Fickle Sciences represent the use of esoteric knowledge that push the boundaries of what is thought possible. In fantasy settings we often call them magic, while in sci-fi settings we usually call them technology.
If you choose to use such mechanics, they differentiate from Approaches in scope: approaches cover things that could be normally done as established. For example, most people can yell at a bear, some might even scare it away. But not everyone can send it flying with a shout or communicate with it telepathically, at least not your average human.
Once there is a sense of what is internally consistent in your setting, Fickle Sciences can push those boundaries, or undo them altogether.
Fickle Sciences also allow for individuals to influence others, or create mechanisms of coercion, by allowing certain individuals to withhold knowledge that others can't access and, forming social systems around who gets to know what. Even if most or all can access these abilities, only a few might be able to actually understand its intricacies.
Whether Fickle Sciences are common place or knowledge that is hard to access makes a difference in how societies are formed and relations are maintained.
When creating a character, each character has a set of 6 Personal Words. Call them Power Words, Gadgetry, or something else appropriate. In science fantasy settings those might mean the same thing.
When bringing characters into a scene, offer 6 Location Words. Those might be resources, technologies, emotions, aesthetics, or something else. In case of doubt, pick about half of them related to the Place, and the other half related to a Theme.
Iara is a healer apprentice who knows these Personal Words: mend, soothe, find, bone, blood, sleep.
She arrives at the Grand Waterfalls, where the Local Words are: water, flow, fall, myst, ghost, cold
Using Fickle Sciences
When using their magic, technology, and any other science, a character chooses a pair of Words, one Personal and one Local.
Describe how these words combine to create an effect or provoke an outcome. Decide how it changes the environment, gives you an advantage, or empowers you to an impossible task.
You may make up to 3 pairs of Words and you cannot repeat a Personal Word. The more Words you use, the more specific, effective, and wondrous the effect created.
After that, roll 1d6. If you roll under the number of Words used at the time, cross out one of the Personal Words used and describe how you lost access to it, whether its magical conduit is broken, its device is defective, or something else.
You may choose instead to take a Condition and cross out a Local Word. Describe how you broke, tainted, distorted something, or made it inaccessible, dangerous, or forbidden, or something else.
Iara found someone hurt by a tree. She realizes a hunter was gravely wounded and is bleeding out, there is almost no pulse. She decides it is worth trying to save them, and begins an intricate procedure if healing.
She pairs Blood, and Flow, Find and Ghost, hoping to bring the hunter back to the world of living and guiding the blood to remain in their body.
Iara feels dizzy for a moment and realizes that in healing this hunter, her own spirit is being weakened. She must choose whether to give up some of her tools of practice (personal words), or let her spirit become ill by severing her ties with the environment (take a Condition and cross out a Local word).
Gaining and Recovering Personal Words
When you level up, choose whether you wish to recover a Word or gain a new one.
To recover a Word, roll 1d20. If your roll a number equal to or below the number of Words you still have, you may recover one you crossed out.
To gain a new Word, roll 1d20. If you roll over twice as many words as you know, including Words that are crossed out, you may gain a new Word.