(bound form) to judge between what is correct and what is incorrect; to criticize errors, specifically used in the context of the idiom 是是非非 shì​shì​fēi​fēi

(bound form) thoughts that go beyond logic or reality, specifically used in the context of the idiom 想入非非 xiǎng​rù​fēi​fēi

(bound form) difficult to understand; obscure or profound