Order page indicated the importance of distinguishing between perceiving the present and perceiving something as present.
We may perceive as present items that are past. Indeed, given the finite speed of the transmission of both light and sound
(and the finite speed of transmission of information from receptors to brain), it seems that we only ever perceive what is
past. However, this does not by itself tell us what it is to perceive something as present, rather than as past. Nor does
it explain the most striking feature of our experience as-of the present: that it is constantly changing. The passage (or
apparent passage) of time is its most striking feature, and any account of our perception of time must account for this aspect
of our experience.
Here is one attempt to do so. The first problem is to explain why our temporal experience
is limited in a way in which our spatial experience is not. We can perceive objects that stand in a variety of spatial relations
to us: near, far, to the left or right, up or down, etc. Our experience is not limited to the immediate vicinity (although
of course our experience is spatially limited to the extent that sufficiently distant objects are invisible to us). But, although
we perceive the past, we do not perceive it as past, but as present. Moreover, our experience does not only appear to be temporally
limited, it is so: we do not perceive the future, and we do not continue to perceive transient events long after information
from them reached our senses. Now, there is a very simple answer to the question why we do not perceive the future, and it
is a causal one. Briefly, causes always precede their effects; perception is a causal process, in that to perceive something
is to be causally affected by it; therefore we can only perceive earlier events, never later ones. So one temporal boundary
of our experience is explained; and what of the other?
There seems no logical reason why we should not directly
experience the distant past. We could appeal to the principle that there can be no action at a temporal distance, so that
something distantly past can only causally affect us via more proximate events. But this is inadequate justification. We can
only perceive a spatially distant tree by virtue of its effects on items in our vicinity (light reflected off the tree impinging
on our retinas), but this is not seen by those who espouse a direct realist theory of perception as incompatible with their
position. We still see the tree, they say, not some more immediate object. Perhaps then we should look for a different strategy,
such as the following one, which appeals to biological considerations. To be effective agents in the world, we must represent
accurately what is currently going on: to be constantly out of date in our beliefs while going about our activities would
be to face pretty immediate extinction. Now we are fortunate in that, although we only perceive the past it is, in most cases,
the very recent past, since the transmission of light and sound, though finite, is extremely rapid. Moreover, although things
change, they do so, again in most cases, at a rate that is vastly slower than the rate at which information from external
objects travels to us. So when we form beliefs about what is going on in the world, they are largely accurate ones. (See Butterfield
(1984) for a more detailed account along these lines.) But, incoming information having been registered, it needs to move
into the memory to make way for more up to date information. For, although things may change slowly relative to the speed
of light or of sound, they do change, and we cannot afford to be simultaneously processing conflicting information. So our
effectiveness as agents depends on our not continuing to experience a transient state of affairs (rather in the manner of
a slow motion film) once information from it has been absorbed. Evolution has ensured that we do not experience anything other
than the very recent past (except when we are looking at the heavens).
To perceive something as present is
simply to perceive it: we do not need to postulate some extra item in our experience that is the experience of presentness.
It follows that there can be no perception of pastness. In addition, if pastness were something we could perceive, then we
would perceive everything in this way, since every event is past by the time we perceive it. But even if we never perceive
anything as past (at the same time as perceiving the event in question) we could intelligibly talk more widely of the experience
of pastness: the experience we get when something comes to an end. And it has been suggested that memories-more specifically,
episodic memories, those of our experiences of past events-are accompanied by a feeling of pastness [see Russell (1921)].
The problem that this suggestion is supposed to solve is that an episodic memory is simply a memory of an event: it represents
the event simpliciter, rather than the fact that the event is past. So we need to postulate something else which alerts us
to the fact that the event remembered is past. An alternative account, and one which does not appeal to any phenomenological
aspects of memory, is that memories dispose us to form past-tensed beliefs, and is by virtue of this that they represent an
event as past.
We have, then, a supposed explanation for our experience of being located at a particular moment
in time, the (spacious) present. And as the content of that experience is constantly changing, so that position in time shifts.
But there is still a further puzzle. Change in our experience is not the same thing as experience of change. We want to know,
not just what it is to perceive one event after another, but also what it is to perceive an event as occurring after another.
Only then will we understand our experience of the passage of time.