Sec.6.  A valuable consideration also is necessary to a valid contract.  A consideration is what is given or done, or to be given or done, as the cause or reason for which a person enters into an agreement.  Thus, the money given or offered, for which a man agrees to perform certain labor, is the consideration of the agreement.  So the money or other thing for which a promissory note is given, is the consideration.  A valuable consideration is any thing that is either a benefit to the party promising, or some trouble or injury to the party to whom the promise is made.

Sec.7.  Mutual promises are sufficient considerations to make a contract binding; but they must be made at the same time.  Such promises support each other.  The promise of one party constitutes a sufficient consideration for a promise by the other party.  In case the parties are distant from each other, if the proposition is made in writing and sent by mail, and a letter of acceptance is written and put in the mail, the contract is complete, unless, before mailing the letter of acceptance, a second letter has been received containing a retraction of the proposal.

Sec.8.  Promises which are wholly gratuitous are void; because, being neither a benefit to the promiser, nor an injury to the promisee, they are not regarded in law as a valuable consideration.  Hence, subscriptions to public works and charitable, literary, and religious institutions, if they are merely gratuitous, can not be collected, unless they have operated to induce others to advance money, make engagements, or do other acts to their own injury.

Sec.9.  As gratuitous promises are void for want of consideration, so merely gratuitous services, as voluntarily assisting to save property from fire, or securing beasts found straying, or paying another’s debts without request, afford no consideration upon which payment for their value can be lawfully claimed; there being no promise of compensation.  But if a person knowingly permits another to do certain work, as plowing his field, or hoeing his corn, although the work may have been commenced without his order or request, his consent will be regarded in law as an implied promise to pay for the value of the labor, unless the circumstances of the case are such as to forbid the presumption.

Sec.10.  A consideration must also be possible, and in accordance with law, sound policy, and good morals.  A contract founded upon an impossible consideration is void.  No man can be lawfully bound to do what is not in the power of man to do.  But it is otherwise, if the thing to be done is only at the time impossible in fact, but not impossible in its nature.  Hence, inability from sickness to fulfill an agreement, or the impossibility of procuring an article of a certain kind or quality which a person has agreed to deliver, would not exempt him from liability in damages for the non-performance of his contract.