Bilateral contract/Unilateral contract

Japanese: 双務契約･片務契約 - そうむけいやくへんむけいやく

For example, in a sales contract, the seller is obligated to deliver an item, and the buyer is obligated to pay the price in return. A contract in which each party bears a debt that has a value for the other is called a bilateral contract. Whether or not something has a value as a consideration is determined subjectively by the parties, so no matter how low the price is, if the parties intend to sell or purchase, the price has a value as a consideration. All bilateral contracts are contracts for consideration. Among the contracts defined by the Civil Code, sales, exchange, lease, employment, contract, commission for compensation, deposit for compensation, partnership, and settlement are all bilateral contracts.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

たとえば，売買契約において売主は物を引き渡す義務を負い，買主はこれに対し代金支払義務を負うというように，契約の各当事者が互いに対価的な意味をもつ債務を負担する契約を双務契約という。対価たる意味を有するかどうかは当事者の主観で決められるから，代金がいくら安くても，当事者が売買のつもりなら，その代金は対価的な意味をもつ。双務契約はすべて有償契約である。民法が定める契約のうち，売買，交換，賃貸借，雇傭，請負，有償委任，有償寄託，組合，和解などは双務契約である。

出典　株式会社平凡社世界大百科事典第２版について　情報

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