In Roman law a mere agreement between two parties to give, do, or refrain from doing something was a nude pact (pactum nudum) which gave rise to no civil obligation, and no action lay to enforce it.
Not that the nude pact was considered to be destitute of all binding force; it gave rise to a natural obligation, and it might afford ground for a legal exception.
Moral theology, being the science of Christian conduct, could not be satisfied with the mere legal view of the effect of an agreement.
If the agreement had all other requisites for a valid contract, moral theology must necessarily consider it to be binding, even though it was a nude pact and could not be enforced in the courts of law.
In the Decretals of Gregory IX it is expressly laid down that pacts, however nude, must be kept, and that a strenuous endeavour must be made to put in execution what one has promised.
The Church fully admits and defends the right of the State to make laws for the temporal well-being of its citizens.
Others adopted the contrary opinion, and held that the want of formality only affected the external forum of civil law, and left intact the natural obligation arising from a contract.