This entry is part 5 in the series Rules Mastery

In the course of part 2 of this series, which was all about overcoming a resistance to studying rules for their own sake, I suggested that the GM learning a new set of rules should watch for patterns, and use them to make understanding the rules a little easier.

Starting in this part of the series, I’m going to start explaining some of those patterns. and how rules systems inherantly contain two elements that form a foundation from which an understanding of all the other game mechanics and internal systems can be founded. These are the Rules Touchstones, your guides through the maze of the rules. The first of these is the combat system, and the second – which will occupy our attention in Part 6 – is Character Generation.

Styles of Combat system

The Combat System is the more important of the two. There are two basic styles of combat system, and they are distinguished by the damage-handling subsystem. Specifically, does damage penetrate defences or does it alter the probability of the inflicting of damage?

This distinction has ramifications throughout the rest of the combat system; identifying what type of system is in place provides a key indicator of what to look for in other subsystems relating to combat, and – by inferance and extension – how non-combat systems function.

Damage Penetration Systems

This is probably the less-familiar of the two. It is the system used by Rolemaster, and by classic Traveller, amongst others.

  • This type of system frequently has relatively consistent hit points from one individual to another, regardless of the level of experience/expertise of the individual;
  • Attacks generally hit the target;
  • Armour and other such defences subtract from the amount of damage inflicted;
  • Combat resolution may take the form of opposed rolls, or both attack and defence may be fixed numeric values determined from the individual’s stats;
  • If both attack and defence are fixed, damage will be more variable, and may include some ‘exploding’ componant;
  • If attack resolution is by opposed rolls, the damage may be fixed by weapon type;
  • Damage is often broken into different types with different effects.

Damage Penetration-style systems are better suited to highly-specific detail-oriented approaches, as that last point implies. It is often a question not of how much damage a particular weapon or attack inflicts, but how much damage it inflicts when opposed by this type of armour as compared to that. This means that each type of pole arm has a completely different set of combat characteristics, for example, which is a far more accurate reflection of the historical origins of such weapons.

This can make these systems slower but more realistic. In such systems, everything has to be placed in its proper context before it can be meaningfully interpreted, and many of the values that d&d players expect to be fixed aren’t, and vice versa.

Probability Alteration Systems

The alternative is to define the target value of an attack roll not as the number needed to hit, but as the number needed to both hit and inflict damage. In this context, armour no longer absorbs damage directed at the wearer, it alters the likelyhood of damage being experienced at all.

This is the basic approach employed by D&D since the game first came out. It has quite different characteristics to the first system considered:

  • This type of system frequently varies the number of hit points to reflect increased skill in battle;
  • Attacks often do not hit the target, but when they do, they usually automatically inflict damage;
  • That’s because armour and other defences don’t alter the damage done, they reduce the likelyhood of damage being experienced by the target;
  • Combat resolution rests on a single die roll with circumstancial modifiers which must achieve a target value, based on the defender’s ability and protection, or better;
  • Damage per blow is relatively fixed within a narrow range;
  • Damage is usually treated in a collective manner, without distinguishing between different types such as crushing, slashing, stabbing, electrical, fire, etc.

Probability Alteration systems are more abstract, and better suited to less realistic combat modes, with far greater capacity for the fantastic. A given weapon design will usually inflict the same amount of damage with the same level of variability regardless of what sort of armour or protection the target has.


Some game systems are a complex hybrid of both types. The example with which I am most familiar is the Hero System, in which each of the key factors is inherantly variable. While this has benefits in terms of flexibility, it can also increase the risk of strange synergies and loopholes within the rules that produce unexpectedly severe or mild results.

Where there is one complexity, there is usually another, and then another. Not only does the hero system distinguish between two types of attack modes (killing vs standard attacks), it distinguishes between three attack types (physical, energy, and mental), and it distinguishes between two types of damage (stun and body), and on top of all that, it is replete with exceptions to all of these, where different attack types are given unique combat resolution systems – flash attacks, transforms, presence attacks, and so on. And, over the top of that layer of complexity are all the modifiers that can be applied to distinguish one attack from another – Armour Piercing, Penetrating, No Normal Defence, and the like – and multiple kinds of defence, such as force fields, armour, ablative armour, etc.

Combat As A Systems Touchstone

Entirely aside from the fact that combat is a major element in any RPG campaign, and hence any increase in understanding the combat subsystem is a valuable achievement in and of itself, the combat system is a key to a number of other elements in most game systems.

Perhaps the most obvious point of connection between the combat system and the rest of the game is the approach that the rules system takes to skill resolution. The truth of this statement is easy to prove: pick any game system that you already know and consider the similarity between the way attack rolls are resolved and the way skill tests are resolved. Are modifiers applied to the roll, to the basis of the roll, to the size or number of dice rolled, or to the target to be achieved? How large are the modifiers? How are they determined?

How is success or failure determined? How are fair fights scaled? Is the system more detail-oriented, or more abstract? How does magic or technology (as appropriate) interact with the system? How is perception figured? How are ranges handled (more on that in part 7 of this series). How are tactics and circumstances translated into game mechanics? How do characters improve their abilities? How about movement?

There are few subsystems within the mechanics of any game that intersect with so many other parts of the overall game system. That’s why the combat system is one of the best possible places to start when learning a new system, as recommended in the third part of this series, and why it is one of the two rules touchstones.

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