Keeping Kings in Check 61A New Natural Law
Th e new natural- law perspective that arose in the high Middle Ages does
not have a widely recognized label. In the interest of a simple description, it
will be referred to as the rationalist approach. It was associated to a great
extent with the medieval discovery (or recovery) of the works of Aristotle.
Th is is evident from the fact that the Dominican Order of monks provided
the leadership in both of these areas— with Th omas Aquinas as the leading
fi gure. In fact, the two features of severe rationalism, coupled with the
dominant infl uence of Aristotle, became the hallmarks of medieval scholas-
ticism in its most developed form.
Aquinas, an Italian who lived in the thirteenth century, was actually a
transitional fi gure in that he acknowledged that the fundamental natural-
law obligation to do good and avoid evil was innate in humans. But the abil-
ity to draw conclusions from this core principle required the employment of
reason in a manner analogous to a geometrical demonstration. A crucial
feature of natural law in its rationalist guise was that it was altogether in de-
pen dent of the will or command of God. God himself was as powerless to
alter the truths of natural law as he was to play about with the truths of
mathematics. By the same token, natural law could not be the property
of any single culture, civilization, or religion— any more than the truths of
mathematics could be. Th is new rationalist approach became the dominant
tradition in natural law in the Middle Ages. As such, it exerted a powerful
infl uence on international legal thought.
Th e rationalist perspective entailed a rejection of the older animistic im-
age of natural law as a kind of biological instinct, in the manner proposed by
Ulpian. Natural law, in the new conception, was no more “written in the
hearts” of men than were the Elements of Euclid. Natural law, in other
words, was now seen as wholly external to the human frame— as transcen-
dental in character, rather than as innate. Its contents are accessible to hu-
mans on this view, but only by way of disciplined study and reasoning, not
as mere everyday common sense. Th is new kind of natural law was there-
fore, by necessity, in the distinctive custody of watchful scholars.
Th e rationalist version of natural law retained certain important features
of the older, organicist, stoic outlook. Th e most important of these was that,
like its pre de ces sor, it was not specifi c a l ly, or even pr i ma r i ly, about relat ions