and presupposed by the
formal ceremony. Thus a formal contract was a pact with the addition
of legal form. The pact was the substance of the transaction. The form
was a _causa ciuilis_ or legal reason for enforcing the pact. But if
the form was only a legal reason for enforcing something that got its
natural efficacy in another way, it followed that there might well be
other legal reasons for enforcement besides form. Consequently new
categories of contract were added to the old formal contracts and it
is significant that while the latter were transactions _stricti iuris_
the former were considered transactions _bonae fidei_ involving
liability to what good faith demanded in view of what had been done.
In the scope of their obligation these contracts responded exactly to
the postulate of civilized society that those with whom we deal will
act in good faith and will carry out their undertakings according to
the expectations of the community. On the other hand the old formal
contracts responded thereto in part only since their obligation was
one to do exactly what the terms of the form called for, no more and
no less. When one makes _nexum_, said the Twelve Tables, as he says
orally so be the law. New categories were added in successive strata,
as it were, and juristic science sought afterward to reduce them to
system and logical consistency. Thus real contracts, consensual
contracts and innominate contracts were added. But it is evident that
many of these are juristic rationalizings of what had been done for a
long time through formal transactions. Thus the consensual contract of
sale with its implied warranties rationalizes transfer by _traditio_
with stipulations for the price and for warranties. The real contract
of _depositum_ rationalizes _fiducia cum amico_. The real contract of
_mutuum_ rationalizes _pecunia credita_. But the latter was so
thoroughly established as a formal transaction that the case of a
loan of money, analytically a real contract, preserved the incidents
of the strict law. Moreover certain pacts, _pacta adiecta_, _pacta
praetoria_, became actionable which do not fit into the analytical
scheme of the Institutes. For example, a _causa_ or reason for
enforcing these pacts was found in their being incidental to something
else or in a pre-existing natural obligation which they undertook to
satisfy. There still remained natural obligations which had not been
given legal efficacy as the basis of actions