Presentism
and Consciousness
Neil
McKinnon
Presentism draws you in. When you first become
acquainted with the presentist view of time it’s hard not to concur that this
is how time must be. What is it that makes the presentist theory of time so
compelling? Its appeal is often said to reside in the way that it illuminates
the temporal aspect of human experience. Psychologically, there is something
special about the present. All of our thoughts, feelings and actions occur
there. Past joys and hurts become less palpable and visit us more and more
infrequently as they recede into distant memory, while past visions and sounds
ebb into dullness and pallor. The future is more elusive and even less tangible
than the distant past. We often try to sniff it out, striving to locate it, yet
not for what it is, only for what it will be. But present awareness is fresh,
immediate, lustrous, and sometimes, exciting in a way that past awareness never
is. Given the psychological uniqueness of the present it is therefore tempting
to imbue this specialness with ontological import—to make this psychological
centrepoint a centrepoint of our metaphysics. The presentist does this, but not
merely by elevating the metaphysical status of present states of affairs above
all other temporal states of affairs. Rather, other temporal states of affairs
are ontologically excluded.
The primary aim of this paper is to present a
new difficulty for presentism. I will argue that, contrary to appearances, a
central feature of our psychology, namely conscious experience, embodies a
significant obstacle to presentism. I claim that this obstacle can be overcome
only if the presentist is willing to embrace some form of mind/body dualism.
And insofar as mind/body dualism is unattractive, so too is presentism.
Here are the two basic tenets of presentism:
(1)
Nothing that is past or future exists.
Accordingly, though we exist, neither our
deceased forebears nor our unconceived children exist.
(2)
There is change with respect to which facts characterise the world.
To illustrate this, consider my neighbour’s
dog, Conan. It once was a
characteristic of the world that Conan barked incessantly. It is at this very
moment a characteristic of the world that he is on an operating table somewhere
having his vocal cords severed. And it soon will
be a characteristic of the world that Conan is a non-barking animal (though he
will still probably move his jaws a lot). (2) is what makes presentism a tensed
theory of time: any metaphysically accurate survey of the world must be
formulated using the tenses, since it is these that convey how the world is, as
distinct from how it has been in the past
and how it will be in the future.
(1) and (2) set presentism apart from its main
rival, the tenseless theory. If the world has a history or a future then
according to the tenseless theory there are past and future entities as well as
present ones. Furthermore, there is one set of facts that eternally
characterises the world. Once we have described in full detail the various
entities in the world and set out the relations (including temporal ones) that
obtain between them, we have said all that there is to say about the world
‘once and for all’. That is the end of the story; no other set of facts did, nor
will, characterise the world. The denial of (2) makes the expression, ‘the
tenseless theory’ apt, since, according to the tenseless theorist, a
metaphysically accurate survey of the world is to be given without recourse to
tenses.
Where does the attraction of presentism lie?
The psychological privilegedness of the present has already been noted. There
are routes to presentism from this psychological privilege. A simple route is
to claim that presentness is a phenomenal property; we can directly apprehend
that our experiences have the monadic property of presentness. However, the
view that there is a property of
presentness is not shared by most presentists.[1]
A related, but less crude, path to presentism
flows from more theoretical considerations. There appears to be a powerful case
for presentism if it can be shown that certain aspects of our psychology could
not be properly explained if presentism were false. Over the course of our
lives we have a great number of experiences. Yet, if the tenseless theory of
time is correct, all of these experiences are ontologically on a par. If none
of our experiences are ontologically privileged, then why are they not
psychologically on a par? Why do we discriminate phenomenally against past and
future experiences? [Ferré 1972: 435–6.]
And if there is no change of the facts that characterise the world, then
how do we explain the unease which rises up in us as we anticipate an
unpleasant event that is inexorably approaching us, and the wonderful sense of
relief that accompanies its ending? [Prior 1959]
It might be argued that these considerations do
not lead directly to presentism. There are other tensed theories of time which
ontologically privilege the present, but not by ontologically excluding the
past, or in some cases, even the future. Such theories treat presentness as a
special transient intrinsic property. Elsewhere, I have argued that despite
appearances such theories don’t mark any advance over the tenseless theory when
it comes to addressing these considerations [McKinnon 1999].
Other reasons have been given for embracing
presentism which are not so closely tied to psychological matters. Sometimes,
for example, it is thought that only presentism affords us with an adequate
response to McTaggart’s Paradox [Christensen: 1974].
I will not mention any further motivations for
presentism, as it is not my purpose here to be exhaustive in this regard. I
have emphasised in particular those motivations arising in connection with our
phenomenal experience, because, as I will explain later, issues surrounding the
metaphysical basis of consciousness actually turn out to yield considerable
negative consequences for the presentist.
Having briefly introduced presentism and some
motivations for that view, I turn next to some further relevant details
concerning the metaphysics of presentism.
It is often noted that the words ‘now’ and
‘present’ have no fixed usage in everyday discourse. Sometimes, it seems that
they are meant to indicate a very brief span, as in the following example:
Jamie stares listlessly from his rumbling
carriage. The monotony of the lifeless desert sands remains, as it has for the
last several hours, unrelieved. Wrenching his gaze from the window, he attends
to his shoes. Just now, an amusement park hurtles by.
In other situations they might be used to
encompass longer periods. Consider a commander speaking to his troops on the
eve of a pivotal battle: ‘Now is our last chance to repel the enemy’, he says
as he exhorts them to one last effort. Evidently, he does not intend his use of
‘now’ to be as temporally restricted as its use in the previous example. In
this context, ‘now’ suggests a period extending from the time of utterance
until the result of the battle is beyond doubt.
Granting the apparent context-dependent nature
of ‘present’ and ‘now’ as they feature in ordinary discourse, we might be
curious about how the presentist uses these words. When the presentist says
that the only temporal items in existence are present ones, what does this
amount to?
While doing metaphysics, the presentist’s sense
of ‘present’ is not one whose temporal extent varies according to context. If
it were, then what exists could vary from context to context. I take it that
the presentist prefers not to conclude that we can talk things in and out of
existence merely by shifting contexts. So, the presentist must have in mind a
special, fixed sense of the present—the metaphysical
present, if you like. What, then, is the scope of the metaphysical present?
Surely it is not so broad as to include the Age of the Dinosaurs, the Big Bang
and the extinction of our sun. This would be to make presentism too much akin
to the tenseless theory of time. Just how narrow must it be?
It is often thought that the presentist should
conclude that the metaphysical present has no scope; that figuratively
speaking, it is a knife-edge separating what has been from what is yet to come.
In other words, the metaphysical present is temporally unextended. The
justification for this view traces back to Saint Augustine [Augustine 1991:
232]. Here is what I take to be the essence of Augustine’s influential
argument. If the present is extended then it has wholly distinct parts and
those parts must be simultaneous. This rests on the assumption that if x and y are both metaphysically present then they are simultaneous. On
the other hand, if the present is extended then it also seems that its disjoint
parts cannot be simultaneous: if x
and y are not temporally overlapping
then they are temporally separated and hence, not simultaneous. Thus, we have a
reductio of the view that the
metaphysical present is extended.
If Augustine is to be believed, the presentist
must regard the present as temporally unextended. I have some reservations
about whether Augustine’s argument licenses this conclusion (see §10), but I
will put these aside for now; as far as I know, no presentist has suggested in
print that the present is durational. As we will soon see, the metaphysical
nature of consciousness leads to problems for the view that the metaphysical
present is unextended. It turns out that there are reasons for thinking that
conscious experience is always temporally extended.
On the hypothesis that the metaphysical present
is durationless it follows that any conscious experience we are having must
itself have no metaphysical duration. But do we really have durationless
conscious states? At this point, it is important to eliminate a possible source
of confusion about this question. I will now outline an unsatisfactory, but
instructive, argument against presentism. Isolating the flaw in this argument
will help us to remain clear about what is at stake.
Echoing Kant, William James observes that there
is a significant difference between a mere succession of awarenesses and an
awareness of succession [James 1981: 591]. To illustrate this point, suppose
that we have a series of awarenesses. Further suppose that each of these
awarenesses is a phenomenal island, untinged by vestiges of past awareness. In
that case, we would not have any conception of one thing following another, and
hence, we would have no conception of change. So what is required for us to
have a conception of succession, and therefore, of change? Here, James quotes
Volkmann with approval:
…if A and B are to be represented as occurring in succession they must be simultaneously represented; if we are to
think of them as one after the other,
we must think them both at once [James 1981: 592].
Thus, for two states of affairs to be
represented to us as occurring successively, the first must leave a trace
behind, so that when we become aware of the second, this awareness of the
second is juxtaposed with an awareness of the first. Thus, James thinks that
the span of our phenomenal present is
far from being a vanishing point. In his opinion, the breadth of this present
can be anywhere from a few seconds to a minute [James 1981: 603].
Suppose that James is right. The mistaken
argument against presentism concludes that since our phenomenal present has
temporal breadth, so too does the metaphysical present. The problem with this
argument is that it conflates the distinction between content and its bearer. A
written token of ‘loud’ represents loudness, but the bearer of this content is
not itself loud. In the case that interests us, even if we think that the content of our phenomenal present
represents past and present things as co-existing, it remains an open question
whether our phenomenal present qua bearer
of this content has metaphysical extension. The presentist can claim that the
bearer is metaphysically durationless. To make things uncomfortable for
presentists, it must be argued that the bearers
of conscious states have temporal extension. It is to this task that I now
turn.
In this section, I will discuss prima facie reasons for thinking that
the neural correlates of consciousness, namely, those neural phenomena which
are direct correlates of consciousness, are temporally extended. Later, I will
discuss what implications this might have for consciousness itself. To help locate the ensuing
discussion, a very brief overview of the cerebral cortex is worthwhile, since
this is where the neural correlates of consciousness are most likely to be
found.[2]
Two separate sheets of nerve cells, one on each
side of the brain’s exterior, make up the cerebral cortex. The surface area of
these sheets is sufficiently large that they must be folded to fit inside the
skull. This folding accounts for the brain’s characteristic walnut-like
appearance. Functionally speaking, the cortex is strikingly modular. There are
separate regions devoted to processing information from each of the sensory
modalities, namely, sight, touch, smell, taste and hearing. Moreover, at least
some of these regions are also modular. For instance, specific visual functions
have been assigned to more than twenty cortical areas. There are separate
regions devoted to handling colour, shape, contrast, orientation and movement.
As Singer puts it:
Depending on the features
constituting the object (of perception), neurons become activated in different,
often noncontiguous cortical areas, and it can be predicted that even simple
visual patterns will give rise to simultaneous responses in a vast number of
(widely distributed) neurons [Singer 1994: 80].[3]
The brain itself is composed of billions of
interconnected nerve cells, or neurons, and information is carried and
disseminated throughout the brain by these cells. Each neuron has a protruding
fibre called an axon, whose firing
transmits information to adjoining neurons. It also has other fibres called dendrites, which receive information
from the firing of adjoining neurons. The neural correlates of consciousness
are those neuronal activities that are directly correlated with consciousness.
Of special interest to us is the way in which neurons encode information. It
turns out that much of this coding is temporal as well as spatial, as I will now
explain.
It has been known since the 1920s that at
peripheral levels of sensory systems single neurons represent fixed stimuli;
the firing of a given peripheral neuron always codes for the same sort of
sensory stimulus [Adrian and Zotterman 1926]. The intensity of that stimulus is
registered by the average firing rate of that neuron over a brief period of
time; the stronger the stimulus, the higher the firing rate. It is not,
however, plausible to think that all, or indeed, many, representations at higher
levels of processing, such as those which correlate with conscious states, are
signalled exclusively by one neuron. A single-cell code precludes
generalisation from old representations to new ones. This is a severe problem,
since the system will hardly ever be presented with exactly the same
stimulation on multiple occasions [Fotheringhame and Young, 1997: 49]. There is
also a combinatorial problem. Even if we restrict ourselves to visual
stimulation, it is unlikely that there would be enough neurons in the brain ‘if
all distinguishable objects, including their many different views, each had to
be represented by a specialized neuron...’ (Singer, 1994, pp. 80–1). Thus, it
is likely that higher-level representations embody assemblies of co-active
neurons.
Although it is unlikely that the brain employs
single-neuron codes on a large scale, important roles have commonly been
assigned to coding by firing rate (rate coding) at all levels of processing. It
has, for instance, been widely held that colour and form are represented by
rate codes [Burkhalter and van Essen 1986]; [Hubel and Livingstone 1987], and
that the perception of motion is rate encoded [Koch and Crick 1994: 98].
Moreover, evidence has been growing to suggest
that coding in the temporal domain is not restricted to codes of average firing
rate. Two neurons sharing the same average firing rate over a certain period of
time might have firing patterns that differ markedly when considered in fine
detail. In a rate code these differences are regarded as noise, contributing
nothing to the information content of the code. However, it is plain that in
principle, at least, these differences in the temporal relationships between
individual firings could constitute differences in information content. Let us call
this potential means of coding timing
coding. Evidence for the timing coding of contrast (e.g. the contrast
between figure and background) has been presented in [Richmond 1997] and
[Mechter et al. 1998].
It appears that there are good reasons for
thinking that the neural correlates of many conscious states are temporally
extended. So we can conclude that many conscious states are themselves
temporally extended. Yet, the presentist says that the metaphysical present lacks
temporal extension. Therefore, we can conclude that presentism lacks the
ontological resources to adequately support consciousness. And since it is
clear that there are conscious states, it can be concluded that presentism is
falsified.
This is a pleasingly simple argument, but it is
much too eager to reach its conclusion. One response might be to observe that
the neural correlates of consciousness are just that, namely, correlates of consciousness. We need a
bridging argument to justify the conclusion that conscious states themselves
have temporal extension. An example would be an argument for some form of
mind/body identity theory. However, this would not be a dialectically useful
response, since it concedes that something
has temporal extension, namely, the neural correlates of consciousness; that
concession alone is enough to cause problems for presentism.
A better response is to note that presentists
admit certain analogues of temporal extension which might be capable of
standing proxy for the concrete temporal extension favoured by tenseless
theorists. The thought is that these resources might allow the presentist to do
justice to the temporal features of the neural correlates of consciousness
without conceding that anything has temporal extension. Thus, much still needs
to be done to show that presentism is in trouble. I will first argue that if an
identity theory of mind/body is correct, then presentism does not in fact have
the resources to plausibly account for consciousness. I will then consider what
prospects there are for presentism in the absence of an identity theory.
First, I will make a few amplifying remarks
about identity theories of mind. Those who favour physicalism generally prefer
some sort of identity theory. Old-style physicalists preferred a type identity
theory, where a certain type of mental state is identified with a type of
physical state.[4]
This seemed a little severe since it meant that organisms with physiologies
different from humans could not share the same sorts of mental states. The
intuition that a certain mental state could be realised in different ways led
to functionalism. According to functionalists, a mental state is defined in
terms of its functional relationships with the outside world and with other
mental states. Sometimes, this leads to a token identity theory, where
particular tokens of mental states are to be identified with particular tokens
of physical states, but no type identities obtain.[5] Sometimes it
leads to the identification of particular mental states not with their physical
realisers, but with functional role states. On this view, mental states are not
identical with the physical states that realise them, but are nevertheless constituted by physical states. What I
say about the temporal properties of conscious states according to the identity
theory carries over to this view, since the spatio-temporal properties of
mental states on this view are coextensive with the spatio-temporal properties
of their realisers.
Now, consider the following example. Suppose
that you are reclining outside on a beautiful summer’s day with the Sunday
paper beside you. You gaze sleepily out at the clear blue sky. The neural
correlates of your colour-experience involve either rate or timing codes. Either
way, the neural correlates of this experience seem to be temporally extended.
On the assumption of an identity theory, the conscious state is itself
temporally extended. The tenseless theory of time accommodates this fact quite
easily. Your experience is spread out in time; its earliest part is no less
existent than its latest part. Presentists have to say something different,
since they say that the metaphysical present is unextended. We will now see how
presentists might try to do without temporal extension.
Since presentists hold that nothing past or
future exists, they generally construe facts ostensibly about past and future
entities as disguised facts about existing things. Some facts about putative
past or future states of affairs, for instance, can be expressed purely in
terms of entities that were or will be constituents of those states of affairs.
John Major’s having been Prime Minister of the United Kingdom, for instance,
can be expressed in terms of a certain relationship between John Major and the
property of being Prime Minister of the United Kingdom. John Major has the
property of having instantiated the
property of being Prime Minister of the United Kingdom. Other ostensibly past
and future states of affairs are not so easily accommodated. Consider the
past-tensed state of affairs of the horse Phar Lap’s having been a Melbourne
Cup champion. Phar Lap no longer exists according to the presentist, so
something else that does exist has to be found to act as a place-holder for
him. There are a few things we could try here. We could say that the fact that
Phar Lap was Melbourne Cup Champion is really a fact about his stuffed hide,
now residing in the Melbourne Museum, which was once the skin of a horse that
won the Melbourne Cup. Or we could say that it is really a fact about Phar
Lap’s haecceity, which was once instantiated by a horse that won the Melbourne
Cup. We could even say that it is a fact about the world as a whole that it
once contained a horse which won the Melbourne Cup.[6]
How could this sort of presentist handle the
case of your blue sky experience? To simplify things, let’s pretend that your
blue sky experience consists in the firing rate of a single neuron over a
certain period of time. Since in this case the neuron which supports this
experience still exists, there is no need to invoke recondite entities like
haecceities or world-properties. The neuron itself has various past (and
perhaps even future) tensed properties like having fired a certain time ago, a
certain time ago before that, and so on. On this view, the conscious state
consists in the instantiation by the neuron of a conglomerate of past, and
perhaps future, tensed properties, along with how it is in the present. So the
conscious experience is largely composed of non present-tensed states of
affairs about how the neuron was or will be. On the face of it, this is very
peculiar. We are asked to believe that a present conscious state could be composed mostly by facts about what no longer obtains, or what does not yet
obtain.
Even worse, it seems to allow that a conscious
experience could be made up entirely
of past or future-tensed facts. After a neuron fires, there is always an
interval during which it is not firing. Consider some moment, in the middle of
a sequence of firings that constitute your blue sky experience, when the neuron
is not firing. Do we say that you are having your experience at that moment? If
we say yes, then that experience is composed entirely of non present-tensed
states of affairs about the firing of the neuron. Can we say no? It’s hard to
see how. If we say no, then we are saying that you can have the blue sky
experience only while the neuron is firing. But this seems unjustified. A
single firing of a neuron makes no significant difference to the average firing
rate of the neuron, and it is this average firing rate which constitutes my
experience. So it is hard to see why the matter of whether the neuron is
currently firing or not should make any difference to whether or not you are
having the experience. Thus, it seems that the presentist has no good reason
for denying that conscious experience could involve only non present-tensed
facts.
Note also that the problem of conscious states
being composed by past (or future) tensed states of affairs is not merely one
of peculiarity. Past tensed states of affairs cannot be constituents of present
tensed states of affairs like your blue sky experience because they lack the
right structure. The present tensed state of affairs that the neuron is in a
firing state registers a fact about how the neuron is. However, a past tensed state of affairs to the effect that the
neuron was in a firing state two seconds ago is a fact purely about what
happened two seconds ago. It conveys only that two seconds ago the property of
being in a firing state was instantiated by the neuron. And this is not the
right kind of structure to be a constituent of fully-fledged present tensed
states of affairs like your blue sky experience. Here, it is useful to compare
past-tensed states of affairs to modal states of affairs. For the same sorts of
reasons we would not like to think that a fully-fledged existing entity could
be composed mostly by states of affairs about what is merely possible. So, for
instance, we would not be happy to think of my blue sky experience as being
composed mostly by states of affairs about what is merely possible for the
neuron.
It is worth mentioning that not all presentists
think that past or future tensed facts need to be facts about something that
now exists. In the tradition of Meinong, some presentists have held that
non-existent entities possess properties and stand in relations, either with
existent entities or with other non-existents.[7] According to
this view, the fact that Phar Lap won the Melbourne Cup is a fact about Phar
Lap, even though Phar Lap no longer exists. Exactly what sort of properties can
non-existents have on this view? Usually it is held that most ordinary
properties, such as having hair and being made of wood, are indeed
existence-entailing. Properties that are not thought to be existence entailing
are properties like being the subject of propositional attitude ascriptions and
the properties of having ordinary properties in the past and future [Salmon
1998: 290–1]; [Hinchliff 1996: note 17].[8]
There are a couple of ways in which this sort
of presentist might construe your blue sky experience. One way might be to
identify it with how the neuron is presently, along with various non-existent
states of affairs dealing with how the neuron was in the past, and perhaps, how
it will be in the future. However, it is more than hard to believe that a
conscious state qua aggregate of
states of affairs could exist unless all of its parts exist; an existing
aggregate must have existing parts. A better idea would be to identify the
experience with present and non present-tensed facts about the neuron itself.
One such fact might be the past-tensed fact that the neuron was a constituent of a certain now
non-existent firing of that neuron. Notice that this idea closely resembles the
account of your blue sky experience attributed to presentists who believe that
all properties are existence-entailing. The only difference is that here the
relevant non present-tensed facts are facts about the neuron and non-existent
states of affairs, rather than facts about the neuron and the property of
neuronal firing. So the problems I raised earlier for thinking of conscious
states as being made up of non present-tensed properties apply here also.
At this point, it might occur to presentists
that I have misconstrued their position, and that this misconstrual is
responsible for the difficulties just outlined. To explain this thought we need
to discuss the presentist treatment of events.
Imagine you are a servant at the court of Henry
VIII. At the end of a rather large meal he gorges on a dismembered chicken. He
raises a hand from his fulsome belly and passes it lethargically across his
mouth, signalling the end of his transaction with the plate. After rubbing his
greasy fingers indelicately through his beard he settles back. And then he lets
out the loudest, longest belch you have ever heard. Just as it is reaching its
apex, you whisper to yourself, ‘That’s some belch!’
For tenseless theorists, the belch taken as a
whole is part of the furniture of the world. This event has earlier and later
parts, ranging from the first tones that puncture the silence and the crescendo
that rapidly builds, through to the stunningly sustained apex and the gradual
release into a low, self-satisfied rumble. Each of these parts exists, and
thus, the temporally extended sum of these parts exists. In other words, the
belch exists. Presentists cannot say this, since it is never the case that more
than one configuration of Henry’s lungs, vocal cords and mouth exists.
Presentists regard talk that seems to imply the existence of events as
elliptical talk about existing things and what is happening to them [Prior,
1968]. So, when you whisper mid-belch, ‘That’s some belch!’, you are not
implying that a belch qua event
exists. You imply only that Henry is in the process of belching. But it is
never the case that there exists something that is a belch.
Taking these facts into consideration, it might
be claimed that I have simply misrepresented presentism. I began by arguing
that if an identity theory of the mind is accepted, then prima facie your blue sky experience has temporal extension. It
could be said that I went some of the way towards accommodating presentism when
I wondered whether that experience could be wholly located in the metaphysical
present, albeit at the cost of including non present-tensed states of affairs
as its constituents. But perhaps I did not go far enough. In my dim way I
continued to treat experience as if it were some kind of entity. Had I followed
things through properly, it would have become clear that if experience is
something that happens over time, then for the presentist there is no existing series of neuronal firings that
responds to blue; there is only one neuronal state existing after another. So,
just as there is the property of being in the process of belching, there is the
property of being in the process of experiencing blue. And just as there are no
belches, there are no blue sky experiences. Therefore, the arguments presented
earlier against the thought that your blue sky experience could be situated in
the durationless metaphysical present were misdirected.
In general, I have no quarrel with the
presentist’s distaste for reifying changes and processes. In terms of serving
our everyday practical interests, it usually makes no difference whether we
think of changes and processes as entities (things which exist). When we say
that a thing has changed in some way, our interest is just in contrasting the
way the thing is before the change with the way it is after the change. When we
talk of a thing’s having undergone a certain process, the nature of our interest is a little broader. We do not
care simply about the contrast between how the thing is before and after it has
undergone the process. We care also about how
it went from being in its pre-change state to its post-change state. And this
involves our being interested in the sequence of states that the thing is in
while it is undergoing the process. None of these considerations, however,
suggest that in terms of our practical involvement with changes and processes
it matters to us whether changes exist.
I may care, for instance, that the traffic light has changed from green to red,
but for all practical purposes, it does not matter whether there is an ordered
pair of light states, ágreen, redñ, which exists and can be identified
with the change.
I doubt that avoiding the reification of
changes produces deep metaphysical difficulties for presentism. However, I
claim that the processes directly involved in the production of consciousness
are special cases. Under the assumption of physicalism, the failure to reify
these processes commits us to the elimination of conscious experience.
Just as tables and chairs exist, so do qualia.[9]
If physicalism is right, then qualia are in fact sequences of neuronal firings.
And if qualia exist, then these sequences of neuronal firings must also exist.
But if presentism is right, then we cannot reify such sequences.
Do qualia really exist? Suppose you are playing cricket. You are fielding in an
attacking catching position. As such, you are very close to the batsman. In
fact, if the bowler bowls a poor delivery and the batsman aims a hefty swing in
your direction (and bat meets ball) you are almost defenceless. And this is
just what happens. The ball hits you on the thigh and sharp pain coruscates
through your leg. I claim that the pain you feel exists. I claim that you have
non-inferential warrant that it exists.[10] Moreover, it
is not obvious that there is good reason for accepting cricket bats, balls and
bruised legs in your ontology but excluding pains. Certainly, I think that the
burden of proof lies with those who wish to give bats and pains a different
ontological status.
Of course, the fact that I make these claims does not guarantee their truth. I suspect that some people will agree with me on these points, but that, perhaps, others may demur. It is hard to argue for claims of non-inferential warrant. And notoriously, there is often disagreement over such claims. In order to reach a dialectically satisfying position I need arguments. To that end, consider the following cases.
Case 1.
Alan is dawdling along the street when he is hit by a distracted
cyclist. It hurts. Alan continues to feel pain for some days.
Case 2.
Alan is hit by the distracted cyclist. From t1 to t2 he undergoes the minimal amount of neural activity required for him to
feel any pain whatsoever. Immediately after, he is obliterated by an errant
cruise missile.
Case 3.
Like Case 2, except that at some t
between t1 and t2, (before he has completed the
minimal amount of neural activity required for him to feel any pain whatsoever)
Alan is obliterated by an errant cruise missile.
Look at Case 2. The presentist needs to say
that no pain exists, but that between t1 and t2 Alan
is in the process of experiencing pain. Now transfer your attention to Case 3.
Take an arbitrarily selected t
between t1 and t2. What does the presentist say about
whether, at t, Alan is in the process
of experiencing pain?
There appear to be two options; Alan is not in
the process of experiencing pain or he is in the process of experiencing pain.
Consider the first option. If we say that at t in Case 3 Alan is not in the process of experiencing pain, then
how do we justify saying that at the corresponding time in Case 2 Alan is in
the process of experiencing pain? The only way, it seems to me, of supporting
an asymmetry between the cases is by appealing to those future-tensed facts
about Alan’s neural activity which obtain in Case 2 (but not in Case 3). And
this is dubious because it looks as though, at t in Case 2, Alan has the property of being in the process of
experiencing pain in virtue of things that will happen to him. And this is
suggestive of backwards causation. And invoking backwards causation for normal cases of conscious experience is
most undesirable.[11]
Even if this objection is wrongheaded, I still suspect it is implausible to say
that Alan is not in the process of experiencing pain at t in Case 3. I will now motivate this suspicion.
Consider the second option, according to which Alan is, at t in Case 3, in the process of experiencing pain. I think that this is the correct option to take. However, I will argue that this in fact turns out to be a consideration against the presentist metaphysics of conscious experience. Compare Case 3 with an adjunct to Case 1:
Case 4.
Jonas is changing a wheel on his bicycle which was damaged by a
collision with a dawdling pedestrian. Just as he removes the warped wheel he is
obliterated by an errant cruise missile.
Jonas did not finish changing the wheel. Does
that mean that he was not in the process of changing the wheel when the missile
arrived? It does not. It is not usually a condition of being in the process of R-ing that the process ends up being
completed. What sort of conditions are there, then? I will mention two. First,
and most obvious, is that completion of the process is possible. If I start
following a diet and exercise regime with the intention of weighing eighty and
eighty-five kilograms simultaneously, then when I give up after a couple of
months, no one is going to say that I was, before I gave up, in the process of
becoming eighty and eighty-five kilograms. Second, I suspect, is some sort of
counterfactual completion condition. I am not going to try and specify that
condition in detail here. However, in very broad outline, we would say that
Jonas was in the process of changing a wheel because Jonas was a competent
wheel changer, and if things had gone along as they usually do when competent
people try to change wheels, then Jonas would have completed the process.
Thus, I also think it is reasonable to agree
that in Case 3, Alan was in the process of experiencing pain at t; had a wildly improbable event not
intervened the process would have been completed. Tenseless theorists can use
similar reasoning and agree that at t
Alan was in the process of experiencing pain. For the tenseless theorist, there
is an existing sequence of neural states, s,
which, while not actually comprising an experience, could have been parts of an
experience. And had Alan not been obliterated at t2, s would have been part of an experience.
Tenseless theorists can therefore distinguish between
being in the process of experiencing pain and having a pain experience. And
this is important, because, if the neural picture I have presented is correct,
then a person can be in the process of producing conscious experience without
thereby succeeding in producing it; Case 2 is an example of success, whereas
Case 3 exemplifies failure.
Presentists are not in a position to draw this
distinction. The only way that presentists have of parsing phenomenal
vocabulary is in terms of being in the process of having an experience. And as
I have already indicated, this does not give us the resources we need to
classify Case 2 as one where there is phenomenal experience and Case 3 as one
where there is not.
I have argued that presentism is not compatible
with mind/body identity theories. An important part of my argument involved the
view that presentism is committed to the present’s having no temporal
extension. The motivation cited for this view was Augustine’s argument. Perhaps
it is time to re-evaluate that motivation. I doubt that it is ironclad. I will
argue that a presentist can coherently hold that the metaphysical present has
duration. However, I will also argue that ultimately, coming to this
realisation does not help to square presentism with physicalism.
It is assumed in the premises of the argument
that any stretch of time may be divided into further stretches of time. Perhaps
this assumption could be questioned. Certain ancient Greeks questioned it. They
maintained that there are atomic intervals—that is, intervals which have no
proper parts. If presentists adopt this view, they can say that the present is
indivisible even though it is extended. And this means that the presentist is
not touched by the attempted reductio,
since it depends upon the falsity of temporal atomism. But we can see that this
is not going to help the presentist. For what matters here is not merely that
the present has extension, but that it has parts. The neural correlates of
consciousness have distinct temporal phases. A durational present without parts
does not have the mereological structure required to support the neural
correlates of consciousness. Temporal atomism is not helpful.
However, I doubt that we need to resort to
temporal atomism in order to find a version of durational presentism that is
coherent. The view that the metaphysical present has duration and has parts is coherently describable.
Once this view has been properly described, it turns out that Augustine’s
objection rests on an equivocation. Before this point can be established,
however, it is necessary to flesh out the notion of durational presentism.
Consider an interval which has as parts every
interval that exists. This interval indicates the boundaries of the present.
Let’s introduce a special technical expression to denote this sort of interval:
let’s call it a big interval. As time
passes, there is change with respect to which set of intervals exists, and
therefore big intervals pass in and out of existence. To distinguish the
picture we are developing from the atomistic view previously considered, we
will stipulate that big intervals are not atomic—they have proper parts.
Note that I am assuming a reductionist view of
the nature of instants and intervals. I mention this because what I have said
above may sound confusing if the reader has in mind a substantival view. Here,
instants and intervals are being construed as constructions from their
‘contents’. Thus, any change in terms of what exists, marks the destruction of
one big interval and the generation of another. This way of putting things is
purely a matter of convenience. A substantival view of instants, according to
which instants and intervals are entities distinct from their contents, could
just as easily have been assumed. On a substantival view, there would be no
reason to talk of big intervals going in and out of existence. We would merely
speak of their contents as changing.
Now, suppose that we are interested in the
details of how big intervals pass in and out of existence. We might start by
dividing the ways in which big intervals pass in and out of existence into two
broad versions. Each way, I will argue, can be defended from Augustine’s
objection.
According to the first version, when a big
interval goes out of existence it leaves nothing behind. More precisely, no
part of a big interval will be a part of the next big interval.[12]
According to the second version, a big interval does leave something behind. It
goes out of existence by losing a proper
part, thereby making way for a new big interval. Putting this second view
more pictorially, think of the present as a worm that gains segments at one end
while losing them at the other. A segment is ‘born’ at one end of the worm and
passes along the length of the worm to the other end, where it is annihilated.
To each such generation and annihilation corresponds a distinct big interval.
Now, recall the two principles that were
crucial in the reconstruction of Augustine’s argument against a durational
present:
(1) If x and y are present then they are simultaneous.
(2)
If x and y do not temporally overlap then they are not simultaneous.
I think that a defender of durational
presentism ought to say that (1) and (2) equivocate over ‘simultaneous’.
According to durational presentism, time has
two importantly different aspects. First, there is the concrete temporal
extension embodied by the big interval. The big interval is made up of
sub-intervals and instants, such that these sub-intervals and instants (and
their contents) stand in relations of precedence and simultaneity to each
other. Second, there are tensed facts about how the contents of the big
interval were, how they are, and how they will be.
The durational presentist ought to connect the
sense of ‘simultaneous’ in (1) with the second aspect. Thus, the correct
understanding of ‘simultaneous’ in (1) is as follows:
x is simultaneous1 with y iff x and y are present.
On the other hand, the sense of ‘simultaneous’ relevant to (2) ties in with the first aspect:
x is simultaneous2 with y iff x and y are located at
the same concrete moments of the big interval.
Once we distinguish these two senses of
‘simultaneous’ we can agree x and y’s being present and non-overlapping
entails that they are simultaneous1 and non- simultaneous2. But
since it is consistent for x and y to be simultaneous1 and not
simultaneous2, no contradiction can be derived in
Augustine’s way from durational presentism.
Given that durational presentism survives
Augustine’s argument, how does it fare with respect to squaring presentism with
physicalism? First, consider the version which says that when a big interval
goes out of existence, it leaves nothing behind. An apparent drawback to this
view involves the question of what makes one end of the big interval the
earlier end, and the other the later end. Since each big interval comes into
existence complete, as it were, it seems that an account has to be given which
is separate from the story about the passing of big intervals in and out of
existence. This is likely to be unattractive to many presentists qua tensed theorists, who prefer to
account for any talk of earlier/later in terms of tensed notions.
There is another drawback to this view, which
pertains to consciousness. Suppose that Kate is such that whenever she has an
experience it is always neatly enclosed by the metaphysical present. Let l stand for the length of the
metaphysical present. Now suppose that Kate’s entire life were shifted
backwards by l/2. In an intuitive
sense, Kate would have had the same neural history, but she might have no
conscious experiences whatsoever, because the contents of the metaphysical
present never have the right properties.
Notice that these reservations need not apply
to the other version of durational presentism. This version says that big
intervals go out of existence by losing proper parts. The question of why one
end of the big interval is the earlier end and the other is the later end can
be answered without having to appeal to anything outside the passing of big
intervals in and out of existence. We can simply say that x is earlier than y iff x and y exist and x did exist
while y did not exist.[13]
One unusual consequence of this view is that any interval smaller than the big
interval has a history, in the sense that it has past and/or future-tensed
properties. For example, consider two non-overlapping intervals, d and e. Suppose that d is
earlier than e. It then turns out
that it was the case that it was not the case that d is earlier than e. This
is because at one stage, d existed
while e did not. It might be thought
that the notion of intervals themselves as things that have histories is
absurd, and that this consequence alone is enough to thoroughly discredit this
version of presentism. However, the notion of intervals having past or future
tensed properties does not strike me as absurd, but merely a little unkempt.
Notice also that so long as the longest
temporal part of the big interval having no past tensed properties is brief
enough, the problem of Kate’s history being shifted back by half the length of
the big interval does not arise. This is because what exists is replaced very
gradually.
Still, this second version of durational
presentism faces a serious objection if it is invoked as a way of allowing
presentists to be physicalists. In fact, the objection applies equally well to
both versions of durational presentism.
The objection takes the form of a dilemma.
Suppose that the actual world, Wa,
is a presentist world with a metaphysical present long enough to enclose the
conscious experience you are now having. Further suppose that the present is
also brief enough to ensure that it does not enclose successive conscious
experiences of yours. Now imagine another world, Wb, which is just as the actual world is except that the
duration of the metaphysical present is four times longer than it actually is.
In Wb, the metaphysical
present is long enough to enclose successive experiences of yours. Does the
presentist say that Wb is
a world where there are conscious experiences? This is the dilemma.
If the answer is yes, then any reasons we might
have for endorsing presentism begin to fade. After all, if the present can be
durational, there is no reason at all to suppose that the metaphysical present
is not long enough to encompass entire lifetimes, centuries, millennia, etc.
Moreover, once we admit that the metaphysical present could be long enough for
both a and b to coexist, it becomes hard to see what sort of reasons we might
have for supposing that in the actual world the metaphysical present is not
arbitrarily long. This sort of presentism has no apparent advantages over the
tenseless view of time.
If the answer is no, then a concern is that
consciousness turns out to be extrinsic in an unpalatably bizarre way. Let a be a conscious state of yours. And
suppose that it will pass out of the metaphysical present to be replaced by an
incompatible conscious experience, b.
In Wb, however, both a and b are enclosed by the same metaphysical present. So a’s being a conscious state in Wa is constituted in part by
there being nothing located at a portion of the metaphysical present earlier or
later than a that otherwise has all
the right features to be a conscious state. Such a restriction has little
plausibility beyond a pathological desire to defend durational presentism. We
might ask, for instance, how a double success could be a failure? Admittedly,
this remark has no currency as an argument against the restriction (since thus
construed, it clearly begs the question), but it does convey something of the
incredulity with which the restriction deserves to be met.
I will mention here the only independent
motivation for the restriction that I can imagine. And it is an embarrassingly
poor one. a and b, as previously noted, are incompatible experiences. The usual way
of understanding this incompatibility is by noting that a and b cannot be
instantiated relative to the same person and same time. Thus, it is perfectly
acceptable for one person to instantiate a
and another to instantiate b at the
same time. Likewise, it is perfectly acceptable for one person to instantiate a and b at different times. The restriction we are considering suggests
that if a and b are both located in the big interval, then they must be
instantiated relative to different persons. In other words, it is acceptable
for a and b to both be experiences of the one person so long as those
experiences never coexist. If this is the rationale, then it’s pretty clear
that it must apply to any pair of incompatible properties whatsoever. And that
effectively means that no qualitative change at all could occur within the big
interval. This means that the only feasible version of durational presentism
would be one where the times of the big interval were substantival, so that it
is not big intervals that come in and out of existence, but only their
contents. This leads to disaster.
First, the second version of durational
presentism has it that the contents of the big interval change gradually by the
accretion of new contents at one end and the loss of the oldest ones at the
other. However, if it is not possible for there to be qualitative variation
within a big interval, then on this view, anything that persists throughout the
big interval could never change. Since, ex
hypothesi, nothing can have incompatible properties at different times
within the big interval, and since the contents of the big interval change only
gradually, any qualitative change in a thing would usher in a big interval
featuring such incompatible properties. In short, this makes qualitative change
impossible. We can be pretty sure that the actual world is not like this!
Moreover, both versions of durational
presentism are supposed to allow for the existence of the neural correlates of
consciousness. But if neither can allow for qualitative change within the big
interval then neither can do justice to the neural correlates of consciousness,
which are jam-packed with qualitative change.
So either path offered by the dilemma I have
presented leads the durational presentist to an unsatisfactory conclusion. I
conclude that durational presentism does not, after all, help to square
presentism with physicalism.
11. Craig and the Non-Metrical Present
Having argued that physicalism and presentism
are at odds, I want to look briefly at a suggestion, which if correct, would
mean that my arguments founder on a fundamental misunderstanding of presentism.
Presentist William Lane Craig urges that ‘There
is no such thing as “the present” simpliciter:
it is always “the present _____,” where the blank is usually filled by a
reference to some thing or event. The
duration of the present will be as long or as short as the event or thing under
discussion.’ [Craig 2000: 245.]
Craig follows Prior in identifying presentness
with existence.[14] He then observes that, since it is a mode of
being, ‘presentness does not involve metrical ideas.’ [246.] And this means that ‘there is no privileged
unit in which temporal becoming occurs.’ [ibid.] Thus, according to Craig, the question I have been focusing on,
namely, the extent of the present simpliciter,
is ill-founded. Presumably, he would
also say that any conclusions I have drawn from ruminating over this question
are also ill-founded.
I think Craig is right, qua presentist, to identify presentness with existence. However, I don’t agree that this means the
question I have been focusing on is ill-founded. I do concur that, strictly speaking, the question “How long is
existence?” is a nonsensical one. But
the question of the extent of the present can be sensibly phrased in terms
which do not presuppose that “How long is existence?” makes sense. Here is a
question for the presentist that does seem to be coherent: “What things exist,
and what are the relationships that hold between them?” Of course, this is a rather broad
question. However, a full answer to
this question will tell us whether there exist any entities which are
non-simultaneous2.
If the presentist does not like the question
“How long is the metaphysical present?” because it reeks of incoherence, we can
rephrase the question in terms of whether there are temporal separation
relations between existing things. This
question is coherent and ought to
admit of an answer. If the
presentist answer is yes, then in my terms, the metaphysical present has
duration. Should the presentist answer
‘no’, then in my terms, the metaphysical present lacks duration.
For presentists who want to say that the metaphysical
present is durationless, a more satisfactory treatment of issues surrounding
the neural correlates of consciousness can be given if they embrace dualism.
For dualists, conscious states are either states of non-physical entities
(substance dualism) or states of physical entities, where the physical entity
instantiates non-physical mental properties (property dualism).[15]
The dualist presentist can admit that the
neural correlates of your blue sky experience include a bevy of non
present-tensed states of affairs, and yet deny that the experience itself has
any non present-tensed constituents. This is because the neural correlates of
consciousness are not identified with conscious states, but are merely
correlated with them. If there is a mind/body dualism then the presentist has a
means of escape from the difficulties I have presented.
The situation with respect to durational
presentism is interesting. I suspect that important parts of the objection I
gave against mind/body identities in the context of durational presentism could
be adapted to apply also to the case of dualism. However, in terms of my
current objectives it is sufficient if I have shown that presentists ought to
be dualists.
Facts about the temporal properties of
conscious experience are difficult to reconcile with presentism. I have argued
that the only plausible way to reconcile consciousness with presentism is to
endorse a mind/body dualism. To the extent that dualism is problematic so too
is presentism. Of course, some presentists
are dualists. In particular,
presentists like Craig, who are also Christians, may not be so concerned about
the conclusions drawn here.
Notice, however, that even if on balance we
ought to be dualists, my arguments nevertheless undermine presentism to some
degree. To the extent that we are unsure about dualism we ought also to be
unsure about presentism. However, since the the tenseless theory of time is
compatible with both dualism and physicalism, uncertainty about whether we
ought to be dualists does not translate into uncertainty about whether we ought
to be tenseless theorists.[16]
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[1]See, for instance, [Prior 1970: 246–7] and [Craig 1997].
[2]Note, however, that in some quarters it is thought that some correlates of consciousness are to be found in sub-cortical regions like the thalamus. See, for instance, [Baars and Newman 1994].
[3]On the modularity of the cerebral cortex, see also [Thompson 1993: Ch. 8].
[4]See [Place 1956] and [Smart 1959].
[5]See [Braddon-Mitchell & Jackson 1996: 98–100] for an argument that functionalists should retain restricted type identities.
[6]See [Bigelow 1996] for more details.
[7] [Routley 1980: Ch. 2]; [Salmon 1998]; [Hinchliff 1996].
[8]It is probably safe to say that most presentists think that all properties (and relations) are existence-entailing. See [Prior 1967: Ch. 8], [Christensen 1976: 137], [Lloyd 1978], [Williams 1981: 109–110], [Bigelow 1996: 36–9], and [Craig 1997].
[9]Here, I do not mean the controversial reading which takes qualia to be ineffable phenomenal items. Qualia in this sense seem incompatible with physicalism. Instead, I mean the minimal understanding according to which qualia are phenomenal ‘feels’.
[10]This does not commit me to an extreme Cartesian position according to which, necessarily, if you believe that you are in pain then you are in pain.
[11]You might wonder if this problem is exclusive to presentism. Suppose we modify Case 2 so that the metaphysical backdrop is one of tenseless time rather than presentism. Isn’t there still a sense in which, at t, Alan is in the process of experiencing pain? And doesn’t this fact depend on what is happening neurally to Alan later than t? If backwards causation needs to be invoked for the presentist version of this scenario, doesn’t it need to be invoked here as well? The answer to the first two questions is yes, but the answer to the third is no. The difference between the cases is that, for the tenseless theorist, being in the process of experiencing pain is a derivative property based on purely mereological considerations. Assuming as we are at the moment, that Alan can be truly said to be in the process of experiencing pain at t in Case 2 but not in Case 3, we can give the following tenseless account of being in the process of experiencing pain at t: Alan is in the process of experiencing pain at t iff Alan has a pain experience which is partially located at t.
[12]Though this is true for the most part, there could be (very unusual) degenerate cases. Here is an example. Suppose a particular big interval encompasses a time which comprises world-state W. Further suppose that the world leaves state W but soon returns to that state, so that the following big interval includes a time which also comprises state W.
[13]To completely avoid the worry about providing a tensed account of temporal order, it must be the case that the bits of reality that come into, and go out of, existence are not themselves intervals with proper (temporal) parts. That is, they must either be instantaneous or embody atomic intervals.
[14] Or, more accurately, with temporal
existence. Craig wants to allow for the
possibility of timeless existence [Craig 2000: 246].
[15]For a contemporary defence of substance dualism, see [Eccles and Popper 1977]. For defences of property dualism, see [Jackson 1982] and [Chalmers 1996].
[16] I am grateful to
John Bigelow, James Chase, Mark Colyvan, Ian Gold, Toby Handfield, John Heil,
Cathy Legg, John O’Dea and two AJP
referees for helpful comments and discussions.
I would also like to thank the Philosophy Program at the Research School
of Social Sciences, Australian National University, where some preliminary work
for this paper was undertaken. I would
also like to acknowledge the financial assistance of the Monash University
Postgraduate Publications Award.