I've always thought that it is a good idea to be fairly generous. If we remove augmentations from the mix, the EP skill system is set up in such a way that by just using one skill, it is very easy to fail. The complimentary skills are there to fill in the gap and make it possible for characters to be good in a field. So I'm leaning on the "fairly generous" side of the scale.

ThatWhichNeverWas wrote:

In general, I feel you should think about where you would use that skill on it's own, and see if that applies.

I second this. I woudn't add, say Profession: Aerospace Engineering when reparing a spacecraft in the field with Hardware: Spacecraft, but I would absolutley add Hardware: Spacecraft when designing a custom engine upgrade with Profession: Aerospace Engineering. I also wish Eclipse Phase had clearer guidelines for skill usage. The current system is absolutely fine, but a perfectionist in me wants more order.

My reasoning was that Hardware basically deals with maintaining stuff that already exists, while Aerospace Engineering as a profession is about creating new stuff, but you're probably right. This is what I'm talking about: between complimentary and/or overlapping Academics, Professions and Interests a lot of rolls require these small arbitary decisions. It can be fun, but also can be tiresome.

Well, when dealing with hardware, a good way to handle complementary skills (and this might apply in all cases, I'm just winging it on the hardware idea) would be to see if the higher-level academic knowledge applies directly to solving this problem. If it's purely academic/knowledge-based, then you'd just roll the Knowledge skill, and if your learning in this area doesn't practically apply to what you're doing, you just roll the Active, no bonus. So unless you're taking several minutes to actually plot the trajectory of the bullet and do all your math right, Academics: Physics does not apply to your Kinetic Weapons roll. So, for example, with Hardware: Aerospace, you'd roll it to properly apply patches to the hull of a ship, fix the sticky joint on a docking clamp or landing gear, or properly put all of space tab A into space slot B so your ultralight doesn't fall apart the instant you try to use it, without needing to check the manual. If, say, the magnets in your Metallic Hydrogen drive are out of alignment, and you need to fix this, because you're physically repairing it, you roll Hardware: Aerospace. But if you, say, have Professional training in Spacecraft Systems, or an advanced degree in Electrical Engineering, those might contain information you can directly apply to the problem and thus help fix your engine without accidentally melting anybody's face off. (On a metatextual level, it may be more appropriate and interesting to allow the most freedom for Complementary skills when a skill test is somehow narratively important, as opposed to a run of the mill "how well are you doing on front x" test. Seeing how much DUR your plane or shuttlecraft recovers in a dry dock while you fix it isn't excessively dramatic, even if it's something you'd value in-universe, while restarting your engines before you drift across the line for the Cordon and are evaporated by Interceptors is very dramatic, either way.)