This is part of a multi-blog series on the basic and secondary attributes in GURPS. If you're new to the system, what are some things you'll want to think about? GURPS is point buy, so it's not up to the dice, but up to you and your point budget to determine your stats. Today we're lookin at the third of those stats - IQ - and its secondary traits - Will and Perception.
Also see posts on Gaming Ballistic, Ravens 'n' Pennies, and the GURPS 101 page.
How much IQ do you need?
IQ, like DX, is a multi-part attribute. In and of itself it is useful, but the secondary characteristics Will and Perception are directly derived from it. It's not cheap - 20/level - so your goal should be to determine how much you need based on your skills.
IQ provides your base for a large swath of mental skills - generally the ones that depend on knowledge (Science skills, Hidden Lore, Lockpicking in a realistic game, etc.) or mental acuity (Merchant, Fast-Talk) or both. It is also the base stat for spells, making it a critical element of a well-built mage.
To some degree you can avoid the need for a high IQ with Talents, which give pluses to skills over and above the base attribute. But for a generalist, or where you have too disparate a skill set, and/or you've maxed out your talent (this happens a lot with mages), you'll want a solid IQ.
GURPS also has a few places where you need to make straight IQ rolls. One particularly nasty example is mental stunning from Total Surprise (p. B393). You need to roll IQ to snap out of the shock of a completely surprising attack. Partial Surprise allows a cumulative bonus to snap out of it (since you're not totally unready for action), and Combat Reflexes can make the rolls trivially easy, but IQ is still a factor. You'll also need to make IQ rolls to avoid being fooled in combat, pull off a Ruse (Martial Arts, p. 00). IQ helps you unjam guns (p. B407), too. The list isn't exhaustive, but those are some examples of why it's useful to be smart - or at least, dangerous to be stupid, regardless of what kind of guy you're making.
In general, a good IQ is important, but plenty of folks get by with little or no additional IQ, simply through using Talents and specializing in non-mental skills. Per and Will are cheap enough on their own if you need a lot of them, and you can save 10 points by skipping out on IQ. But if you're going that route and expect combat, you will need Combat Reflexes to avoid standing around during surprise attacks.
Hey, I'm old-school, so the PC is just as smart as the player. In GURPS, this isn't entirely true. It's bad roleplaying to take IQ 7 and play your guy as a genius. But beyond that, GURPS is a skill-based system so how your guy executes his attempts is roll-based. A smart guy is going to succeed at brainy stuff more often - whether it is deciphering the code, picking the lock, spotting a Ruse, or snapping out of surprise. Like physical actions, GURPS leaves the decision of what to try up to the player but the success of execution up to the PC and the dice.
Now, on to the derived characteristics.
How much Perception?
Perception is what lets you see things, hear things, taste things, and otherwise sense things.
There are also a solid number of Per-based skills. Per-based Traps lets you spot traps. Survival is Per-based, because living in the wilderness is as much what you notice as what you know. Per-based skills like Search and Observation let you scope out the bad guys or find that stuff the smuggler hid so cleverly. Tracking is Per-based, too, and lets you follow folks like Aragorn does in the movies. Per is your defense against sneaky foes, too, as Per will let you see or hear intruders.
Perception also lets you hear invisible foes well enough to take a shot at them (or attempt a defense), see the ambushers so far out it's not an ambush so much as a partly-hidden defensive position, or smell the dangerous gas before it's too late.
Per is only 5/level, too.
So how much do you need? At 5/level it only takes two Per-based skills to make it worth increasing, and the flat bonus to sense checks that gives you is important. No outdoorsy type, sniper, or point man should be without a lot of Per.
Occasionally PCs will sell back some of their Per as a disadvantage - the Wizard template in Dungeon Fantasy 1: Adventurers does that. It's not a bad strategy if your character is meant to be brainy but not especially keen-sensed. But like selling back anything, you should be really certain you don't need it.
How much Will?
Will, like Per, is only 5/level. It is the basis of a few interesting skills, too - largely cinematic martial arts skills like Power Blow, or tough guy skills like Intimidation. If you want to be Chiun, you need a good Will score.
Will is critical for resisting a great many magical attacks and Psi powers. Will lets you shrug off exhaustion and keep going, or stay up late. It helps you resist hallucinations or drowsiness. It resists Influence rolls, and it is the score you roll against for Fright Checks. In a fantasy or sci-fi game with supernatural powers, you are going to be unhappy with a low Will score.
Like Per, you could sell back some Will as a disadvantage, but I've never personally seen in done in my games.
Will and the Rule of 16 - One important thing to know is the Rule of 16. Basically, the avoid "automatic victory over resistance" by getting extremely high Will-resisted attack spells, the Rule of 16 applies. Basically, the attack is capped at 16, or equal to the defender's score. So getting Will 16 makes the best chance of success against you from things like hostile spells a 50/50 prospect. Modifiers can hose you here, of course, but it's worth realizing that extremely high Will is effectively capped in utility, but so is the offense against you.
Overall, IQ is a good buy for anyone with a well-rounded set of mental skills. Will and Per are better purchases, alone or in conjunction with IQ, for folks with a more focused set of mental skills. Or for those who just need to spot things (scouts, guards) or shrug off influence and supernatural attack (everyone in a fantasy game.)