There is another method of payment similar to bill of exchange i.e., promissory note. In this method, in place of the seller drawing a bill of exchange on the purchaser, the purchaser himself makes a written promise to pay the amount to the seller. It is defined as an instrument in writing containing an unconditional promise, signed by the maker to pay on demand or at a fixed or determinable future time, a certain sum of money only to or to the order of a certain person or to the bearer of the instrument.