It is also urged that a thing that tastes sweet when I am well may taste bitter when I am ill. Very
similar arguments are used about odours: since they are pleasant or unpleasant, "they cannot exist
in any but a perceiving substance or mind." Berkeley assumes, here and everywhere, that what
does not inhere in matter must inhere in a mental substance, and that nothing can be both mental
and material.
The argument in regard to sound is ad hominem. Hylas says that sounds are "really" motions in the
air, and Philonous retorts that motions can be seen or felt, not heard, so that "real" sounds are
unaudible. This is hardly a fair argument, since percepts of motion, according to Berkeley, are just
as subjective as other percepts. The motions that Hylas requires will have to be unperceived and
imperceptible. Nevertheless it is valid in so far as it points out that sound, as heard, cannot be
identified with the motions of air that physics regards as its cause.
Hylas, after abandoning secondary qualities, is not yet ready to abandon primary qualities, viz.
Extension, Figure, Solidity, Gravity, Motion, and Rest. The argument, naturally, concentrates on
extension and motion. If things have real sizes, says Philonous, the same thing cannot be of
different sizes at the same time, and yet it looks larger when we are near it than when we are far
off. And if motion is really in the object, how comes it that the same motion may seem fast to one
and slow to another? Such arguments must, I think, be allowed to prove the subjectivity of
perceived space. But this subjectivity is physical: it is equally true of a camera, and therefore does
not prove that shape is "mental." In the second Dialogue Philonous sums up the discussion, so far
as it has gone, in the words: "Besides spirits, all that we know or conceive are our own ideas." He
ought not, of course, to make an exception for spirits, since it is just as impossible to know spirit
as to know matter. The arguments, in fact, are almost identical in both cases.
Let us now try to state what positive conclusions we can reach as a result of the kind of argument
inaugurated by Berkeley.
Things as we know them are bundles of sensible qualities: a table, for example, consists of its
visual shape, its hardness, the noise it emits when rapped, and its smell (if any). These different
qualities have certain contiguities in experience, which lead common sense to regard them as
belonging to one "thing," but the concept of "thing" or "substance" adds nothing to the perceived
qualities, and is unnecessary. So far we are on firm ground.