3. The parties to the agreement must be competent to contract.
Persons not able to contract are minors, lunatics, idiots and drunk people, and married women (except in some states in relation to their separate estates). The purpose of this arrangement is to protect those who cannot protect themselves. A minor may, however, enforce a contract if he chooses to do so. A contract with a minor for the necessaries of life, when they are not or cannot be furnished by a parent or guardian, is valid. And any contract ratified by a minor after coming of age is binding upon him. A person unable to contract personally cannot contract through an agent. But he may act as an agent.
4. The parties to the contract must assent to it.
The assent must be voluntary. It may be given by words, by acts, or by accepting the benefits of the offer. If acceptance is by letter, the contract is complete when the letter of acceptance is mailed. The parties must assent to the same thing. Assent imposing a new condition is no assent.
5. The promise must be for a consideration.
The law will not compel a person to give something for nothing. But the amount of the consideration is usually unimportant, so long as it is reasonable. Anything is a consideration which is of benefit to the person promising or of loss or inconvenience to the other. An illegal consideration is, however, not a consideration; nor is the performance of a moral duty, nor the doing of what would be a legal duty without the promise in question. If the consideration fails, the contract fails. One has no right to sue on a contract unless he has performed or offered to perform his part.
6. The contract must be made without fraud.
Fraud may be practiced in two ways, by making statements known to be false or by concealing facts that ought to be revealed. But if the parties meet on equal terms, with the same sources of information, and if nothing is done to conceal faults, there is no fraud in law. "Let the buyer beware," is an ancient maxim, and a buyer must exercise reasonable diligence and prudence. Fraud absolves the injured party, but the defrauding party may be held to the contract; that is, the contract is voidable at the option of the party deceived.
7. Some contracts must be in writing.
The principal classes of commercial contracts which must be in writing to be binding, are: (a) agreements for the sale of property of more than a certain value; (b) agreements of guaranty; (c) agreements not to be performed within a year.