expression, i-adjective
not without reason; reasonable; understandable
A formal, somewhat literary fixed expression meaning that something is not unreasonable or has a valid basis. Often used in the pattern 〜も故なしとしない to say that a situation or feeling is understandable.
彼が怒るのも故なしとしない。
It's not without reason that he gets angry; his anger is understandable.
この町が観光客に人気なのも故なしとしない。
It's not unreasonable that this town is popular with tourists.
もっとも is a common word for 'reasonable' or 'understandable' in everyday speech, while 故なしとしない is a formal, literary expression used in more structured contexts.
A fixed expression combining 故 (reason) + なし (without) + としない (not consider as). The exact historical derivation is uncertain, but it follows classical Japanese grammar patterns.