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in Greek philosophy and cosmology. Jaki stresses that Bishop Tempier’s decree
“expressed rather than produced that climate of thought.”
These statements of the teaching authority of the Church expressed an atmosphere in
which faith in God the Creator had penetrated the medieval culture and given rise to
philosophical consequences. The cosmos was seen as contingent in its existence and thus
dependent on a divine choice which called it into being; the universe is also contingent in
its nature and so God was free to create this particular form of world among an infinity of
other possibilities. Thus the cosmos cannot be a necessary form of existence, and so has
to be approached by a posteriori investigation. The universe is also rational, and
therefore a coherent discourse can be made about it. Indeed the contingency and
rationality of the cosmos are like two pillars supporting the Christian vision of the
cosmos.

The contingency of the universe obviates an a priori discourse about it, while its
rationality makes it accessible to the mind though only in an a posteriori manner…;
the rise of science needed the broad and persistent sharing by the whole population,
that is, an entire culture, of a very specific body of doctrines relating the universe to
a universal and absolute intelligibility embodied in the tenet about a personal God,
the Creator of all.
Jean Buridan was clearly imbued with the spirit of the tradition set by that decree of the
Bishop of Paris. He was professor of philosophy at the Sorbonne around 1330, and, as Jaki
notes, the first modern physicist. Buridan rejected the Aristotelian notion that the universe
and the motion of the stars were eternal; moreover, he stated that the motions of the
heavenly bodies were subject to the same laws as bodies on earth. In his impetus theory, a
moving body had impetus imparted to it by a source of motion. In Aristotelian physics, the
mover had to remain in continuous contact with the moved object; with Buridan this was
no longer the case, for, by virtue of an impetus imparted to it, the object moved off on its
own. The individual case was a small replica of the impetus which God imparted to the
heavens in the beginning of all motions. Buridan’s work prefigured Newton’s first law of
motion. Buridan’s great disciple Nicole Oresme (1323?–1382), later Bishop of Lisieux,
continued and made known the work of his teacher.
Within that climate of thought, it was possible for Oresme to treat with impressive
calm the possibility of the earth’s motion. Oresme’s unhesitating rejection of the
Aristotelian doctrine of eternal recurrence also reflects, to quote Jaki, “the robust
confidence of an overwhelmingly Christian ambience for which the once-and-for-all
process of cosmic existence was almost as natural a conviction as the air one breathed.”
Because the Middle Ages were steeped in the doctrine that the world had an absolute
beginning in time, there was an appreciation of the meaning of dynamic motion. The
process was not, of course, simple and straightforward, as Jaki is wont to note. In the
medieval tracts there was a great deal of mixing of “insights and rumours, of sound
principles and fantastic tales, of critical sense and baffling credulity, of reason and
magic.”
Duhem’s chief interest in medieval science had been that of a physicist looking for the
conceptual and historical sources of the basic form, the principle of virtual velocities, of
the true laws of motion. It remained for Jaki, in whom the physicist and historian of
physics is coupled with the theologian, to point insistently at the theological matrix of the

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