The later fortunes of assumpsit can be briefly told. It introduced bilateral contracts, because a promise was a [288] detriment, and therefore a sufficient consideration for another promise. It supplanted debt, because the existence of the duty to pay was sufficient consideration for a promise to pay, or rather because, before a consideration was required, and as soon as assumpsit would lie for a nonfeasance, this action was used to avoid the defendant's wager of law. It vastly extended the number of actionable contracts, which had formerly been confined to debts and covenants, whereas nearly any promise could be sued in assumpsit; and it introduced a theory which has had great influence on modern law,--that all the liabilities of a bailee are founded on contract. /1/ Whether the prominence which was thus given to contract as the foundation of legal rights and duties had anything to do with the similar prominence which it soon acquired in political speculation, it is beyond my province to inquire. [289] LECTURE VIII. -- CONTRACT. II. ELEMENTS. THE general method to be pursued in the analysis of contract is the same as that already explained with regard to possession. Wherever the law gives special rights to one, or imposes special burdens on another, it does so on the ground that certain special facts are true of those individuals. In all such cases, therefore, there is a twofold task. First, to determine what are the facts to which the special consequences are attached; second, to ascertain the consequences. The first is the main field of legal argument. With regard to contracts the facts are not always the same. They may be that a certain person has signed, sealed, and delivered a writing of a certain purport. They may be that he has made an oral promise, and that the promisee has furnished him a consideration. The common element of all contracts might be said to be a promise, although even a promise was not necessary to a liability in debt as formerly understood. But as it will not be possible to discuss covenants further, and as consideration formed the main topic of the last Lecture, I will take up that first. Furthermore, as there is an historical difference between consideration in debt and in assumpsit, I shall confine myself to the latter, which is the later and more philosophical form. It is said that any benefit conferred by the promisee on the promisor, or any detriment incurred by the promisee, [290] may be a consideration. It is also thought that every consideration may be reduced to a case of the latter sort, using the word "detriment" in a somewhat broad sense.