recent conversations, I think it is clear that the goal (here at least) is not to recover some pure Gygaxian canon, brilliant and untarnished, but rather to assume that there may be some value in a rule or game element, whether or not it was an intentional creation, and see where that assumption leads. This was certainly the approach I took when, inspired by Dwimmermount session reports, I started my Vaults of Pahvelorn campaign taking only the 3 LBBs (core OD&D) as base rules chassis. This necessitated substantial interpretation and invention given the patchy disorganized nature of the game and text, but for me was more about personal creative constraint than about traditionalism for the sake of tradition or about nostalgia (I didn’t even know OD&D existed until around the time I discovered Grognardia).

Many strands make up artistic or hobby movements and scenes, arising from the various and idiosyncratic priorities of participants, so it would be surprising if one could come up with a simple explanation or single goal that unifies a scene. While some of the impetus might have been exegesis, other motivations might have involved connecting with old friends or (as Richard writes) resisting the then-current dominant practice that was being marketed by Wizards of the Coast. That is by no means an exhaustive catalog.

Trying to distinguish between genuine cultural genealogy and founding myths has led to claims about the invention of tradition, where someone (or a group) takes a novel idea but frames it as traditional in order to increase legitimacy. One can find many examples of this in the history of ideas. Here is one that approaches prototypicality. In ancient China, explicit innovation was not a winning rhetorical strategy. Instead:

Authorship as an act of creation was a fraught notion in traditional China, since true “creation” (zuo 作) was reserved for sages. Already Confucius embraced instead “transmission” (shu 述) as a weaker form of agency indebted to an imagined higher authority.

— The Oxford Handbook of Classical Chinese Literature, p. 344

That is, Confucius (and the others associated with his school of thought) presented his ideas not as invention or even synthesis, but rather as transmitting the already revered wisdom of sage kings, the original culture heroes of China. Though I am curious about the historical development of play styles, I am not sure Sage Gygax has much cultural currency in this manner. Maybe someone could find some forum scenes that lean in this direction if one looked hard. And many OSR norms and assumptions do not seem to reflect past practice or texts. For myself, as grab bag of inspiration and techniques, how people actually played (or what is written in old texts) seems potentially useful, but not as prescription with sacred imprimatur.

Sometimes I think about all game rules and supplements in terms of prosthetics. Broadly speaking, a prosthetic is an artifact to replace a missing body part or remediate some deficiency. Some prosthetics are useful to almost everybody sometimes (stepladder) while some remediate a common deficit (glasses) and others are highly idiosyncratic. Similarly, the tasks referees and players need help with when playing a roleplaying game are various. Some seemingly common prosthetics include procedural systems to resolve fictional violence and guidelines to come up with fictional people having inner lives with some degree of complexity (such as non-player characters). Or how to decide how much fire a wizard can conjure.

So how does one decide what aspects of a game deserve elaboration and which can be left for the imagination of the players? What counts as design that punts where it should run? There is an essentially relativist objection to general standards for what deserves elaboration. It is hard to get beyond this subjective hurdle to make truly general recommendations without doing extensive observational research that people have not so far seemed interested in or resourced to do, especially for tabletop roleplaying games specifically.

For example, I have a low tolerance for certain kinds of hassle in rules, so I designed a lot of my mechanics as a prosthetic for that. Who knows what proportion of players are happy to track coin weight encumbrance exactly with spreadsheets or whatever? And might even enjoy it? I suspect that proportion is lower than players for whom slot based encumbrance would be more functional, but I lack the data, and I doubt anyone has much evidence relevant to this question beyond common sense platitudes and personal anecdotes.