Where the Conflict Really Lies: Science, Religion, and Naturalism (41 page)

Given materialism, therefore, beliefs are (ordinarily) long-standing neural events. As such, they have NP properties, but also content properties: each belief will have the property of having such and such a proposition as its content. NP properties are
physical
properties; on the other hand content properties—for example the property of having as content the proposition
all men are mortal
—are
mental
properties. Now how, according to materialism, are mental and physical properties related? In particular, how are content properties related to NP properties—how is the content property of a particular belief related to the NP properties of that belief?

Materialists offer fundamentally two theories about the relation between physical and mental properties (and hence two theories about the relation between NP properties and content properties): reductive materialism and nonreductive materialism. According to Sir Francis Crick: “your joys and your sorrows, your memories and your ambitions, your sense of personal identity and free will, are in fact no more than the
behaviour of a vast assembly of nerve cells and their associated molecules.”
¹⁸
This is a pretty good statement of
reductive
materialism, according to which (naturally enough) mental content properties are
reducible to
NP properties; according to
nonreductive
materialism, content properties are not reducible to NP properties, but are
determined by
(supervene on) NP properties.
¹⁹
We could put it like this: according to reductive materialism, there is only one kind of property in the neighborhood: NP properties, some of which are also mental properties. According to nonreductive materialism, on the other hand, there are
two
kinds of properties, NP properties and also mental properties, which are not NP properties, but are determined by NP properties.

Suppose we think first about reductive materialism. Consider the property of having as content the proposition
naturalism is vastly overrated
, and call this property “C.” On reductive materialism, C
just is
a certain combination of NP properties. It might be a disjunction of such properties: where P
₁
to P
_n
are NP properties, C, the property of having the content in question, might be something like (where “v” represents “or”)

P
₁
v P
₂
v P
₃
v P
₈
v…. P
_n

More likely, it would be something more complicated: perhaps a disjunction of conjunctions, something like (where “&” represents “and”)

(P
₁
&P
₇
&P
₂₈
&…) v (P
₃
&P
₃₄
&P
₁₇
&…) v (P
₈
&P
₈₃
&P
₁₀₇
&…) v…
²⁰

If complex combinations of NP properties are themselves NP properties, content properties, on reductive materialism, are really just a special kind of NP property. According to reductive materialism, therefore content properties—for example, the property of having
naturalism is vastly overrated
as content—are or are reducible to NP properties.

That’s one of the two proposals made by materialists. The other is that a content property isn’t an NP property, and can’t be reduced to NP properties, but is nevertheless
determined by
NP properties. Here the basic idea is this: for any particular mental property M you pick, there is a physical property P such that necessarily, if a thing has M, then it has P, and if a thing has P, then it has M.
²¹
So take any mental property—for example, the property of being in pain: there will be some physical property P (presumably an NP property), such that it’s true in every possible world that whatever has P is in pain, and, conversely, whatever is in pain has P.
²²
Specified to content and NP properties, the idea is that for any content property C that a neural structure can have, there is an NP property P such that if a neural structure has that content property C, it has P, and conversely, any neural structure that has P also has that content property C.

According to both reductive and nonreductive materialism, mental properties are determined by physical properties (and indeed according to reductive materialism mental properties just
are
physical properties). As we go up the evolutionary scale, we find neural structures with greater and greater complexity. Near one end of the scale, for example, we find bacteria; presumably they have no beliefs at all. At the other end of the scale there are human beings, who have a rich and varied store of beliefs
and whose brains contain many billions of neurons connected in complex and multifarious ways, so that the number of different possible brain states is more than astronomical. And the idea is that as you rise in the evolutionary scale, as you go through more and more complex neural structures, at a certain point there arises something we can properly call a belief, something that is true or false. At a certain level of complexity, these neural structures start to display belief content. Perhaps this starts gradually and early on—perhaps it is with
C. elegans
, a small but charismatic beast that enjoys the distinction of having its nervous system completely mapped. Possibly
C. elegans
displays just the merest glimmer of consciousness and just the merest glimmer of actual belief content, or perhaps belief content shows up further up the scale; that doesn’t matter. What does matter is that at a certain level of complexity, neural structures begin to display content and the creatures that harbor those structures have beliefs. This is true whether content properties are reducible to NP properties or supervene on them.

So (given materialism) some neural structures, at a certain level of complexity of NP properties, acquire content; at that level of complexity, NP properties determine belief content, and the structures in question are beliefs. And the question I want to ask is this: what is the likelihood,
given evolution and naturalism
(construed as including materialism about human beings), that the content thus arising is in fact
true
? In particular, what is the likelihood, given N&E, that the content associated with
our
neural structures is true? What is the likelihood, given N&E, that our cognitive faculties are reliable, thereby producing mostly true beliefs?

We are now ready to state the reasons for the first premise of the main argument, which, as you recall is

(1) P(R/N&E) is low.

Of course we all commonsensically assume that our cognitive faculties are for the most part reliable, at least over a large area of their functioning. I remember where I was last night, that I’ve just had oatmeal for breakfast, that my elder son’s name is not Archibald, that a year ago I didn’t live in the house I live in now, and much else besides. I can see that the light is on in my study, that the flower garden is overgrown with weeds, and that my neighbor put on weight over the winter. I know a few truths of mathematics and logic, mostly pretty simple, no doubt, but still… The natural thing to assume, and what we all do assume (at least before we are corrupted by philosophy or neuroscience) is that when our cognitive faculties aren’t subject to malfunction, then, for the most part, and over a wide area of everyday life, the beliefs they produce in us are true. We assume that our cognitive faculties are reliable. But what I want to argue is that the naturalist has a powerful reason
against
this initial assumption, and should give it up. I don’t mean to argue that this natural assumption is false; like everyone else, I believe that our cognitive faculties
are
, in fact, mostly reliable. What I do mean to argue is that the
naturalist
—at any rate a naturalist who accepts evolution—is rationally obliged to give up this assumption.

As you recall, we are thinking of naturalism as including materialism, which, as we’ve seen, comes in two varieties: reductive and nonreductive. Let’s think first about the question from the point of view of nonreductive materialism. Return to the evolutionary scale and
C. elegans
, that celebrated little worm, and suppose that it is in
C. elegans
that we first get belief. No doubt such belief will be primative
in excelsis
(and if you don’t think
C. elegans
has beliefs, you can simply go up the scale until you encounter creatures you think do have beliefs), but let’s suppose members of this species have beliefs. Now given that
C. elegans
has survived for millions of years, we may assume that its behavior is adaptive. This behavior is produced or caused by the neurological structures in the
C. elegans
nervous system; we may further assume, therefore, that this neurology is adaptive. This underlying neurology causes adaptive behavior; as Churchland says, it gets the body parts where they must be in order to survive. But (in line with nonreductive materialism) it also determines belief content. As a result, these creatures have beliefs, which of course have a certain content.

And here’s the question: what reason is there for supposing that this belief content is
true
? There isn’t any. The neurology causes adaptive behavior and also causes or determines belief content: but there is no reason to suppose that the belief content thus determined is true. All that’s required for survival and fitness is that the neurology cause adaptive behavior; this neurology also determines belief content, but whether or not that content is
true
makes no difference to fitness. Certain NP properties are selected for, because they contribute to fitness. These NP properties also cause or determine belief content; they associate a content or proposition with each belief. The NP properties are selected, however, not because they cause the content they do, but because they cause adaptive behavior. If the content, the proposition determined by the neurology (the NP properties of the belief) is true, fine. But if it is false, that’s no problem as far as fitness goes.

Objection: consider a frog on a lily pad. A fly buzzes by; the frog’s tongue flicks out and captures the fly. If this frog is to behave successfully, adaptively, there must be mechanisms in it that register the distance to the fly at each moment, its size, speed, direction, and so on. Aren’t these mechanisms part of the frog’s cognitive
faculties? And don’t they have to be accurate in order for the frog to behave adaptively? And isn’t it therefore the case that the frog’s cognitive mechanisms must be accurate, reliable, if the frog is to survive and reproduce? Or consider an animal, maybe a zebra, grazing on the veldt; a lion approaches. The zebra notices the predator; this noticing consists in part of some neural structure arising in its brain, perhaps a certain pattern of firing of neurons in the optical portion of its brain, and perhaps this pattern ordinarily arises in response to the appearance of a predator in the middle distance. If this structure isn’t properly correlated with the presence of predators, the zebra won’t be long for this world. And wouldn’t this structure, furthermore, be part of the creature’s cognitive mechanisms? And don’t those mechanisms have to be accurate, reliable, if the zebra is to survive?

Reply: that frog clearly does have “indicators,” neural structures that receive input from the frog’s sense organs, are correlated with the path of the insect as it flies past, and are connected with the frog’s muscles in such a way that it flicks out its tongue and captures that unfortunate fly. The same goes for the zebra: if it is to behave adaptively (evade predators, for example) it too will have to have indicators, neural structures that monitor the environment, that are correlated (for example) with the presence of predators, and are connected with its muscles in such a way as to cause it to flee when a predator threatens.

Now if we like, we can include these indicators under the rubric “cognitive faculties.” The important point to see here, however, is that indication of this sort does not require
belief
. In particular, it does not require belief having to do with the state of affairs indicated; indeed it is entirely compatible with belief
inconsistent
with that state of affairs. For example, anaerobic marine bacteria (so the story goes) contain magnetosomes, tiny internal magnets that indicate magnetic north; in the oceans of the northern hemisphere, this direction is down,
towards the oxygen-free depths.
²³
These indicators are connected with the propulsion devices of the bacteria in such a way as to cause these creatures, which can’t flourish in the oxygen-rich surface water, to move towards the deeper water. But this in no way requires that the bacteria form
beliefs
. Fleeing predators, finding food and mates—these things require cognitive devices that in some way track crucial features of the environment, and are appropriately connected with muscles; but they do not require true belief, or even belief at all. The long-term survival of organisms of a certain species certainly makes it likely that its members enjoy cognitive devices that are successful in tracking those features of the environment—indicators, as I’ve been calling them. Indicators, however, need not be or involve beliefs. In the human body there are indicators for blood pressure, temperature, saline content, insulin level, and much else; in these cases neither the blood, nor its owner, nor anything else in the neighborhood ordinarily holds beliefs on the topic. The objector is therefore right in pointing out that fitness requires accurate indication; but nothing follows about reliability of belief.