Canonists and publicists do not agree about the nature of a
concordat and, consequently, vary much in the definition they
give. The various theories will be explained later, but for the
sake of orderly discussion at least a nominal definition will be
premised. In general, a concordat means an agreement, or union
of wills, on some matter. But as soon as we attempt to define
this general notion more clearly a difficulty arises. Agreement
of wills may be had in many ways: in friendship, in regard to
privileges, in a bilateral contract, etc. Prescinding for the
present from the exact nature of a concordat, and without giving
an exact definition, we may say that a concordat is a law,
ecclesiastical and civil, made for a certain country in regard
to matters which in some way concern both Church and State, a
law, moreover, possessing the force of a treaty entered into by
both the ecclesiastical and civil power and to a certain extent
binding upon both. The full meaning of the terms employed will
be explained below.