Scientific realists take the contrary view that the success of a theory does give us reason to believe in the theoretical entities it posits. Among other arguments, they sometimes appeal to the idea that entities that at one time were unobservable later became observable with the rise of new technologies, such as telescopes, electron microscopes, and ordinary microscopes. This shows, they argue, that the boundary between observable and unobservable entities is not sharp enough to justify skepticism about the latter.
In chapter 4
of his book Scientific Representation, van Fraassen
presents a very clever and interesting challenge to this sort of argument. Taking on scientific realists on what might
seem to be their strongest ground, he denies that even ordinary microscopes must
be seen as confirming the reality of previously unobserved entities.
First a
terminological point. Consider the world
of everyday experience – of tables and chairs, rocks and trees, reflections in
water and shadows on the ground and on walls, rainbows and clouds and stars in
the sky, and so on. These are all
examples of “phenomena” as van Fraassen uses the term. In holding that the aim of science is
empirical adequacy, views like his are often characterized as holding that
science is concerned only to “save the phenomena.” Scientific realism, by contrast, holds that
science gives us reason to believe in an invisible world behind the phenomena.
The claim on
the table, then, is that a microscope amounts to “a window on the invisible world,”
as van Fraassen puts it (p. 93). It
allows us to peer behind the phenomena to what previously had been
unobservable. Van Fraassen allows that
this is one possible interpretation. But
he argues that it is not the only one, so that instruments like microscopes
cannot be appealed to as somehow settling the dispute between constructive empiricism
and scientific realism. Considered by
themselves they are neutral, insofar as what they yield can be interpreted in
ways consistent with either position.
Scientific
instruments, notes van Fraassen, play several roles. Sometimes that role is representative, as in the case of clocks, balances, and measuring
rods. Sometimes it is imitative in the sense of mimicking
effects that occur in nature, as when an electrical generator is used to bring
about an imitation of lightning. Sometimes
the role is instead productive, in
the sense of bringing about phenomena which had not previously been observed,
as when Faraday discovered electromagnetic induction.
Now, a
microscope is a scientific instrument. What
role does it play? The scientific
realist, in conceiving of it as a kind of “window” on otherwise unobservable
reality, thinks of it as playing an essentially representative role. But whether or not it plays that role, van
Fraassen says, it certainly plays the productive
role of creating new phenomena, phenomena that had not been seen before. And he wants to argue that there is nothing
in what they show us that compels us to see them as doing anything more than
that.
Here he
appeals to the idea of a “public hallucination” (p. 101). Hallucinations like the one Macbeth
experienced when he thought he saw a dagger are private, directly knowable only
to the individual experiencing them.
Contrast that with a rainbow, which, like Macbeth’s dagger, is not
something really out there in the world, but is nevertheless experienced by
many individuals at once.
But not all
public hallucinations are quite as distant from really existing things as
that. Van Fraassen draws a distinction
between four types of “images” we distinguish from reality, but which are not
all equally distant from it. At one
extreme we have private images such
as after-images, dreams, and hallucinations, which are not only not actual
things in the objective world, but are accessible only to the individual person
having the experience. At the other
extreme we have graven images such as
paintings, photographs, and sculptures.
These are not really things of the
same sort as what they resemble, but they nevertheless are things in their
own right really existing in the world outside the mind.
In between
are public hallucinations, but these can be divided into two sub-classes. There are public hallucinations that are, as
van Fraassen puts it, “not ‘copy’-qualified” (p. 104). What he means is that they are not images of some thing that is really out there
in the world. Rainbows and mirages would
be examples. They are a step up from private
images because they are shared rather than subjective. But there are also public hallucinations that
are “copy-qualified,” in the sense
that they are images “of” something
really there in the world. Examples
would be shadows and reflections, such as the reflection of a tree in the
water. These are a step down from graven
images, because a reflection is, like a rainbow, not an actual thing out there
in the world. But it is of a thing (for example, the tree) in a
way a rainbow is not. Hence it is a step
up from a public hallucination of the kind that is not copy-qualified.
It is in
this last category that van Fraassen wants to put the images seen in a
microscope. What a microscope gives is,
he argues, is a public hallucination of the copy-qualified kind, like a tree’s
shadow or reflection in the water. By no
means does he want to deny that we do, of course, get much useful information
from microscopes and other scientific instruments. But this, he argues, is due to “our latching
onto significant regularities in the
phenomena” rather having to do with unobserved realities (p. 109).
As always
with van Fraassen, there are further intriguing nuances, examples, and insights,
and I can’t convey them all here in this summary. But I think I have captured the gist of his
argument. It seems to me that the scientific
realist can make the following points in response.
First, while
there are similarities between the case of a tree’s reflection in water and the
case of an image seen in a microscope, there are also important
differences. As I was reading van
Fraassen’s book, I sipped a martini.
Through the glass I could see the books on the shelf behind it – only very
obscurely through the part of the glass that still had liquid in it, a little
bit more clearly through the part that did not.
But though the books were obscured, it seems correct to say that I was
looking at the books themselves –
even though I was doing so through
the medium of the glass – rather than that I was looking at an image in the
glass. I was also wearing eyeglasses,
and when I peered past the martini glass to the books it seems even more
obviously correct to say that what I was looking at were the books, even if I looked at them through the eyeglasses (rather than saying that I was looking at an
image in the eyeglasses).
These cases
are obviously different from the case of looking at a reflection of a tree in
the water. In that case, what I am
looking at is not the tree itself, but something caused by the tree. As van Fraassen emphasizes, the reflection of
the tree is not a thing there in the
water in the sense in which a floating log is a thing there in the water. The reflection will, for example, seem to move
as you keep looking at it while you move along the shore, whereas a floating
log might not do so. That’s why it is
plausible to classify the reflection as a kind of “public hallucination.” By contrast, the books I see through the
martini glass and through the eyeglasses are
things there in the world. And even
given that the martini glass distorts the appearance of the books, the result
is not a hallucination of any kind, precisely because I really am nevertheless
looking at the books.
Now, the
case of the microscope seems obviously closer to the cases of the martini glass
and the eyeglasses than it does to the case of the reflection of the tree. What you see when using a microscope to
examine a cell, for example, is the cell
itself – even if you’re looking at it through
the microscope – rather than merely an image.
If that is the case, though, then it also seems plausible after all to conceive
of a microscopes as a “window on the invisible world,” rather than merely as
something that creates new phenomena.
A second
point in reply to van Fraassen would be this.
Suppose the argument I just gave is wrong, and that van Fraassen is
right to characterize what a microscope produces as a “copy-qualified public
hallucination.” It is not clear that that
would actually support constructive empiricism over scientific realism. After all, what makes an image “copy-qualified”
is that there is a real thing that the image is an image of. For example, a tree’s
reflection in the water is copy-qualified because there really is a tree that
is causing it. The fact that the
reflection is a “public hallucination” therefore would hardly support
anti-realism about trees!
But then, if
an image in a microscope is also a “copy-qualified” image, then that would mean
that there must a real thing that the image is an image of. And that would arguably be sufficient grist
for the scientific realist mill, even if we don’t think of microscopes as
windows on the invisible world.
Related
posts:
Cartwright
on theory and experiment in science
Cartwright
on reductionism in science
Dupré
on the ideologizing of science
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