After a sales contract is formed, it is up to the buyer to pay for their purchase. Payments usually occur in one of three ways: cash, credit, or a substitute for cash. It is the substitute for cash that requires negotiable instruments. Why is it important to have the option of a substitute for cash as payment in a contract? In what ways is a negotiable instrument a substitute for cash? In what ways is cash a superior form of payment? In what ways is a negotiable instrument a superior form of payment?