Source
Source (ulfir) is the cosmological concept in the Corps that underlies the practice of magic. Source is neither Coherence nor Unfolding, but rather, is conceptualized as an energy that underlies both Coherence and Unfolding as the user desires. It is stored in coherent patterns, and then is released to change the world. If Unfolding is always going on, and if it is influenced by human action, then Source is a way by which those skilled in its use create minor new folds in the universe. Source is not matter, but it is accessed through matter - e.g., through fos, whose consumption allows a user to tap the Source and use it to manipulate the world. It is generally acknowledged that fos is not the only means to access Source, however; for instance, sigillants can draw on stone in order to tap the Source, and various non-human creatures have magical powers that can only reasonably be explained as accessing Source in some way.