礼尚往来 is a four-character idiom formed by the sequential combination of 礼 (propriety), 尚 (to value), 往 (to go/give), and 来 (to come/receive), directly derived from the classical text "Book of Rites". Its literal construction positions 礼 as the subject, 尚 as the verb, and 往来 as the object, conveying the idea that propriety emphasizes reciprocal exchange.