III
Two other features of the role of analogy in early
Greek thought that are
especially notable are (1) their
use as a method of suggesting or
supporting explana-
tions of particular
natural phenomena, and (2) the
gradual exploration of the logic of analogy.
The begin-
nings of the first use go back to
the Milesians, who
based many of their accounts of obscure
astronomical,
meteorological, and geological phenomena on simple
analogies with familiar objects. Thus Anaximenes
compared lightning with
the flash made by an oar in
water, believing both phenomena to be the
result of
a cleaving process. His predecessor Anaximander sug-
gested a more elaborate and artificial
analogy in which
he pictured the heavenly bodies as wheels of fire
enclosed in mist; the stars themselves are seen through
openings in the
mist, and he described eclipses of the
sun and moon as being due to the
temporary blocking
of their apertures. Primitive though this theory is,
it
ranks as the first known attempt to construct a me-
chanical model of the heavenly bodies.
The use of such comparisons grows as the range of
problems investigated is
extended. Empedocles and
some of the Hippocratic writers, especially,
propose
ingenious analogies to explain processes that take place
within the body. Thus Empedocles compares the proc-
ess of respiration with the action of a clepsydra (water
clock).
De natura pueri compares the formation of
a
membrane round the seed in the womb with that of
a crust on bread as
it is baked, and De morbis IV
compares the
formation of stones in the bladder with
the smelting of iron ore. The same
writer also illustrates
how the humors travel between different parts of
the
body by referring to the way in which a system of
three or more
intercommunicating vessels may be filled
with a liquid or emptied by
filling or emptying one
of them, and on other occasions, too, Greek
scientists
refer to simple tests carried out on substances outside
the
body in their search for analogies for biological
processes.
These writers rarely examine explicitly the question
of how the analogies
they propose apply to the phe-
nomena they
were supposed to explain, and many of
their ideas seem farfetched. Even so, analogy provided
an
important, indeed in some cases the only, means
of bringing empirical
evidence to bear on obscure or
intractable problems, especially in such
fields as as-
tronomy and meteorology,
embryology and pathology,
where direct experimentation was generally out of
the
question.
Various writers, beginning with Anaxagoras at the
end of the fifth century,
refer to this use of analogy
under the general heading of making
“phenomena the
vision of things that are obscure”
(ὄψισ
τω̑ν
ἀδήλων
τὰ
φαινόμενα),
and awareness of most of the different
modes of analogy grows rapidly in
the fourth century.
Plato, himself one of the chief exponents of
reasoning
from analogy, was the first to point out how deceptive
similarities may be, and to draw attention to the differ-
ence between merely probable arguments, including
emotive images and myths, and demonstrations. Then
Aristotle analyzed
analogical argument as such in the
form of the paradigm, explaining its
relation to induc-
tion and showing that it is
not formally demonstrative.
Nevertheless he granted its usefulness as a
persuasive
argument in the field of rhetoric, and he even described
how a dialectician may exploit similarities in order to
deceive an
opponent. Plato and Aristotle made decisive
advances in exploring the logic
of arguments from
analogy: yet the effect of their work was not, of
course,
to preclude the use of such arguments, but rather to
show that
they are not formally valid. Moreover while
Aristotle successfully analyzed
analogy as a method of
inference, neither he nor any later Greek logician
made
much progress towards elucidating the other important
function of
analogy, namely as a method of discovery
in natural science.
