OBLIGATION OF CONTRACTS. By this expression, which is used in the constitution of the United States, is meant a legal and not merely a moral duty. 4 Wheat. 107. The obligation of contracts consists in the necessity under which a man finds himself to, do, or to refrain from doing something. This obligation consists generally both in foro legis and in foro conscientice, though it does at times exist in one of these only. It is certainly of the first, that in foro legis, which the framers of the constitution spoke, when they prohibited the passage of any law impairing the obligation of contract. 1 Harr. Lond. Rep. Lo. 161. See Impairing the obligation of contracts.