Aristotle’s physical treatises. Arguments on behalf of a rotating earth were known to the
Medievals (e.g., Ptolemy himself, Jean Buridan [b. ca. 1300] and Nicole Oresme [b. ca.
1320/25]) but were not accepted as conclusive. Even in rejecting those arguments,
however, both Buridan and Oresme recognized that, on the assumption of a moving earth,
the heavenly phenomena would appear to us just as they do on the assumption of a
stationary earth.
This cosmology provided the theoretical basis for astrology. Actually, “astronomy”
and “astrology” were often used interchangeably; for example, Albert the Great (ca.
1200–1280) says there are two parts to astronomy, the second of which we would be
inclined to call “astrology.” In general, “astronomy 1” is the science of the stars, the
reasons for their relations to one another and to the earth; “astronomy 2” (astrology) is
the science of describing the position of the stars for obtaining “a knowledge of the
times.” The basis for the latter is the causal influences exercised by the former throughout
the concentric spheres of the universe down to the region under the moon. Astrological
judgments may seem to contradict human free will inasmuch as they seem to place in the
hands of the astrologer (astronomer) who understands the causal connection of the
movements of heavenly bodies to the events in the sublunar world, a knowledge of
necessity and determinism that appears to be at odds with human freedom. But the
apparent contradiction, Albert maintains, is not real. Astrological knowledge concerns
not human actions directly but dispositions to actions that are always subject to whether
the act will or will not actually be done. Persons remain masters of their fate by using
their intellect. A person can avert much evil from the effects of the operations of the stars
if he knows the influence to be exerted and can prepare to receive it. Choosing the
favorable hour expresses both the astrological influence and human freedom. On the
other hand, casting horoscopes, although not condemned by Albert, is recognized as
emphasizing the potential conflict between astrological horoscopes (as, e.g., when the
length of a life is predicted from the constellations) and free will.
As far as methods were concerned, Robert Grosseteste (b. ca. 1168) may serve as a
good example. Grosseteste based his approach to scientific knowledge on Aristotle’s
Posterior Analytics: a two-stage process. Beginning with an observed fact, the scientist
“resolves” the fact into the principles or elements that constitute it; the second stage
consists of “composing,” that is, reconstructing the fact on the basis of its “reasons” or
“causes.” This approach assumed both a uniformity in nature and a principle of economy
that chose between competing explanations on grounds of needing the fewer number of
suppositions. Because of these “extra-demonstrative” assumptions, Grosseteste’s
approach yielded probable rather than strictly scientific knowledge of the natural world,
since the observed facts would be deduced from more than one explanatory theory
without contradiction. In providing scientific knowledge of the heavens or of the
behavior of light in optics, Grosseteste recognized that he was providing the formal cause
(from the four-cause explanatory structure of explanation provided by Aristotle: formal,
material, efficient, and final causes), but he could not provide the material or efficient
causes—nor, within natural science—the final cause either. The formal cause could be
deduced mathematically (say, geometric epicycles and eccentrics in astronomy); but the
material and efficient causes required knowledge of natures—the subject matter of other,
higher sciences. Because of his metaphysical theory that light was the basic nature of
physical reality, Grosseteste regarded optics as the foundation of physical science; but
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