Logiomancy

 Of all the possible terms for myself, I seem to have settled on logiomancer.

 A geomancer divines the future through the earth. A logiomancer divines the future through logic. The present, also. Not to mention the past. All things are subject to logic; or rather, logic is defined as the set of principles under which all things are subject. 

 To determine logic from fallacy, start with easy questions. Specific examples in the natural sciences. Learn the principles that consistently predict the future with regards to fire and heat, or gravity and falling, or distance and mathematics. Discipline these apprentice skills by applying them to more and more difficult problems. When discipline has been achieved, the logiomancer can trust their skills, and investigate otherwise unfalsifiable questions. Spiritual questions, as they are often called.