From the Beginning to Plato

THE IONIANS 47
would fit much more comfortably with the theory Aristotle is reporting. 16 Flatearthism
more naturally presupposes the flat earth dynamics expressed in
Anaximenes’ theses (a) to (c). Second, Aristotle makes it clear that it was not
just Anaximander who subscribed to the indifference theory. On one guess only
the initial claim that the earth stays put because of ‘likeness’ reflects
Anaximander’s own formulation. Attention is often drawn to the probability that
Aristotle also has in mind a much later and no doubt more readily accessible
text, namely the account of the earth put in Socrates’ mouth at the end of Plato’s
Phaedo. Socrates is there made to claim that he has been convinced by ‘someone’:
presumably a tacit acknowledgement of a pre-Socratic source, although scholars
have never been able to agree on the likeliest candidate. The key sentences are
these:
Well, I have been persuaded first that, if it is in the middle of the heavens,
being round in shape, then it has no need of air to prevent it from falling,
nor of any other similar necessity. The likeness of the heaven itself to itself
everywhere and the equal balance of the earth itself are sufficient to hold it
fast. For something equally balanced, set in the middle of something all
alike, will be unable to tilt any more or any less in any direction, but being
all alike it will stay put untilted.
(Plato Phaedo 108e–109a)
Should we accept that Aristotle is mostly drawing on Plato, not Anaximander?
These arguments against ascribing the indifference theory—and with it
rejection of the dynamics of flat-earthism—to Anaximander are to be resisted. I
consider first the idea that Aristotle’s formulation of the theory derives largely
from the Phaedo text.
There are clearly similarities in language and thought between it and
Aristotle’s account of the indifference theory, notably the stress on ‘likeness’ as
a cause. There is equally a striking divergence. Plato makes the stability of the
earth a function of two things, its position at the centre of a spherical heaven and
its equilibrium in that position. Aristotle by contrast speaks only of the earth’s
position relative to the extremities, but makes what in Plato functions as an
indifference inference from equilibrium serve as the argument that it cannot
move position.
At first sight it may look as though the lack of fit between the two
formulations has no effect on the character or cogency of the reasoning, with
Aristotle simply extracting its essentials in economical fashion. There is in fact a
very significant difference.
Consider first the Platonic argument from equilibrium. This makes crucial
appeal to the weight of the earth. It supposes that a rigid body which is ‘like’—in
the sense that its weight is equally distributed throughout its mass—will stay put
in balance under certain conditions, namely if poised about a central fulcrum.
Then its weight on one side of the fulcrum will give it the same reason to tilt in