1 The Birth of Science - MSRI

6.6 Postulates and the Meaning of “Mathematics” and “Physics” 167
¥), and who by virtue of their interests were called © 63
or © 64 — terms that can be partly transliterated as “physiologists”
or “physicists” but which meant simply “students of nature”. Aristotle,
whose works had a deep influence on medieval and modern terminology,
speaks specifically of physical science (© ). 65 He wrote a
work on this argument whose Latinized title, Physica, is the ancestor of
our contemporary word “physics”. But Aristotelian physics differs profoundly
from the homonymous modern science, both in subject matter (it page 214
encompassed not only plants and animals, but even the “prime mover”)
and in method.
Diogenes Laertius takes as generally accepted a division of philosophy
into three sectors: physical (which is to say natural), ethical and logical. 66
According to him, the division is due to the early Stoics. 67 Thus the term
“physics” corresponds to what came to be called “natural philosophy” in
the modern age.
Now, given that optical and astronomical phenomena, which were studied
by mathematicians, are themselves natural and so within the scope
of physicists or natural philosophers, in what way are the latter different
from mathematicians? This question, already considered by Aristotle, was
taken up again several times in Antiquity.
Geminus, for example, explains that it is not the business of optics (to
him a part of mathematics) to inquire into the actual direction of propagation
of rays, or the role played by air or ether in the transmission of light:
these matters are evidently within the realm of natural philosophy. 68
The most interesting passage available today about the relationship between
mathematical sciences and “physics” (natural philosophy) is also
by Geminus and we are able to read it because it made its way indirectly
into Simplicius’ commentary on Aristotle:
Alexander [of Aphrodisias] quotes . . . a passage from Geminus’ epitome
of his commentary on the Meteorologica of Posidonius. Geminus,
drawing from ideas of Aristotle, says: “It is characteristic of physical
science to consider what has to do with the substance of heavens
and celestial bodies, their powers and quality, their generation
and corruption . . . Astronomy, however, does not concern itself with
63 For instance, Diogenes Laertius says that Aristippus of Cyrene and Chrysippus called their
respective works on natural philosophers ©.
64 This term is often used by Aristotle, for example in the quotation of a statement of Anaxagoras
(Metaphysica, XII, 6, 1017b, 27).
65 See, for example, Metaphysica, VI, 1, 1025b, 19.
66 Diogenes Laertius, Vitae philosophorum, I, 18.
67 Diogenes Laertius, Vitae philosophorum, VII, 39.
68 Geminus, in [Heron: OO], vol. IV, 102, 19 – 104, 8.
Revision: 1.7 Date: 2002/09/14 23:17:37