There's really not that clean a distinction.
It is precisely that clean a distinction. From YS284, Thematic Thaumaturgy, which I have already cited in this thread:
All the types of thaumaturgy listed so far are divided along functional lines.
For reference, these are Summoning and Binding, Conjuration, Divination, Veils, Wards, Crafting, Transformation and Disruption, and Transportation and Worldwalking.
A thematic specialization looks at the subject matter in which all the various functions of thaumaturgy are applied--an ectomancer will be particularly effective with summoning, binding, divining, veiling, warding, crafting, transforming, disrupting, and transporting ghosts and other non-demonic spirits, for example.
...
The main thing the GM needs to watch out for here is ensuring that the theme is both strongly expressed and limited in scope; a theme which really amounts to "everything" in application is not theme at all--it's a cheat.
The list of suggested themes follows: Biomancy, Diabolism, Ectomancy, Entropomancy, Necromancy, Photomancy, and Psychomancy. Entropomancy covers the luck/fate theme discussed earlier. The list is explicitly not exhaustive, but the distinction between dividing thaumaturgy by function or by theme is perfectly clear, as is the reason for it: making sure that a given theme doesn't creep into "everythingmancy."
