Koichi's theory was not supported by anyone.
Koichi is learning leadership theories in order to become a good company president.
I’m bad at giving theoretical explanations.
You have reason behind your theory, making it a real theory (unlike those that don't have reason, I guess?).
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.