To some students of the law, contract law represents a mystery. The first and often biggest mystery is consideration. At one time, not too long ago, only contracts supported by a particular form of consideration were enforceable by courts because consideration served a functional or formal role in the creation of an enforceable contract.' Subsequently, consideration was accomplished through a very formalistic procedure requiring that some "thing" be transferred from one party to the other in exchange for another "thing." Determining whether consideration was present-in which case the contract is enforceable-in a dispute between two parties became the first and often most important question that courts addressed in contractual disputes. Did something physically move from one party to the other party that caused the other party to act (transfer something else in response), promise to act, or forbear from acting? Once consideration was proven, the contract was deemed enforceable and the court could address other issues such as breach and provide a remedy therefore. 

But, that was a while ago. As the consideration doctrine evolved, courts began enforcing agreements that were not supported by this formalistic version of consideration as long as the promises exchanged by and between the parties were "bargained for. " Or, to be more precise, consideration which was once viewed as an exchange of things-the items, goods, etc., that passed between the parties (in law school hypotheticals, always a "peppercorn" in exchange for something else) that caused the promise to be enforceable, became literally a "process" rather than a thing. The process that creates an enforceable contract between two parties occurs when the two parties make promises (bilateral4 as opposed to unilateral) and it is their individual intent that the promise be given or received in exchange for the other or return promise.

Alex M. Johnson Jr., The Legality of Contracts Governing the Disposition of Embryos: Unenforceable Intra-Family Agreements, 43 Southwestern Law Review, 191–252 (2013).