and eighteenth centuries no
distinction between natural obligations and civil obligations was
maintainable since all natural rights or obligations must for the very
reason that they were natural be legal also. If it was morally
obligatory that one adhere to a pact, then it must be treated as a
contract. However much systematized analytically, the Roman categories
of contract did not deal with undertakings from this standpoint. What
the jurists desired was not analytical categories but a principle upon
which men were to be held or not to be held upon their promises. Thus
the philosophy of contract, the principles underlying the binding
force of promises and agreements, became the chief problem of
philosophical jurisprudence of the seventeenth century, as interests
of personality were the chief subject of discussion in the eighteenth
century, and interests of substance, the philosophy of the law of
property, the chief subject of discussion in the nineteenth century.
The decisive element in seventeenth-century thought as to contract was
the idea of natural law; the idea of deduction from the nature of man
as a moral creature and of legal rules and legal institutions which
expressed this ideal of human nature. But the idea was put to work
upon existing materials and the result was a reciprocal influence of
the conception of enforcing promises as such because morally binding,
on the one hand, shaped to some extent by canon law and casuist
discussions of what promises were binding in conscience and when, and
the ideas of _nudum pactum_ and _causa debendi_ on the other hand.
Roman law was assumed to be embodied reason. As D'Aguesseau put it,
Rome was ruling by her reason, having ceased to rule by her authority.
Hence all consideration of the subject starts with the assumption that
there are morally naked agreements which for that reason are to be
naked legally. Where there was an exchange of promises there was the
authority of Justinian for enforcement (_synallagma_) and it was easy
to find a reason in the analogy of exchange of property. Where
something was exchanged for a promise, that something was a _causa
debendi_. But suppose there was no exchange of promises nor was
anything exchanged for the promise. There was nothing but a promise
assented to. In Roman law this would have to take the form of a
stipulation. In the Germanic law it would have required an oath or
the form of a real transaction of pledge or exchange. At co