Theory
noun, suffix
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.
コウイチの理論はだれからも支持されませんでした。
Koichi's theory was not supported by anyone.
コウイチはよい会社の社長になるために、リーダーシップ理論を学んでいます。
Koichi is learning leadership theories in order to become a good company president.
理論的に説明するのは苦手です。
I’m bad at giving theoretical explanations.