form was employed in the case of the concordat
of 1516 between Leo X. and Francis I. of France; a papal bull published
the concordat in the form of a concession by the pope, and it was
afterwards accepted and published by the king as law of the country. The
shades which distinguish these three forms are not without significance,
but they in no way detract from the contractual character of concordats.

Since concordats are contracts they give rise to that special mutual
obligation which results from every agreement freely entered into; for a
contract is binding on both parties to it. Concordats are undoubtedly
conventions of a particular nature. They may make certain concessions or
privileges once given without any corresponding obligation; they
constitute for a given country a special ecclesiastical law; and it is
thus that writers have sometimes spoken of concordats as privileges.
Again, it is quite certain that the spiritual matters upon which
concordats bear do not concern the two powers in the same manner and in
the same degree; and in this sense concordats are not perfectly equal
agreements. Finally, they do not assume the contracting parties to be
totally independent, i.e. regard is had to the existence of anterior
rights or duties. But with these reservations it must unhesitatingly be
said that concordats are bilateral or synallagmatic contracts, from
which results an equal mutual obligation for the two parties, who enter
into a juridical engagement towards each other. Latterly certain
Catholics have questioned this equality of the concordatory obligation,
and have aroused keen discussion. According to Maurice de Bonald (_Deux
questions sur le concordat de 1801_, Geneva, 1871), who exaggerates the
view of Cardinal Tarquini (_Instit. juris publ. eccl._, 1862 and 1868),
concordats would be pure privileges granted by the pope; the pope would
not be able to enter into agreements on spiritual matters or impose
restraints upon the power of his successors; and consequently he would
not bind himself in any juridical sense and would be able freely to
revoke concordats, just as the author of a privilege can withdraw it at
his pleasure. This exaggerated argument found a certain number of
supporters, several of whom nevertheless sensibly weakened it. But the
best canonists, from the Roman professor De Angelis (_Prael. juris
canon._ i. 106) onwards, and all jurists, have victoriously refuted this
theory, either by insisting o