Editing Unwritten: System Reference Document/Aspects and Fate Points (section)

==Unlocking Aspects in Play==

In addition to your character aspects, game aspects, and the situation aspects that the GM presents, you have the ability to create, discover, or gain access to other aspects as you play.

For the most part, you’ll use the Advantage action to make new aspects. When you describe the action that gives you an advantage, the context should tell you if it requires a new aspect or if it derives from an existing one. If you’re bringing a new circumstance into play—like throwing sand in someone’s eyes—you’re indicating that you need a new situation aspect. Questions from Discover actions can make aspects available as well.

With some skills, it’s going to make more sense to stick an advantage to an aspect that’s already on some other character’s sheet. In this case, the PC or NPC you’re targeting would provide active opposition to keep you from being able to use that aspect.

If you’re not looking for a free invocation, and you just think it’d make sense if there were a particular situation aspect in play, you don’t need to roll the dice—just suggest it. If the group thinks they’re interesting, write it down.