Consideration is merely the agreed price in a bargain. The price does not necessarily have to be money but it must have monetary value. For example, a bookseller promises to sell you the book and your consideration is the promise to pay the price. You could pay the equivalent of that price by providing a service to that value for example by cleaning the windows of the shop or by providing another commodity of that (or an agreed) value in exchange known as barter trade or counter trade. For example, fertilizer is frequently sold to Vietnam in exchange for rice or coffee to the same value as the fertilizer, instead of being bought in exchange for money. If a person promises to give you £100 as a gift at the end of the month, the promise would not be enforceable because it is a free gift. It has not been supported by a promise from you to do anything in return.