There is a current debate proceeding about a perceived system of the background knowledge skills in relation to Active skills.
The GM and other players vaguely believe that a background skill can aid in the achievement of the Active skill. This is determined by rolling dice equal to the Background Knowledge skill associated with the Active skill and counting every two successes as success on the Active skill involved. (Much like the Centering skill in Metamagics)

I want to know if this is a valid SR3 rule.

By the SR3 background skills can be determined if the GM sees fit, to reflect the total of the active skill minus 3 points.
Example:
Active Skill: Sorcery 6
Knowledge: Magic Background 3 (Three points because it is 6 Sorcery minus 3 which equals 3 Magic Background.)

Casting a spell at Difficulty 4: rolls the Background dice which is 3 available, gets 2 successes that count as 1 success on the actual Sorcery test.

Then the Sorcery Test: Rolls the Sorcery dice(6) and some Spell Pool dice(2) and attains 3 success plus an additional success via the Background Knowledge tests success. Gaining the final net successes at 4.

You’re thinking of Complementary Skills, and they’re at GM’s discretion.

~J

What Kagetenshi said, plus I believe the BBB seriously discourages complimentary skills on any combat or magical skill (Except Aura Reading).

Dude… Centering can reduce TNs (by reducing TN modifiers, but still). Centering has complementary skills so whipped it isn’t even funny.

~J

Dude… Centering can reduce TNs (by reducing TN modifiers, but still). Centering has complementary skills so whipped it isn’t even funny.
[QUOTE]

You sound as if I had made an argument against Centering. I said that using Complimentory Knowledge skills would undermine Centering if used in conjuction with combat/spell skills.

What complimentary skills does Centering have?

Aaaah. I misunderstood that. I still disagree (not that I don't think complementary skills for combat wouldn't be a bad idea anyway), but I see your point now.

~J

A very good point. The above rule, by the way, counterbalances the fact that you get free Background skills.

~J

Oh, there? Yeah, that's because of the syntax for the form. I noticed that a while back. If you look at the autoquote function, it says something like "XYZZY, NPDG AM/PM"

~J

The only time I have ever seen complimentary skills used in combat, was our sniper wanted to stop a guy from running from us and he had a decent head start, and we didn't want him dead (no gel rounds on hand). So the player makes a called shot to make his leg unusable, before he rolls his attack he asks the GM if he can roll his anatomy knowledge skill as complimentary. GM adds a unknown modifier to the TN and lets it fly.

You're confusing Background skills with Knowledge skills. Seattle Club Background would let you know what clubs had been popular when and where they stood, not necessarily what goes on in them today.

~J

Really though, Knowledge and Background skills are really similar in that they usually don't directly effect game play like Active skills do. We tend to gray the line between Knowledge and Background skills atleast enough that they are helpful and useful, but not directly interacting with Active skills.

Background skills remind me of the older SR "Specilization Skills", while knowledge would be more "General" or "Concentration" like.

Actually background skills are just one of the sub-category of knowledge skills.