Why GURPS defenses use half skill: A half-baked idea

Continuing the Games Diner’s fine tradition of bringing you the most inconsequential gaming gab out there…

Why does a Parry or Block in GURPS – figured as 3 + half your skill with your weapon or shield, respectively – use half skill, something seen pretty much nowhere else in the game? I asked that question in FEND, a bit of fun with rolling defenses like anything else, using full, normal skill. There, I opine that GURPS‘ use of half skill is simply a matter of making defenses play well: with their range flattened by the halving and the resulting too-low score boosted by the +3, the final defense scores are not too high, not too low, but just right for good game play.

And whether that captures the designers’ thoughts or not, it’s good enough for me! Defense rolls generally do play fine in GURPS. My FEND is a fun experiment, but there’s no pressing reason to toss out GURPS‘ rule for it or any other variant.

Still, I pondered the oddity of these half-skill rolls a bit more, out of some compulsion to explain them in a “See? The mechanism makes sense” manner, rather than as a break from normal rules that game balance demands. (Understand: there’s absolutely zero need to come up with such an explanation. I just wondered whether I could.)

Here’s the best I came up with:

The Parry or Block calculation is actually…

We could think of a Parry or a Block as actually two numbers combined and then divided by two – i.e., an average. Averaging is not a common mechanism in GURPS where skills are concerned, but it does pop up now and then. Taking the average of a skill and another skil, or a skill and something else, is an “official” mechanism that finds use in the game (if not at all frequently).

So, what is Parry or Block an average of? Try this: It’s the average of weapon skill and Perception (but with Per limited to Per 6).

Uh, why Per? It stands to reason that successfully defending against an attack requires first and foremost that you perceive it properly. Lousy perception would reasonably hurt defenses.

But why limit Perception to 6? Well, we can assume that Per 6 is the point at which you’re no longer struggling with the basic perception part of the equation. At Per 6 and higher, you perceive the fact of the attack just fine; from there, what matters are your reflexes (Combat Reflexes if you have it), your ability with the intercepting weapon or shield (i.e., your skill), and your general combat ability (also rolled into skill).

So, what does that get us? Let’s see: Your skill with a weapon is 14, and your Per is, oh, 10 or whatever. GURPS says your Parry or Block is 3 + (14/2) = 10. The above little redefinition says it’s the average of 14 and Per, but only up to Per 6 – so, (14+6)/2 = 10. Hey, same result! (Gosh, it’s almost like I planned it that way.)

Okay, yeah, that is wildly uninteresting. The above just nets you the same numbers as 3 + half skill. But with an exception: if Per is actually 5 or less, then you’ll end up with a lower defense score! Which kind of makes sense, for such a nearly sense-less combatant…

And what about Dodge?

Dodge uses its own unique calculation, one not based on any skill. But to line things up with the above, we could say that Dodge starts with (DX+HT)/2 – or Basic Speed x 2, if you prefer – and averages that with Per (max Per 6). Same result: you end up with a standard Dodge score (unless Per is super low, as above).


Changing the Per cap

Hmm. Imagine that you really like this idea of defenses being based partly on Per – so much that you’re disappointed to see the above make Per nearly irrelevant anyway (in that Per over 6 adds nothing). Try this:

Go ahead and cap Per at a higher amount – say, Per 10, or even Per 12. That makes Per matter over a greater range! But it also messes with typical defense scores: a weapon skill of 14 and Per 10 mean a Parry of (14+10)/2 = 12, higher than standard GURPS intends.

Fix those too-high scores by tacking a generic penalty onto all defenses, representing the inherent difficulty of defenses compared with other tasks (to make up an explanation on the spot). Set the penalty to -1 if Per is capped at Per 8, -2 if Per 10, -3 if Per 12, and so on (though I wouldn’t suggest going higher than that with the cap).

The result: The higher Per cap boosts defenses for any high-Per fighter, but the generic penalty reins that back in to a normal GURPS defense score. The catch: the higher the Per cap you set, the more you’ll decrease defense scores below the normal GURPS level for defenders with Per below the cap. Maybe you’ll like that effect, but test it wisely!

Using IQ instead

You could also play with using IQ instead of Per, if you want to inject raw smarts as a factor in combat defense. Say you defined Parry or Block as the average of skill and IQ, but capped at IQ 6. Again, this yields no difference from standard GURPS defense scores for just about any PC, or many of their foes. But unlike using Per, using IQ would lower defenses for the many low-IQ animals and monsters out there – by a lot if you then played with higher caps than 6, as above. Again, you’d have to test to check whether you really like that effect.

Or something else entirely?

If the use of PR or IQ doesn’t excite, what else might you average with weapon/shield skill as the calculation for Parry/Block? How about HT (appropriately capped, as above)? That injects these defenses with a bit of HT, which already forms part of Dodge.

Or, if you want to stick with something mind-related, how about Tactics skill (again, capped)? A character of modest IQ and no Tactics skill would have default Tactics even lower than a cap of 6, resulting in lowered defenses. This means you’ll want to learn some Tactics (or have a good IQ and Tactics default) for optimal defense. It’s an interesting idea – though using it means you’d have to start worrying about monster and animal Tactics skill, too, in order to calculate their defenses. 

What in tarnation is the point of this nonsense?

There’s none whatsoever. I’m not saying that injecting Per (or IQ) into defense scores is a better way to do things, or even a good one. Again, I was just wondering whether it’s possible to mentally re-define defense scores so their half-skill calculation appears more like something you might find elsewhere in the game, and less like a wholly one-off, proprietary mechanism used for defenses alone. The above is one way you could do so. That’s all.

If your reaction is, “Huh. What a complete waste of time,” well, I can understand that. Please ignore and move on.

But if your response is, “No, wait, this is a good thing. I can see the value in reassessing rules oddities like this, and I think I have another idea…”

… then please, seek professional help. I will, too. Together, we can find a cure for people like us.


  • Alex Koponen

    Without much thought…how about both attacker and defender roll their skill rolls. Attacker roll (how much roll is made by) minus defender roll gives a result. If positive (and Attacker did roll equal to or less than effective skill) then a hit, if equal then possible damage to wpn, shield or armor, if negative or Attacker missed skill on roll then a miss. Perhaps giving defender a bonus on their coming attack if attacker had missed and Defender had made their skill roll.
    Just a thought.

  • tbone

    So you’re suggesting a possible different way to run defenses? Sure, that can be fun stuff to play with. And, if I’m reading your idea correctly, it gets rid of “half skill” Parry and Block to begin with (which is an ideal I like for neatness, though whether it plays well is the issue. . . )

    But, unless I’m missing something: Is what you’re suggesting essentially a Quick Contest of skills to determine a hit? I know plenty of people have played with that idea – in fact, I think it was a suggested “making combat faster” option in Martial Arts for 3e. It raises some questions, such as how to handle Feints. But, in the end, while I haven’t ever tried it, I’m sure it’s worth experimenting with. (There are probably some blog or forum reports out there, by people who have tried running TH+defense as a Quick Contest.)

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