From the Beginning to Plato

FROM THE BEGINNING TO PLATO 149
Arguments against Change, Void and Motion
Melissus’ arguments against the possibility of any kind of change proceed
briskly but none too convincingly. First, qualitative change would imply lack of
internal homogeneity in the universe, since it would have to be qualitatively
different at different times. Next comes ‘change of kosmos’; apparently some more
essential type of change (change of internal structure?). The argument is that
such a change necessarily involves what has already been ruled out: e.g. increase
or partial perishing or qualitative change.
There follows the at first sight bizarre corollary that the universe does not
experience pain or mental distress; since pain and distress imply change or
inhomogeneity in various ways. To deny that would be pointless, unless the
universe were at least possibly a sentient being. If Melissus, like Parmenides,
began with the assumption that some mental activity occurred, that would for him
have the consequence that the universe has mental activity and so is sentient.
Next, there can be no such thing as void, which would be ‘nothing’ and
therefore does not exist. Hence there must be a plenum, which cannot admit
anything from outside into itself, and so there can be no movement, since nothing
can budge to make room for the moving thing. Two corollaries: first, no actual
dividing of the undivided universe is possible, since that implies movement.
Second, there can be no inner variation in respect of density, since ‘less dense’
can be understood only as meaning ‘having more void’.
The Relation to Ordinary Experience and the Attack on Sense
Perception
Where does Melissus’ monism leave common sense and sense perception? The
messages of sense perception cannot be true. Melissus bases his attack on the
fact that sense perception tells us that change occurs. The argument is: if
something is really so rather than so, it cannot cease to be true that this is so.
Hence, if our senses tell us that, e.g. this water is cold, and then that this water
has heated up, they would be contradicting themselves. So either our senses do
not really tell us anything; or there is no change, when again our senses have
misled us.
The aim is clear: it is to undermine any common-sense objections to the
positive doctrine about the universe. It therefore has to be an independent
argument. The central idea of this independent argument against change is that
nothing that is true can cease to be true, ‘for there is nothing stronger than what
is really so’. We need a conception of truth as unchanging; but then the
deliverances of sense perception need to be at least reinterpreted, for they give us
only time-bound truths. So we need to revise the common-sense notion that
sense perceptions are straightforwardly true.