mmon law it
required delivery of a sealed instrument. Clearly there was no moral
efficacy inherent in these forms. Why should these "abstract" promises
be enforced and not others? Should every such promise be enforced or
should none be enforced without something in the way of exchange, or
should such promises be classified for the purpose of enforcement, and
if so, how?

Two theories arose in the seventeenth century. One may be called the
theory of an equivalent. This theory is obviously a rationalization of
the Germanic _causa debendi_ influenced by canon law and casuist
writings. According to this theory an abstract promise, no equivalent
having been given for it, is not naturally and hence is not legally
binding. Three reasons have been given for this which have figured in
juristic discussion of the subject ever since. It was said that one
who trusts another who makes a promise for no equivalent does so
rashly. He cannot ask to be secured in such an unfounded expectation.
This is too much in the spirit of the strict law. It denies any
interest except where the law secures it. It says that if the law does
not secure the interest, one is a fool to rely on the promise and so
has no interest. In like manner the strict law said that if one gave
his formal undertaking through fraud or mistake or coercion, he was a
fool or a coward and was not to be helped. But we cannot prove the
interest by the law. We must measure the law with reference to the
interest. Again it was said that if one promises without equivalent he
does so more from "ostentation" than from real intention and so an
equivalent shows that he acted from calculation and deliberately. It
is only deliberate promises that are morally binding, for only such
promises are relied upon by the prudent, upright man in his
intercourse with his neighbors. If this reason is sound, equivalent is
only a mode of proving deliberation and the real point should be that
the promise was made deliberately as something by which the maker
expected to be bound, not that the deliberation was evidenced in a
particular way by an equivalent. A third reason was that one who
parted with an equivalent in exchange for or in reliance on a promise
is injured in his substance if the promise is not kept. But if this is
the reason, the law should simply require restitution in case of
non-performance. If the interest involved is the deduction from
substance through rendering the equivalent, the obl