Consideration

   Consideration is the benefits and detriments by both parties in and agreement.  A detriments is something of value that a party gives up for something of benefit to them in return.  In order for a contract to be of legal value both parties must give up something of value in exchange for something that is of value to them.  In some cases the court may decide whether or not the two things being traded are worth the same value.  A promise does not bind a person to another person these are two completely separate things.  A promise could be changed since nothing of value has been exchange yet where as two things being traded is legally binding.  Somethings that make consideration of a contract legal are that consideration must involve a bargained-for exchange, must involve a trade of something of value, and the benefits and detriments that make up consideration must be legal.

Legality

   Legality is the final part of any contract.  It is also the part of the contract that can expose the real intentions of a party and what they plan on doing.  Legality is basically a proof reading over a contract. Its the part of the contract that checks to see if any of the laws have been violated as well as make sure that everything that has been agreed upon is in the contract.  A court will not help any parties that are in an illegal contract instead they will just leave them at the spot that they got themselves too.  This also means that neither party can enforce the agreement on each other.  The court may intervene if there is one party that is at less fault then other if it is getting back property or money.  For example if the offeror were to get one of his friends entered into a contract with him for selling guns on the black market this contract is no longer legal because they have just violated a law by selling arms illegally.

http://stevenclark.com.au/2009/11/09/contracts-101-part-3-the-six-elements/

Requirements of Capacity

   Capacity is the legal ability to enter into a contract.  This is also the assumption that the other party has the same capacity as they do.  There are some people who can get out of contract pretty easily like minors, people with some type of mental disorder, and those that are influenced by drugs.  A person who has a mental impairment can argue that they cannot be bound to the contract because of their disorder.  A person that has been diagnosed with a physical disorder can also do the same.  These types of people had to have had the impairment since birth or before they entered into the contract.  They must also be checked out by a      doctor who is qualified in that position.  Minors is a person who has yet to reach the age of adulthood.  Most minors can get out of most contracts because they are unknowledgeable, immature, or naive that they couldn't have known what they were doing.  A person could protect their self if they refused to enter into a contract with a minor or brought the minors parents into the contract.  Some minors are responsible for their actions because they have been emancipated or are legally not under the control of their parents.
   A person who has entered into a contract that is under the influence could argue that they were so out of it that they couldn't have possibly known what they were doing.  This decision is usually made by the jury whether or not the person can get out of the contract.  Some other people have limitations like convicts and aliens.  These type of people can get their rights taken away from them in times of war.  These people can also be denied things that are not of necessity.
   When a contract has been disaffirmed or proved that one party, usually a minor, cannot live up to expectations in a contract they must then return any goods that have been taken during the contract back to the other party.  Minors cannot pick which parts of a contract they want to disaffirm either.  An adult has no rights to get out of a contract just because they didn't know that the other party was an adult.  The minor usually cannot get out of a contract without compensating the other party first so as to protect the rights of the other party.
   When one party accepts a contract they have just ratified it or gone along with a contract even when they could get out of it.  An example would be if a minor turned to the age of an adult , usually 18, payed a payment on a car the he had bought when he was a minor he has just ratified the contract for paying when he was an adult.

Offers have Requirements

    The six elements form the heart of the contract, but each has individual branches on the details of that specific element.  An offer in order to be legal must have been made seriously, must be definite and certain, and have been communicated to the offeree.
Serious Intent
    If an offer is to be legal is must be made with the intentions of entering into a serious contract with another party.  An example would be if a person said to their friend "give me five dollars and its yours."  Course this couldn't be a contract because a person could not be force to sell their car for five dollars.  People sometimes get and offer and an invitations to negotiate messed up.  Invitation to negotiate is an invitation to deal, trade, or make an offer.  For example and advertisement in a catalog or magazine are usually invitations to negotiate not set offers.  If a person were to ask the store to buy the item at the sale price the person has now made and offer to the store to buy the item at sale price not regular price.  Often most price tags, signs in store windows, and prices on merchandise are all considered invitations to negotiate.
Definiteness and Certainty
    In order for a contract to be enforce the two parties must be definite and certain on what is to be exchanged.  For example if a fight broke out and one person broke a window and after the fight another person said that they would pay for a share of the cost of the window if the person who broke it planned on paying for the rest.  This contract could not be enforced because there was no certain amount of money that  was to be payed by either person.
Communication to the Offeree
   The offer must be communicated from the offerer to the offeree otherwise the contract isn't legal if one party cannot see the contract.  An offer can be communicated through telephone, letter, telegram, fax, e-mail, or any other way capable of communicating between the two parties.

The beginnings of a contract

    A contract is an agreement that can be enforced by law if it is legal.  There are three theories to a contract before a person should except a contract.  The first is the equality theory which states that both parties must be giving up something of value to each other.  The second is called the will theory which states that both parties had to accept the agreements made in the contract.  The third theory is called the formalist agreement which says that the parties had to actually meet and come to some form of agreement.
    There are six elements to every contract that a person can come across.  These six elements are offer, acceptance, genuine agreement, consideration, capacity, and legality.  An offer is a proposal by one party to another intending to create a legally binding agreement.  Acceptance is the second party's willingness to go along with the proposal.  Genuine agreement can be stated as a valid offer that has been agreed upon with valid acceptance.  Capacity is ones legal ability to enter into a contract on their own.  Consideration is the exchange of something of value between the two parties. The final part of a contract is legality.  Legality is the proof reading basically that checks to make sure the contract isn't breaking or violating any laws.