Abstracting Facets From Known Spells

Can a mage use his Sorcery skill to learn spell facets from the spells he already knows?

For example. My mage knows Falcon Skin, Fire Fan, Witch Key, and Wyrd Light. He would like to learn the spell facet for the Fire Element. Can he use his knowledge of Fire Fan to learn this facet?
Should he have to find other spells that also have the same facet before he could have enough examples of Fire Element to begin his studies?

How should this work?

MaBu pg174: “Variance is a chance to learn new facets…”, “Learning Facets If a book or scroll is found, facets may be learned in gameplay…”

As usual in Burning Wheel, something i.e. an Abstraction, must be risked and failed to progress. You use your existing spells to develop new abstractions. “Knowing” the facets of those spells as well would be double-dipping. How about lobbying your GM for an advantage die if you really must min/max?

The min/max misinterpretation aside, my question still stands. Are mages able to use their sorcery skill to disect the spells that they already know to attempt to learn the individual facets of those spells? Does spell knowledge impart facet knowledge of the spell or is it learned as a whole unit? And if the latter, could a sorcerer learn to disect it?

I don’t think that’s possible per the intent of BW magic. A spell is like Vichyssoise soup or orange paint. You can’t reconstruct the potato after it’s been through the blender and mixed with other ingredients, just like you can’t pull the red and yellow out of orange. However, you can add a new ingredient to both to make a new thing. Like blending in hot peppers into the soup to make spicy Vichyssoise.

As for a way to dissect them? Maybe… just maybe a really high Magic Theory-wise test made possible only with Aura-detecting abilities like Mage Sense? But even that might be limited to listing the facets that might make the spell. I still don’t think that would let you learn the facets, as it’s just theory. “Well, this soup tastes like potatoes, so that must be one ingredient. Hrm, and I detect a bit of heavy cream… and is that chives?” But again, knowing the ingredients used doesn’t allow you to make those ingredients from scratch.

The canonical answer is no. The ways to learn facets are detailed in the abstractions chapter.

So if a player wanted to burn up a mage that could learn to use the facets from the spells he knows he should either buy those facets in character burning, or write a belief about learning spell facets, perhaps seeking out specific tomes or masters in game to do so. (Using circles and wises to track them down and DoW to prove their worth, a compromise could become a task to test their worthiness).