tured or was not "evolved in a refined community?" Or are
we to say that Austin derived his systematic ideas, not from
scientific study of English law, but from scientific study of Roman
law in a German university? Are we to say that we cannot "imagine
coherently" a system of law which enforces warranties indifferently
_ex contractu_ or _ex delicto_ as our law does, or which goes further
and applies the contract measure of damage _ex delicto_ as does the
law of Massachusetts? But enough of this. What we have here is not any
necessary distinction. It is rather what Austin calls a "pervading
notion," to be found generally in the systematic ideas of developed
legal systems by derivation from the Roman books. Roman law may have a
contractual conception of obligation _ex delicto_--thinking of the
delict as giving rise to a debt--and the common law a delictual
conception of liability upon contract--thinking in terms of recovery
of damages for the wrong of breaking a promise--without much
difference in the ultimate results. The fundamental things are not
tort and contract but justifiable assumptions as to the mode in which
one's fellow men will act in civilized society in many different
situations of which aggression and undertaking are but two common
types.

Returning to our second postulate of due care in affirmative courses
of conduct, we may note that in the society of today it is no less
fundamental than the postulate of no intentional aggression.
Aggression is the chief if not the only form of anti-social conduct in
a primitive society. Indeed, a Greek writer on law and politics of the
fifth century B. C. knew of no other subject of legal precepts. But
with the development of machinery and consequent increase in human
powers of action, the general security comes to be threatened quite as
much by the way in which one does things as by what he does.
Carelessness becomes a more frequent and more serious source of danger
to the general security than aggression. Hence a set of nominate
delicts requiring _dolus_ is supplemented by a theory of _culpa_.
Hence a set of nominate torts, characterized by intentional
aggression, is supplemented by liability for negligence, and the
latter becomes the more important source of legal liability in
practice.

Must we not recognize also a third postulate, namely, that men must
be able to assume that others, who keep things or maintain conditions
or employ agencies that are likely to get