But we must now ask ourselves what we mean by "perceiving." Philonous maintains that, as
regards sensible things, their reality consists in their being perceived; but he does not tell us what
he means by perception. There is a theory, which he rejects, that perception is a relation between a
subject and a percept. Since he believed the ego to be a substance, he might well have adopted this
theory; however, he decided against it. For those who reject the notion of a substantial ego, this
theory is impossible. What, then, is meant by calling something a "percept"? Does it mean
anything more than that the something in question occurs? Can we turn Berkeley's dictum round,
and instead of saying that reality consists in being perceived, say that being perceived consists in
being real? However this may be, Berkeley holds it logically possible that there should be
unperceived things, since he holds that some real things, viz., spiritual substances, are
unperceived. And it seems obvious that, when we say that an event is perceived, we mean
something more than that it occurs.
What is this more? One obvious difference between perceived and unperceived events is that the
former, but not the latter, can be remembered. Is there any other difference?
Recollection is one of a whole genus of effects which are more or less peculiar to the phenomena
that we naturally call "mental." These effects are connected with habit. A burnt child fears the fire;
a burnt poker does not. The physiologist, however, deals with habit and kindred matters as a
characteristic of nervous tissue, and has no need to depart from a physicalist interpretation. In
physicalist language, we can say that an occurrence is "perceived" if it has effects of certain kinds;
in this sense we might almost say that a watercourse "perceives" the rain by which it is deepened,
and that a river valley is a "memory" of former downpours. Habit and memory, when described in
physicalist terms, are not wholly absent in dead matter; the difference, in this respect, between
living and dead matter, is only one of degree.
In this view, to say that an event is "perceived" is to say that it has effects of certain kinds, and
there is no reason, either logical or empirical, for supposing that all events have effects of these
kinds.
Theory of knowledge suggests a different standpoint. We start, here, not from finished science,
but from whatever knowledge is the ground for our belief in science. This is what Berkeley is
doing. Here it is not necessary, in advance, to define a "percept." The method, in outline, is as
follows. We collect the propositions that we feel we
-655-know without inference, and we find that most of these have to do with dated particular events.
These events we define as "percepts." Percepts, therefore, are those events that we know
without inference; or at least, to allow for memory, such events were at some time percepts. We
are then faced with the question: Can we, from our own percepts, infer any other events? Here
four positions are possible, of which the first three are forms of idealism.- (1) We may deny totally the validity of all inferences from my present percepts and
memories to other events. This view must be taken by any one who confines inference to
deduction. Any event, and any group of events, is logically capable of standing alone,
and therefore no group of events affords demonstrative proof of the existence of other
events. If, therefore, we confine inference to deduction, the known world is confined to
those events in our own biography that we perceive--or have perceived, if memory is
admitted.