How to say "Reason" in Japanese

When translating "reason" into Japanese, you must choose carefully between いわく and 所以. In Japanese, いわく (いわく (iwaku)) is typically associated with "reason, cause, history, legend (often with a negative connotation or mystery)" (Syllabus Level: N2) and represents Often used to introduce something mysterious, suspicious, or with a specific backstory. Can also mean 'according to...' when quoting someone, often with skepticism.. On the other hand, 所以 (ゆえん (yuen)) maps to "reason; cause; origin; source; the reason why..." (Syllabus Level: N1) and represents A formal and somewhat literary term. Often used in the pattern 「〜の所以」 or 「〜する所以」 to explain the fundamental reason, origin, or essence of something, implying 'the very reason why something is as it is'.. A literal translation of "reason" can often sound unnatural to native Japanese speakers if mixed up!