It was only after he mastered psychology, philosophy, history, spiritualism, prophesizing and religion, in his old age, that he knew his know he could be at peace. He mastered all these ____ (collective word).
The best fit I can think of fields but could mean anything really and is too generic. Sciences sounds better since he researched it from a fundamental point of view but history, prophesizing and religion are not sciences. It's not in school or academic, and spiritualism is not a subject, so subjects doesn't sound correct. Is there a better word for fields that sounds more high-brow?