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which can only be `evoked'. The distinction is, for Bacon, both obvious and unimportant. There is
some evidence that it really matters only after 1800, when the very conception of `seeing' undergoes
something of a transformation. After 1800, to see is to see the opaque surface of things, and all
knowledge must be derived from this avenue. This is the starting point for both positivism and
phenomenology. Only the former concerns us here. To positivism we owe the need to distinguish
sharply between inference and seeing with the naked eye (or other unaided senses).
Positivist observation
The positivist, we recall, is against causes, against explanations, against theoretical entities and
against metaphysics. The real is restricted to the observable. With a firm grip on observable reality the
positivist can do what he wants with the rest.
What he wants for the rest varies from case to case. The logical positivists liked the idea of using
logic to `reduce' theoretical statements, so that theory becomes a logical short-hand for expressing
facts and organizing thoughts about what can be observed. On one version this would lead to a
wishy-washy scientific realism: theories may be true, and the entities that they mention may exist, so
long as none of that talk is understood too literally.
In another version of logical reduction, the terms referring to theoretical entities would be shown, on
an analysis, not to have the logical structure of referring terms at all. Since they are not referential,
they don't refer to anything, and theoretical entities are not real. This use of reduction leads to a fairly
stringent anti-realism. But since nobody has made a logical reduction of any interesting natural
science, such questions are vacuous.
The positivist then takes another tack. He may say with Comte or van Fraassen that theoretical
statements are to be understood literally, but not to be believed. As the latter puts it, in The Scientific
Image, `When a scientist advances a new theory, the realist sees him as asserting the (truth of the)
postulate. But the anti-realist sees him
((170))
as displaying this theory, holding it up to view, as it were, and claiming certain virtues for it' (p. 27). A
theory may be accepted because it accounts for phenomena and helps in prediction. It may be
accepted for its pragmatic virtues without being believed to be literally true.
Positivists such as Comte, Mach, Carnap or van Fraassen insist in these various ways that there is
a distinction between theory and observation. That is how they make the world safe from the ravages
of metaphysics.
Denying the distinction
Once the distinction between observation and theory was made so important, it was certain to be
denied. There are two grounds of denial. One is conservative, and realist in its tendencies. The other is
radical, more romantic, and often leans towards idealism. There was an outburst of both kinds of
response around 196o.
Grover Maxwell exemplifies the realist response. In a 1962 paper he says that the contrast between
being observable and merely theoretical is vague. It often depends more on technology than on
anything in the constitution of the world.' Nor, he continues, is the distinction of much importance to
natural science. We cannot use it to argue that no theoretical entities really exist.
In particular Maxwell says that there is a continuum that starts with seeing through a vacuum.
Next comes seeing through the atmosphere, then seeing through a light microscope. At present this
continuum may end with seeing using a scanning electron micro-scope. Objects like genes which were
once merely theoretical are transformed into observable entities. We now see large molecules. Hence
observability does not provide a good way to sort the objects of science into real and unreal.
Maxwell's case is not closed. We should attend more closely to the very technologies that he takes
for granted. I attempt this in the next chapter, on microscopes. I agree with Maxwell's playing down of
visibility as a basis for ontology. In a paper I discuss later in this chapter, Dudley Shapere makes the
further point that physicists regularly talk about observing and even seeing using devices in which
neither the eye nor any other sense organ could play any
((footnote:))
1 G. Maxwell, `The ontological status of theoretical entities', Minnesota Studies in the Philosophy of Science 3 (1962), pp. 3-27.
((171))
essential role at all. In his example, we try to observe the interior of the sun using neutrinos emitted
by solar fusion processes. What counts as an observation, he says, itself depends upon current theory.
I shall return to this theme, but first we should look at the more daring and idealist-leaning rejection
of the distinction between theory and observation. Maxwell said that the observability of entities has
nothing to do with their ontological status. Other philosophers, at the same time, were saying that
there are no purely observation statements because they are all infected by theory. I call this idealist-
leaning because it makes the very content of the feeblest scientific utterances determined by how we
think, rather than mind-independent reality. We can diagram these differences in the following way:
Conservative response (realistic): there is no significant
distinction
Positivism: (a sharp between observable and
distinction between unobservable entities.
theory and observation)
Radical response
(idealistic): all
observation statements
are theory-loaded.
Theory-loaded
In N.R. Hanson gave us the catchword `theory-loaded' in his splendid book, Patterns of Discovery.
1959
The idea is that every observational term and sentence is supposed to carry a load of theory with it.
One fact about language tends to dominate those parts of Patterns of Discovery in which the word
`theory-loaded' occurs. We are reminded that there are very subtle linguistic rules about even the most
commonplace words, for example the verb `to wound' and the noun `wound'. Only some cuts, injuries,
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