hip or conveyance, perhaps by calling the
people to witness so that there is an affront to the state if they
are called upon in vain.

When contact with Greek philosophers set the Roman jurists to thinking
about the basis of obligation, there were two sorts of promises: (1)
Formal promises, (a) by stipulation, using the sacramental word
_spondeo_ and thus assuming the pouring out of a libation that the
gods might take notice of the promise, (b) by public ceremony
apparently symbolizing a real transaction before the whole people, (c)
entered upon the household books of account, and (2) mere informal
promises not recognized by law. The latter depended wholly on the good
faith of the maker since the law had put down self-help which formerly
had been available to the promisee. Accordingly Roman jurists
distinguished civil obligations and natural obligations--those
recognized and secured legally and those which primarily had only a
moral efficacy. A _nudum pactum_ or mere agreement or mere promise,
not clothed with legal efficacy because it did not come within any of
the categories of legal transactions sanctioned by the _ius ciuile_,
created only a natural obligation. It was right and just to adhere to
such a pact, but only contracts, undertakings recognized by law
because of their form or nature, were enforceable.

With increasing pressure of the social interest in the security of
transactions through economic development and commercial expansion,
the natural-law philosophy slowly affected this simple scheme of
formal undertakings legally recognized and enforceable and informal
undertakings of only moral efficacy, and brought about the complicated
system of enforceable undertakings in the maturity of Roman law with
which you are familiar. Four features of this movement are noteworthy.
In the first place it led to a juristic theory of formal contract
which has affected our ideas ever since. In the strict law the source
of obligation was in the form itself. For in primitive thinking forms
have an intrinsic efficacy. It has often been pointed out that the
faith in legal forms belongs to the same order of thought as faith in
forms of incantation and that legal forms are frequently symbols to
be classed psychologically with the symbols of magic. The stage of
equity and natural law, relying on reason rather than on form,
governed by philosophy instead of by naive faith, looked for the
substance and found it in a pact preceding