理論
りろん · riron · JLPT N1 · noun
theory
理 (reason, principle) + 論 (discussion, argument): a theory is reasoned argument about how things work.
理 means reason or principle, and 論 means debate or argument. Put together, 理論 is an argued system of principles. Read riron as 'ree-ron', like 'real iron' minus the 'al'.
理 — jade radical 玉/王 + village 里 (phonetic)
理 is a semantic-phonetic compound: the jade radical 王 (玉) on the left signals meaning, while 里 on the right gives the sound. It originally meant the natural veins or grain in a piece of jade, then extended to 'pattern,' 'order,' 'principle,' and finally the modern senses 'reason' and 'to manage.'