理論・りろん;Riron(theory, as in science or "theory vs. practice") /

論理;ろんり;ronri (logic) (although the ALC examples seem to be only in a technical computer/math context)

・理屈;りくつ;rikutsu -"rational argument that makes sense"(the last kanji 屈 literally means "make someone yeild")

 - 合理 ごうり;/  gouri (rational OR reasonable (i.e. get up at a reasonable hour or a reasonable compromise - even if there is not math prroof involved) /