Putnam's Handy Law Book for the Layman by Bolles
An unpaid promissory note is an executory contract
Another classification is into express or implied contracts. An express contract is one actually made between two or more persons or parties; an implied contract is one that the law makes for the parties. Suppose a man worked a day for another at his request, and nothing was said about payment, the law would require him to pay a reasonable sum for his day's work. Another kind of contract technically called quasi contract differs somewhat from an implied contract and will be explained in another place.
To every contract there must be two or more parties, who have the legal right to make it. Not every person therefore who wishes to make a contract can legally do so. Of those whose ability to contract are limited are minors or infants. The period of infancy is fixed by law, and is therefore a conventional, yet needful regulation. In most states infancy ends at the age of twenty-one, though some states fix a younger period, eighteen for women. A person becomes of age at the beginning of the day before his twenty-first birthday. The reason for this rule is, the law does not divide a day into a shorter period or time except when this is required in judicial proceedings.
Insane and drunken persons also are under disability to make contracts. By the old law a drunken man who made a contract was still liable, and required to fulfill as a penalty for his conduct. A more humane rule now prevails and he can be relieved, though like a minor, if he wishes to avoid a contract, he must return the thing purchased, in other words he can take no advantage of his act to the injury of the other contracting party. If however he has given a negotiable note that has passed into the possession of an innocent third person, who did not know of his drunkenness at the time of making it, he can be held for its payment. It is not quite so easy to state rules that apply to insane persons because their conditions vary so greatly. A person may be insane in some directions and yet his insanity may not be of a kind affecting his capacity to make at least some kind of contracts. Again, he may have lucid intervals during which he is quite as capable of contracting as other persons. And again when an insane man has made a contract, the relief to which he is entitled depends on circumstances. In some cases he may repudiate it, a partial fulfillment only may be required.
The law has much to say about the consideration that is an element in every contract; in other words, there must be a cause, something to be gained by the parties in every contract to sustain it. If A should promise to give to B a house next week, and on the day fixed for transferring it A should change his mind, he could not be compelled to transfer it, for the promise would be without any consideration or thing coming from B. But if the house had been transferred, A could not afterwards repent of his act and demand its return. An executed gift therefore, free from all fraudulent surroundings, is valid: the donor of an executory gift is free to withhold its execution.