from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
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.