Stanford University

Constructive Empiricism (Stanford Encyclopedia of Philosophy)

1.1 Contrast with Scientific Realism

Constructive empiricism is a view which stands in contrast to the type
of scientific realism that claims the following:

Science aims to give us, in its theories, a literally true story of
what the world is like; and acceptance of a scientific theory involves
the belief that it is true. (van Fraassen 1980, 8)

In contrast, the constructive empiricist holds that science aims at
truth about observable aspects of the world, but that science does not
aim at truth about unobservable aspects. Acceptance of a theory,
according to constructive empiricism, correspondingly differs from
acceptance of a theory on the scientific realist view: the
constructive empiricist holds that as far as belief is concerned,
acceptance of a scientific theory involves only the belief that the
theory is empirically adequate.

1.2 On Literalness

Even given her stance about what theory acceptance involves, a
constructive empiricist can still understand scientific theories
literally.   What makes for a literal understanding of a
theory?  While van Fraassen does not offer a full-fledged account
of literalness in The Scientific Image, he does offer the
following two necessary conditions for a theory’s being understood
literally:

  1. The theory’s claims are genuine statements capable of truth or
    falsity.
  2. Any literal construal of a theory cannot change the logical
    relationships among the entities claimed by the theory —
    “most specifically, if a theory says that something exists, then
    a literal construal may elaborate on what that something is, but will
    not remove the implication of existence” (1980, 11).

In insisting on an understanding of scientific theories as literally
true, the constructive empiricist sides with the scientific realist
against conventionalists, logical positivists, and instrumentalists.
While advocates of these latter positions may take scientific theories
to be true, they do so only by interpreting those theories in
non-standard ways — in ways that, for instance, violate (1) or
(2) above.

1.3 Contrast with Logical Positivism

One of the reasons constructive empiricism is viewed as significant is
that it carries on the tradition of the logical positivists without
being saddled with the problematic aspects of the positivists’
positions. The constructive empiricist follows the logical positivists
in rejecting metaphysical commitments in science, but she parts with
them regarding their endorsement of the verificationist criterion of
meaning, as well as their endorsement of the suggestion that
theory-laden discourse can and should be removed from science. Before
van Fraassen’s The Scientific Image, some philosophers had
viewed scientific anti-realism as dead, because logical positivism was
dead. Van Fraassen showed that there were other ways to be an
empiricist with respect to science, without following in the footsteps
of the logical positivists.

1.4 A Doctrine about Aims

Constructive empiricism has the look of an epistemological view about
what one should believe — namely, that one should be agnostic
about the claims about unobservables that our scientific theories
make. But the view is not intended to be read in that way.
Constructive empiricism is to be understood as a doctrine about what
the aim of science is, not a doctrine about what an individual should
or shouldn’t believe.

To make this clear, we can, following van Fraassen (1998, 213), make
the following terminological distinction:

scientific agnostic: someone who believes the science s/he
accepts to be empirically adequate but does not believe it to be true,
nor believes it to be false.

scientific gnostic: someone who believes the science s/he
accepts to be true.

It’s clear, in light of this distinction, that one can be a scientific
gnostic and a constructive empiricist — one would simply choose
to have beliefs that go beyond what science is aiming at. There is, of
course, a connection between the scientific realist/constructive
empiricist dichotomy and the scientific gnostic/scientific agnostic
dichotomy:

Scientific realists think that the scientific gnostic truly
understands the character of the scientific enterprise, and that the
scientific agnostic does not. The constructive empiricist thinks that
the scientific gnostic may or may not understand the scientific
enterprise, but that s/he adopts beliefs going beyond what science
itself involves or requires for its pursuit. (van Fraassen 1998,
213–214)

A final point to make about aims is that the constructive empiricist
distinguishes between the aim of an individual scientist or group of
scientists (which may be fame, glory, or what have you) and the aim of
science itself. The aim of science determines what counts as success
in the enterprise of science as such (van Fraassen 1980,
8).   Because constructive empiricists do not identify the
aim of science with whatever goals the majority of scientists may
have, they deny that constructive empiricism is a thesis in sociology
subject to the kind of empirical confirmation or disconfirmation any
scientific thesis faces.  Instead, constructive empiricism is to
be understood as a philosophical description of science that seeks to
explain how an empiricist can regard the activity of science as
consistent with the empiricist’s own standards of rational activity.
Like the interpretation of any human activity, constructive empiricism
is constrained by the “text” of the scientific activity it
interprets. Within those constraints, it succeeds or fails according
to its ability to provide an interpretation of science that
contributes to our understanding of science, making intelligible to us
various elements of its practice. (van Fraassen 1994,
188–192)

1.5 Empirical Adequacy

Here is a rough-and-ready characterization of what it is for a theory
to be empirically adequate:

a theory is empirically adequate exactly if what it says about the
observable things and events in the world is true — exactly if
it ‘saves the phenomena.’ (van Fraassen 1980, 12)

A sufficiently unreflective constructive empiricist might adopt this
construal of empirical adequacy for her theory, but a more
sophisticated constructive empiricist would probably embrace an
account of empirical adequacy akin to that which van Fraassen develops
later in The Scientific Image

To understand that account, one needs first to appreciate the
difference between the syntactic view of scientific theories
and van Fraassen’s preferred semantic view of scientific
theories. On the syntactic view, a theory is given by an enumeration
of theorems, expressed in some one particular language. In contrast,
on the semantic view, a theory is given by the specification of a
class of structures (describable in various languages) that are the
theory’s models (the determinate structures of which the theory holds
true). As van Fraassen says,

To present a theory is to specify a family of structures, its models;
and secondly, to specify certain parts of those models (the empirical
substructures) as candidates for the direct representation of
observable phenomena. (1980, 64)

A theory is empirically adequate, then, if appearances —
“the structures which can be described in experimental and
measurement reports” (1980, 64) — are isomorphic to the
empirical substructures of some model of the theory. Roughly speaking,
the theory is empirically adequate if the observable phenomena can
“find a home” within the structures described by the
theory — that is to say, the observable phenomena can be
“embedded” in the theory. See Figure 1 for a graphical
illustration of the relations that make a theory empirically adequate
on van Fraassen’s view, with the cloud shapes representing the relata
of the isomorphism relation.

empirical adequacy diagram
Figure 1: A Theory’s Empirical Adequacy

This conception of a theory’s empirical adequacy is arguably what
allows a constructive empiricist to avoid the kind of doxastic
commitment Friedman (1982, 278) and Rochefort-Maranda (2011, 61-62)
describe as posing a problem for the constructive empiricist (a
problem that Rochefort-Maranda subsequently attempts to solve). Here
is that problem:

Since we might initially think that sentences about observables are,
according to a theory, equivalent to certain sentences about
unobservable entities, we might also think that commitment to belief
in the existence of the observables undesirably commits the
constructive empiricist to the existence of the corresponding
unobservable entities. (And so correspondingly, agnosticism about the
unobservables undesirably commits the constructive empiricist to
agnosticism about the equivalent observables.)

The constructive empiricist arguably dissolves this problem by
invoking the above conception of empirical adequacy.
(Rochefort-Maranda gestures in the direction of, but does not
explicitly describe, this dissolution in his footnote 1.) Belief that
a theory is empirically adequate amounts to the belief that the
observables can be properly embedded in at least one of the theory’s
models. Belief in the possibility of that embedding does not require
the constructive empiricist to take the truth of sentences about
observables to entail the truth of sentences about unobservables. By
taking a theory to be empirically adequate, the constructive
empiricist is simply saying that the phenomena we observe (and believe
to exist) can exist within the structure the theory describes, without
additionally being committed to saying that the unobservable parts of
that theoretical structure are parts of the actual structure of the
world.

Note that the phenomena relevant to a theory’s empirical adequacy are
all actual observable phenomena (1980, 12). So for a theory
to be empirically adequate, it has to be able to account for more than
just the phenomena that have actually been observed and the phenomena
that will be observed. See Section 3.4 below for a discussion of the
worry that the constructive empiricist’s belief in the empirical
adequacy of her accepted theories thereby extends beyond what a bona
fide empiricist ought to believe.

1.6 What’s Observable

Insofar as the empirical adequacy of a theory amounts to the
embeddability of observable phenomena within substructures of the
theory’s models, the constructive empiricist’s account of empirical
adequacy rests heavily on the distinction between what is observable
and what is not. If, as it is natural to think,‘is
observable’ is a vague predicate, we should not expect there to
be a precise demarcation between what’s observable and what’s
unobservable. Observability can still serve as a useful concept in the
philosophy of science, as long as there are clear cases of
observability and clear cases of unobservability.

Here is one rough characterization of observability:

X is observable if there are circumstances which are such
that, if X is present to us under those circumstances, then
we observe it (van Fraassen 1980, 16).

For the constructive empiricist, this characterization is “not
meant as a definition, but only as a rough guide to the avoidance of
fallacies” (van Fraassen 1980, 16). It is important to clarify
that, as a constructive empiricist would use the terminology, one only
observes something when the observation is unaided. One does
not see cells through a microscope; instead one sees an image, an
image which the scientific gnostic understands one way but the
scientific agnostic understands a different way.

Note that the observability of interest is relativized to
“us,” the members of the epistemic community whose
scientific theories are the topic of interest. Since what counts as
observable is relative to what epistemic community the observer is
part of, and since the members of that epistemic community are the
subject of scientific theory, the constructive empiricist takes what
counts as observable as the subject of scientific theory and not
something that can be determined a priori (van Fraassen 1980,
56–59). Science itself, then, is ultimately the arbiter of what
counts as observable. For worries about circularity in the use of
accepted scientific theory to determine which parts of the world are
observable (and hence to determine which theories of science are
empirically adequate and thereby candidates for acceptance), see
Section 3.7 below.

1.7 Acceptance

Acceptance has both an epistemic and a pragmatic component. When one
accepts a theory, one has a belief, and also a commitment. The belief
is that the theory is empirically adequate. The commitment is “a
commitment to the further confrontation of new phenomena within the
framework of that theory, a commitment to a research programme, and a
wager that all relevant phenomena can be accounted for without giving
up that theory” (1980, 88). According to the constructive
empiricist, this commitment is made at least in part on pragmatic
grounds: there is an important role for non-epistemic values in theory
choice (van Fraassen 2007, 340).

For the constructive empiricist, acceptance comes in degrees. This can
influence how one engages in discourse in the domain of the
theory:

If the acceptance is at all strong, it is exhibited in the person’s
assumption of the role of explainer, in his willingness to answer
questions ex cathedra. (van Fraassen 1980, 12)

Van Fraassen goes on to explain that acceptance produces contexts
where one engages in discourse “in a context in which language
use is guided by that theory.”

One reason the constructive empiricist’s account of acceptance is
important is that it allows us to make sense of scientific
anti-realists such as constructive empiricists (of the scientific
agnostic variety) talking as if a particular theory is true. When one
looks at scientific discourse, this is what scientists are often
doing: they treat a theory as if they fully believe it, and answer
questions and give explanations using the resources of the theory. The
constructive empiricist can account for this behavior, without
attributing full belief in the theory to the scientists, by describing
the scientists as merely accepting, without fully believing, the
theories they develop (van Fraassen 1980, 81–82).

The constructive empiricist can acknowledge that scientific realists
also recognize that there is a pragmatic dimension to theory
acceptance. But “because the amount of belief involved in
acceptance is typically less according to anti-realists, they will
tend to make more of the pragmatic aspects” (van Fraassen 1980,
13).

2.1 Poor arguments for constructive empiricism

Before turning to stronger arguments for constructive empiricism, it
will be helpful to draw attention to a couple scientific anti-realist
arguments that the constructive empiricist would be well-advised not
to use in support of her view.

First, consider the Argument from Underdetermination. This argument
starts by pointing out that for any theory, there are rival theories
that are empirically equivalent to it — the theories make all
the same predictions about what’s observable, but differ only with
regard to what’s unobservable. The argument goes on to say that it
follows that all the empirically equivalent theories are equally
believable, and hence belief in the truth of any one of those
empirically equivalent theories must be irrational.

While the constructive empiricist view is a view about the aims of
science and not a normative theory in epistemology, the constructive
empiricist is an individual who values the sort of epistemic modesty
which might motivate one to harbor anti-realist sympathies in general.
To the extent that the constructive empiricist embraces epistemic
modesty, she might also be an epistemic voluntarist, a person who
believes that “rationality is only bridled irrationality”
(van Fraassen 1989, 172). Any behavior that does not make one
inconsistent or incoherent is rational, by the voluntarist’s lights.
Such an attitude might seem the natural epistemic one for the
constructive empiricist to hold, insofar as the constructive
empiricist is impressed by the cognitive limits that prevent us from
having conclusive evidence in favor of any one particular theory.

One reason the constructive empiricist would be well-advised not to
embrace the Argument from Underdetermination, then, is that it goes
against a voluntarist position in epistemology. (This point is clearly
made by Van Dyck 2007, 19–22, and agreed to by van Fraassen
2007, 347.) By the voluntarist’s reckoning, going beyond the evidence
to the extent that one chooses to believe in the truth of a theory,
both in its observable and unobservable aspects, could very well be
rational.

The relatively permissive epistemological view of a constructive
empiricist who is also an epistemic voluntarist helps explain why such
a constructive empiricist would be prudent not to take constructive
empiricism to be a normative theory concerning the deliverances of
science. Mistakenly understood in that normative way, constructive
empiricism would imply that belief in a theory’s empirical adequacy is
the only rational candidate for the belief involved in a theory’s
acceptance. Such a constraint on the rationality of opinion is clearly
at odds with any epistemic voluntarism the constructive empiricist
might embrace.

Gideon Rosen (1994, 160–161) gives another reason that the
constructive empiricist ought not accept underdetermination arguments
as grounds for constructive empiricism. Consider the following two
hypotheses:

  1. T is empirically adequate — i.e., T is
    adequate to all observable phenomena, past, present, and future.
  2. T is adequate to all phenomena observed so far.

As Rosen notes, one’s current evidence does not tell in favor of
either hypothesis over the other. So by an underdetermination-style
argument, one is not justified in believing either hypothesis. But
belief in (A) is the belief the constructive empiricist contends is
involved in theory acceptance. (For more on how one might take Rosen’s
argument as an argument against constructive empiricism, see Section
3.4 below.)

The second scientific anti-realist argument a person would be
well-advised not to use in support of constructive empiricism is the
Pessimistic Induction Argument. This argument points out that
scientific theories in the past have been shown to be false, so by
induction, we should think that current theories are false, too. If
this argument is taken to have the conclusion that belief in our
current theories is irrational, then, as above, the argument is
incompatible with any voluntarism the constructive empiricist might
embrace. The argument is also incompatible with the view of a
constructive empiricist who, in the skeptical spirit of anti-realist
views in general, rejects reasoning based on a principle of induction.
Van Fraassen, for instance, writes: “I do not think that there
is such a thing as Induction, in any form” (2007, 343).

2.2 Empirical Adequacy versus Truth

So how might one argue for constructive empiricism? One argument for
constructive empiricism hinges on the fact that belief in the
empirical adequacy of a theory is less epistemically audacious than
belief in the truth of the theory. Both beliefs, of course, go beyond
the evidence:

In either case we stick our necks out: empirical adequacy goes far
beyond what we can know at any given time. (All the results of
measurement are not in; they will never all be in; and in any case, we
won’t measure everything that can be measured.) (van Fraassen 1980,
69)

So why is belief that a theory is empirically adequate preferable to
the belief that the theory is true? Van Fraassen famously and pithily
puts the point as follows:

it is not an epistemological principle that one might as well hang for
a sheep as for a lamb. (1980, 73)

The constructive empiricist rejects arguments that suggest that one is
rationally obligated to believe in the truth of a theory, given that
one believes in the empirical adequacy of the theory.

For this epistemological argument to work, the distinction between
empirical adequacy and truth has to be well-founded. A significant
part of The Scientific Image is devoted to that task. As
described in Section 1.6, the constructive empiricist argues that one
can make sense of the observable/unobservable distinction, even if
observation is theory-laden. (If the distinction between observables
and unobservables didn’t make sense, the concept of empirical adequacy
would be incoherent.)

Rosen (1994, 161–163), as well as Monton and van Fraassen (2003,
407–408), offers an additional rationale for the constructive
empiricist’s embrace of empirical adequacy rather than truth as the
hallmark of the belief component of theory acceptance. One might
reasonably think of belief in the empirical adequacy of accepted
theories as the weakest attitude one can attribute to scientists at
the same time that one is still able to make sense of their scientific
activity. At the same time, belief in the empirical adequacy of a
theory is sufficiently cautious as to allow the believer to remain
faithful to the spirit of empiricism. Thus, constructive empiricism is
a view which allows one to regard the activity of science as activity
the empiricist can safely endorse.

2.3 The Relationship Between Theory and Experiment

The constructive empiricist argues that constructive empiricism
“makes better sense of science, and of scientific activity, than
realism does” (van Fraassen 1980, 73). The constructive
empiricist can be understood as giving two arguments for this claim;
the first argument will be presented here, and the second argument
will be presented in the next subsection.

Constructive empiricists might maintain that, for working scientists,
the real importance of scientific theories is that they are a factor
in experimental design. They contrast this with the traditional
picture presented by philosophy of science. According to the
traditional picture, the main goal of scientific practice is to
discern the fundamental structure of the world, and experimentation
simply is used to determine whether theories should be taken to be
true, and hence as contributing to our knowledge of the fundamental
structure. The constructive empiricist, in contrast, suggests that the
reason a scientist turns to a theory is that experimental design is
difficult, and theories are needed to guide experimental inquiry. But
what scientists are really aiming to discover, according to the
constructive empiricist, are “facts about the world —
about the regularities in the observable part of the world” (van
Fraassen 1980, 73).

Van Fraassen argues for this position in part by describing Millikan’s
famous experiment measuring the charge of the electron. Scientific
realists take this experiment to be making a discovery about the
nature of the unobservable entities known as electrons. Van Fraassen,
in contrast, presents the experiment as “filling in a value for
a quantity which, in the construction of the theory, was so far left
open” (1980, 77). In doing the experiment, Millikan was
discovering a regularity in the observable part of the world, and was
providing a value for a quantity in atomic theory. Millikan need not
be understood as discovering something about the nature of
unobservable objects in the world. Van Fraassen says that in a case
like Millikan’s,

experimentation is the continuation of theory construction by
other means
. The appropriateness of the means follows from the
fact that the aim is empirical adequacy. (1980, 77)

2.4 The Pragmatics of Theory Choice

Another way in which, according to the constructive empiricist,
constructive empiricism makes better sense of science than realism
does has to do with theory choice. Some virtues that scientists see in
theories are pragmatic virtues, not epistemic virtues. This shows that
scientists are choosing between theories using criteria other than
truth.

What virtues are pragmatic? Here is what van Fraassen says:

When a theory is advocated, it is praised for many features other than
empirical adequacy and strength: it is said to be mathematically
elegant, simple, of great scope, complete in certain respects:
also of wonderful use in unifying our account of hitherto
disparate phenomena, and most of all, explanatory. (1980, 87)

Some scientific realists might hold that some of these are epistemic
virtues, not pragmatic virtues. With regard to simplicity, the
constructive empiricist can recognize that scientific realists
sometimes hold that simpler theories are more likely to be true, but
at the same time the constructive empiricist can contend that

it is surely absurd to think that the world is more likely to be
simple than complicated (unless one has certain metaphysical or
theological views not usually accepted as legitimate factors in
scientific inference). (1980, 90)

With regard to explanation, constructive empiricists recognize that
scientific realists typically attach an objective validity to requests
for explanation (van Fraassen 1980, 13), but constructive empiricists
do not grant that objective validity. Van Fraassen’s arguments that
explanation is pragmatic constitute a significant part of The
Scientific Image
, and will be discussed in the next
subsection.

Constructive empiricists recognize that these pragmatic factors like
simplicity and explanatory power are important guides in the pursuit
of the aim of science (van Fraassen 1980, 89). But they insist that
these factors are valuable in that pursuit only insofar as their
consideration advances the development of theories that are
empirically adequate and empirically strong. The factors do not have
special value as indicators of the truth of what the theories say
about the unobservable parts of the world.

2.5 The Pragmatics of Explanation

Scientific realists, by contrast, sometimes say that they believe in
the truth of scientific theories because the theories provide a
satisfying explanation of the observable phenomena, an explanation
that unifies what would otherwise be disparate observations. The
constructive empiricist is not moved by such considerations:

A person may believe that a certain theory is true and explain that he
does so, for instance, because it is the best explanation he has of
the facts or because it gives him the most satisfying world picture.
This does not make him irrational, but I take it to be part of
empiricism to disdain such reasons. (van Fraassen 1985, 252)

Indeed, one can recognize the explanatory power of a theory without
taking it to be true. Van Fraassen points out that theories can
explain well even if they are false. Newton’s theory of gravitation
explains the motion of the planets and the tides, “Huygens’s
theory explained the diffraction of light, Rutherford’s theory of the
atom explained the scattering of alpha particles, Bohr’s theory
explained the hydrogen spectrum, Lorentz’s theory explained clock
retardation.” But none of these theories is now thought to be
true.

For the constructive empiricist, the explanatory power of a theory
amounts to nothing more than the theory’s ability to provide certain
bits of information in response to contextually defined queries. 
Scientific explanation amounts to the highlighting of various aspects
of the structure postulated by the theory, to answer, in a
contextually dependent way, various questions of interest to us (van
Fraassen 1980, 124).  Science, then, contributes nothing to
explanation over and above the descriptive and informative content of
the scientific theory: “a success of explanation is a success of
adequate and informative description” (van Fraassen 1980,
156–157). Explanation cannot be reduced to that content, though,
since explanation cannot occur unless an appropriate question, offered
in a particular context, is provided.  Explanation thus goes
beyond what science reveals to us. The constructive empiricist can
hence avoid saddling scientists with a commitment to the unobservable
entities invoked in such explanations, properly claiming that such
commitments are not licensed by the activity of science.  (See
Kitcher & Salmon 1987 for the view that even if requests for
explanation are contextually delimited, what counts as a good /
relevant explanation depends also on non-contextual factors.)

A fair portion of the constructive empiricist’s account of scientific
explanation is thus devoted to an explication of the contextual
dependence of explanation. Among other reasons given in favor of that
contextual dependence, van Fraassen points out that explanations are
typically causal in character — they attempt to situate the
event-to-be-explained in the “causal net” postulated by
the scientific theory. Which events in that net are picked out as
“the” cause(s) of some event-to-be-explained depend upon
the interests of the individuals asking the explanatory question
(1980, 124–126).

Explanation will frequently involve the invocation of counterfactuals,
often of the form: if event B had not occurred, neither would event A
have (van Fraassen 1980, 118). That’s because (as just noted)
explanations are frequently causal in character, and analyses of
causation typically invoke some sort of counterfactual. Another
component of the constructive empiricist’s efforts at showing
explanation to be context-dependent, then, amounts to his exposition
of the context dependence of counterfactuals.

Van Fraassen points out that any counterfactual has a ceteris paribus
clause, but what is “being kept equal” by the asserter of
the counterfactual varies from context to context. For example,
consider the counterfactual, “If Tom were to light the fuse,
there would be an explosion.” If the ceteris paribus clause of
the speaker keeps constant the fact that the fuse leads to a barrel of
gunpowder, and the fact that lit fuses leading to barrels of gunpowder
typically result in explosions, then the counterfactual would, in that
context, be true. If, on the other hand, the ceteris paribus clause of
the speaker also kept constant the fact that Tom is generally paranoid
about explosions around barrels of gunpowder and fuses, and would only
light the fuse if he had disconnected the fuse from the barrel, then
the counterfactual would, in that context, be false (1980, 116). 
Until the context that fixes the ceteris paribus clause is specified,
we cannot say what the truth value of the counterfactual in question
is. Only once the context is determined does the counterfactual admit
of an objective truth value.

One of the reasons the constructive empiricist highlights the context
dependence of explanation is that she wishes to show how efforts at
explaining various parts of the world extend beyond the activity of
science. Since, for instance, the propositions of science are not
context-dependent in character, but the counterfactuals involved in
explanation are, we have reason to think that explanation involves
something more than the descriptive information science gives us:
namely, the context-dependent interests of the individual seeking an
explanation in answer to some question. Also, if (as seems likely) the
concept of a law of nature has to be understood in a counterfactual
way, counterfactuals’ context-dependence implies that those laws, too,
go beyond what science reveals to us (van Fraassen 1980, 118).

It should be clear here, then, that the constructive empiricist’s
efforts at showing explanatory efforts to extend beyond the activity
of science are part of an effort to show that the scientific realist
is mistaken in thinking that science gives us reason to think that
claims about causation, laws of nature, and other counterfactuals
represent objective, context-independent truths about the world.

Scientific realists might point out that constructive empiricists do
allow that explanatory power can count as a pragmatic virtue of a
theory (van Fraassen 1980, 89). But, one might naturally think, no
scientist can acknowledge the explanatory power of a theory without
taking the theory to be true. So, continues the scientific realist,
the constructive empiricist cannot admit the usefulness of explanatory
power to the scientist without also regarding the scientist as taking
her theories to be true.

The constructive empiricist disagrees. Among other reasons, she can
cite the earlier mentioned explanatory power of false theories. 
Additionally, the constructive empiricist might insist that use of a
theory need not entail a commitment to the theory’s entire ontology. A
person offering an explanation speaks from within the language of the
theory she accepts. Consistent with that acceptance, she is
“conceptually immersed” within the theory. But such use of
language need not reflect the individual’s epistemic commitment, which
may be merely to take the theory to be empirically adequate (van
Fraassen 1980, 151–152). So, for instance, talk of possibility
and necessity can be thought of not as talk about some objective
modality in nature, but as talk of what phenomena fit in the models of
the accepted theory (van Fraassen 1980, 201–202).
X is possible’ can be interpreted as
X appears in some model of the theory,’ while
X is necessary’ can be read as ‘X
appears in every model of the theory.’ Again, the constructive
empiricist sees the scientist as “immersing” herself in
the world of the theory, talking as if the theory were true, with
language reflecting the structure of the theory. But she need not take
the theory’s modal structure to correspond to any in reality.

2.6 Avoiding Inflationary Metaphysics

We can see in the above discussion of the pragmatics of explanation
why the constructive empiricist thinks constructive empiricism can
help us to make sense of science “without inflationary
metaphysics” (van Fraassen 1980, 73). By “inflationary
metaphysics,” van Fraassen has in mind the scientific realists’
typical beliefs in, for example, laws of nature, natural kinds, and
objective modality.

The constructive empiricist recognizes that believing in empirical
adequacy involves sticking our necks out, just as believing in truth
does; nonetheless,

… there is a difference: the assertion of empirical adequacy is
a great deal weaker than the assertion of truth, and the restraint to
acceptance delivers us from metaphysics. (van Fraassen 1980, 69)

Scientific realists might not be moved by this consideration, because
they might not see any problem with inflationary metaphysics. The
point of The Scientific Image, according to van Fraassen, was
to answer the question: what should an empiricist think about science?
Since an empiricist would want to avoid inflationary metaphysics, this
consideration would move them to favor constructive empiricism. The
question of why one would want to be an empiricist is taken up in van
Fraassen’s 2002 book, The Empirical Stance.

3.1 The Miracle Argument

One way that the constructive empiricist might indirectly support
constructive empiricism is by taking issue with Hilary Putnam’s
miracle argument for scientific realism. This argument holds that
scientific realism “is the only philosophy that doesn’t make the
success of science a miracle” (Putnam 1975, 73). Putnam goes on
to argue that the statements that a scientific realist would make
about our mature scientific theories are “part of the only
scientific explanation of the success of science.” To give an
adequate scientific description of science, scientific realism needs
to be assumed.

Putnam’s basic idea is as follows: if the scientific theories are
false, why would they be so successful? Van Fraassen famously replies
with an evolutionary analogy:

I claim that the success of current scientific theories is no miracle.
It is not even surprising to the scientific (Darwinist) mind. For any
scientific theory is born into a life of fierce competition, a jungle
red in tooth and claw. Only the successful theories survive —
the ones which in fact latched on to actual regularities in
nature. (van Fraassen 1980, 40)

Van Fraassen’s point is that a theory can be empirically adequate, and
hence latch on to the observable regularities in nature, without being
true. The scientific competition between theories hinges on which
theory accurately describes the observable world; it does not hinge on
which theory is actually true. Thus, it would not be miraculous for
science to arrive at an empirically adequate, scientifically
successful, yet false theory. (See the discussion of the Miracle
Argument in the entry on
scientific realism
for more on the miracle argument as a consideration in favor of
scientific realism.)

3.2 Inference to the Best Explanation

Inference to the Best Explanation is the controversial rule of
inference which basically holds that, out of the class of potential
explanations we have of some phenomena, we should infer that the best
explanation is the true one. If Inference to the Best Explanation is a
rule we do (or ought) to follow, then it looks as if scientific
realism is an accurate description (or prescription) of the aims of
science — we should acknowledge the reality of the entities our
best explanatory theories postulate, even if those entities are
unobservable.

The constructive empiricist might offer several responses to this
challenge:

  • Inference to the Best Explanation doesn’t automatically win as a
    description of scientists’ actual inferential practice, since that
    practice may be equally well described by saying that scientists
    believe our best explanatory theories to be empirically adequate
    (rather than true) (van Fraassen 1980, 20–21). Note, though,
    that the constructive empiricist does not actually endorse the rule
    that we should believe that the best explanation is empirically
    adequate (contrary to how van Fraassen, for instance, has sometimes
    been read; see, e.g., Bandyopadhyay 1997).
  • The scientific realist thinks that theories can only adequately
    explain regularities in nature if we take the theories to be true. But
    theories can explain if we merely take the theories to be empirically
    adequate. So even if we allow Inference to the Best Explanation as a
    legitimate rule of inference, the realist has to offer some additional
    reason to think “T is true” is a better explanation than
    “T is empirically adequate” (van Fraassen 1980, 21).
  • It may be that all the potential explanations we have are bad, and
    hence we would be unwise to believe that one of those explanations is
    the true one (van Fraassen 1989, 143–145). It’s plausible to
    think any argument is mistaken that suggests that we are privileged to
    hit on the right range of potential explanations to begin with.
  • Any probabilistic formulation of Inference to the Best Explanation
    is probabilistically incoherent. A Bayesian will coherently update in
    light of new evidence, but then the proponent of Inference to the Best
    Explanation wants the Bayesian to unwarrantedly give extra
    probabilistic weight to the hypothesis that is the best explanation
    (van Fraassen 1989, 160–70).

In sum, because the constructive empiricist rejects Inference to the
Best Explanation, she is not moved by arguments for scientific realism
that make use of that rule of inference. (See the discussion of
skepticism about inference to the best explanation in the entry on
scientific realism
for an elaboration of doubts about the use of inference to the best
explanation as a motivating consideration in favor of scientific
realism.)

3.3 The Observable/Unobservable Distinction

A standard type of objection to constructive empiricism, one that was
especially prevalent soon after The Scientific Image was
published, is the type of objection that takes issue with the clarity
or cogency of the observable/unobservable distinction. A few examples
of this type of objection will be presented in this section, along
with constructive empiricist replies.

By the constructive empiricist’s lights, distant macroscopic objects
are observable, since if we were nearby we could see them. Paul
Churchland (1985, 39–40) takes issue with the importance the
constructive empiricist attaches to size, as opposed to spatiotemporal
proximity. Churchland points out that it is just a contingent fact
that humans have control over their spatiotemporal location, but not
over their size. Churchland concludes that the distinction between
things that are unobserved but observable, and things that are
unobservable, “is only very feebly principled and is wholly
inadequate to bear the great weight that van Fraassen puts on
it” (Churchland 1985, 40).

Van Fraassen replies with the recognition that “scientific
realists tend to feel baffled by the idea that our opinion about the
limits of perception should play a role in arriving at our epistemic
attitudes toward science” (1985, 258). Constructive empiricists
are not asserting any metaphysical difference in the world on the
basis of the observable/unobservable distinction; they are just saying
that that distinction is relevant to the epistemic attitudes we take.
Since “experience is the sole legitimate source of information
about the world” (van Fraassen 1985, 258), it makes sense that
what we can experience influences our epistemic attitudes. (Note that
in his 2002 book The Empirical Stance, van Fraassen calls
into question his 1985 statement about experience.)

A different argument by Churchland (1985, 44–45) asks what the
constructive empiricist would say about beings who are like us except
that they are born with electron microscopes permanently attached to
their left eyes. Churchland says that the electron-microscope-eye
humanoids would count viruses as part of their ontology, and yet by
the constructive empiricist’s lights we can’t, even though we are
functionally the same as the humanoids when we put our left eye
against the viewfinder of an electron microscope.

The constructive empiricist might reply that we are not warranted in
saying that the humanoids have the experience of viruses
unless we already treat the humanoids as being part of our epistemic
community (van Fraassen 1985, 256–257). If we do expand our
epistemic community to include them, then the constructive empiricist
is happy to say that in that situation viruses are observable. But if
we do not accept them as part of our epistemic community, then we will
simply analyze them as like us, except having electron microscopes
attached to themselves, and we will say that they are “reliable
indicators of whatever the usual combination of human with electron
microscope reliably indicates” (van Fraassen 1985, 257). In that
case the extension of ‘observable’ is unchanged.

Another argument calling into question the significance of the
observable/unobservable distinction is presented by Ian Hacking (1985,
146–147). Hacking considers a machine which makes grids of the
same shape but various sizes. We can see grids with the same overall
shape of smaller and smaller size, but the machine makes some grids
that are too small to be seen with the unaided eye. When looked at
through a microscope, however, the unobservable grids are seen to have
the same shape as the observable ones. Hacking writes:

I know that what I see through the microscope is veridical because we
made the grid to be just that way. I know that the process of
manufacture is reliable, because we can check the results with the
microscope. Moreover we can check the results with any kind of
microscope, using any of a dozen unrelated physical processes to
produce an image. Can we entertain the possibility that, all the same,
this is some gigantic coincidence? (Hacking 1985, 146–147)

Hacking concludes that it would be unreasonable to be an anti-realist
about the unobservable grid, and hence we should at least sometimes
believe what science tells us about unobservables.

Van Fraassen (1985, 298) replies by pointing out an unwarranted
supposition in Hacking’s argument: the claim that we made the grid to
be that way implies what is under dispute, that the grid was
successfully made to be that way. Regarding the argument that, if
different types of microscopes make similar observations, then the
observations must be veridical, van Fraassen replies that that
argument

reveals only the unstated premise that the persistent similarities in
the relevant phenomena require, must have, a true
explanation. (van Fraassen 1985, 298)

But this is a premise that the constructive empiricist rejects.

Here van Fraassen is allowing for the possibility that the
constructive empiricist can reasonably be agnostic about the grid. Van
Fraassen replies in a similar fashion to an objection that Paul Teller
puts forth about the immediacy of objects viewed through a
microscope.

Teller (2007) claims that the images produced by many scientific
instruments require some interpretative effort for us to make
assertions about what it is that we are seeing. What we see through
optical microscopes, on the other hand, is importantly different. In
such an observation, we take ourselves to see the object being
magnified itself, immediately and without interpretative effort.

The conclusion Teller draws is that contrary to what van Fraassen
claims, what is observable extends beyond what members of our
epistemic community can observe unaided by measuring instruments. What
is observable minimally also includes the objects viewed through
optical microscopes, as well as other objects whose observation is
similarly unmediated by interpretation (132-134).

In reply, van Fraassen (2001) suggests that what we see through a
microscope is akin to reflections seen in mirrors and other reflective
surfaces — the reflection of a tree in a body of water, for
instance. In both the case of the observation via the microscope and
the object viewed in a reflection, we might assert that what we are
seeing is a real object. But van Fraassen points out an important
difference between the reflected object and our observation through
the microscope. We are confident that the reflection is of a real
object because we can observe certain invariances between the object
purportedly being observed (the tree), the reflective image, and our
vantage point. We can, for instance, see that the tree maintains a
certain fixed position relative to the reflective body, and we can see
that the angle subtended by the lines between us and the two bodies is
a particular function of the observer’s position. The observation of
these invariances is possible, in part, because the tree is itself
observable without the aid of instruments (van Fraassen 2001,
160).

That, however, is not true of the objects — the paramecia, say
— that are purportedly being observed through the microscope.
Because the paramecia are not directly observable without instruments,
we can only hypothesize that there are objects being observed for
which the invariant geometric relations hold. It is possible for us,
then, to maintain an agnosticism about the paramecia that we can’t
about the tree (160). We can regard our observations via the
microscope the same way we regard our observations of rainbows —
namely, as observations of phenomena that are public (even capable of
being captured by photographic equipment) without at the same time
being observations of some existent object (162). (We say that the
rainbow is not an actual physical object because it does not
participate in the invariant geometric relations we expect of actual
physical objects: “If the rainbow were a thing, the various
observations and photos would all locate it in the same place in
space, at any given time” (157) ).

Alspector-Kelly (2004) claims that there is not the difference
described here between aided and unaided perception. If the
constructive empiricist insists that rainbows, reflections, and the
like constitute publicly observable phenomena despite not amounting to
actually existing objects, then what we experience in the case of
unaided veridical perception is also some kind of image-like
observable phenomena:

…when we look directly at the tree we are also postulating an
appropriate relation between object, image, and vantage point, namely,
between the tree itself, our perceptual experience of the tree, and
the vantage point of our bodily location. (Alspector-Kelly 2004, 336)

Insofar as it is appropriate to speak of a perceptual image when
characterizing the view through the microscope – even when, so far as
the science of microscopy informs us, that view is veridical – it is
appropriate to speak of a perceptual image when characterizing
naked-eye visualization, even when that view is veridical.
(Alspector-Kelly 2004, 338)

If this is true, then unaided veridical perception is not
distinguished from aided perception in the way van Fraassen suggests.
Unaided veridical perception is as much mediated by image-like
observable phenomena as aided perception is.

As we will see in §3.6, the constructive empiricist might naturally
express skepticism, in the case of unaided veridical perception, about
the existence of anything like image-like phenomena. Kusch (2015)
points out one reason for skepticism: the phenomena in question
exhibit fewer of the invariant relations – “unlike, say, rainbows,
visual experience cannot be photographed” (177)- that would allow us
to characterize the phenomena as public, verifiable ones capable of
empirical study.

A constructive empiricist might also respond to Alspector-Kelly by
advocating something like a disjunctivist view of perception, denying
that what is observed in the disparate cases really is the same. On
such a view, unaided veridical perception really is of actual physical
objects, whereas perception with instrumentation results only in the
experience of some kind of publicly observable phenomena akin to
rainbows and reflections. It remains to be seen whether independent
motivation for such a view can help recommend it over the alternative
offered by the defender of microscopic observables.

3.4 Observable versus Observed

According to the constructive empiricist, “there is no purely
epistemic warrant for going beyond our evidence” (van Fraassen
2007, 343). But then why does the constructive empiricist hold that
the aim of science involves going beyond our evidence? Empiricism
wants to be epistemically modest, but belief that a theory is
empirically adequate goes well beyond the deliverances of experience.
Hence, one can object to constructive empiricism by suggesting that it
is not sufficiently epistemically modest: the doctrine that the aim of
science is truth about what is observable should be replaced with the
doctrine that the aim of science is truth about what’s actually been
observed. (For versions of this criticism, see for example Gutting
1985, Railton 1990, Rosen 1994, and Alspector-Kelly 2001.)

The constructive empiricist’s reply, as presented by Monton and van
Fraassen (2003, 407–408), is as follows. Constructive empiricism
incorporates a prior commitment to the rationality of science —
it is a doctrine about what the aim of science actually is; it is not
attempting to present a revisionary account of how science should be
done. According to the doctrine that the aim of science is truth about
what’s been observed,

there would be no scientific reason for someone to do an experiment
which would generate a phenomenon that had never been observed before.
But one of the hallmarks of good scientists is that they perform
experiments pushing beyond the limits of what has been observed so
far. (Monton and van Fraassen 2003, 407)

The constructive empiricist can hence conclude that the doctrine that
the aim of science is truth about what’s been observed “fails to
capture our idea of what it is to do good science” (Monton and
van Fraassen 2003, 407).

3.5 Commitments to modal realism in talk of observability?

So the constructive empiricist is firm in her construal of the aim of
science as truth about the observable. One might worry, though, as
James Ladyman (2000) does, that such a view brings with it a
commitment to modal realism and belief in whatever entities such a
commitment may require. So, for instance, talk of observability might
commit the constructive empiricist to belief in the existence of
possible worlds, a commitment that an empiricist would prefer not to
make.

To understand why one might think this way, consider the following. As
noted in section 1.6 above, one natural way of understanding
x is observable” is in the following
counterfactual manner:

x is observable iff if a suitably constituted observer were in
relevant circumstances C, she would observe x.

If the truth conditions of counterfactuals are understood in terms of
possible worlds, it is easy to see how beliefs about what is
observable entail commitments to the existence of such worlds.

One reply to this threat of modal realism is that contrary to the
initial impression provided by the counterfactual characterization of
observability, observability is not a modal property, after all
(Monton and van Fraassen 2003, 411). As explained in section 2.5
above, van Fraassen takes the truth of counterfactuals to be
context-dependent. Once a context is fixed, counterfactuals can be
expressed as non-modal conditionals. In the case of the
counterfactuals that explicate observability, then, fixing the
epistemic community of the “suitably constituted observer”
transforms the counterfactuals into straightforward non-modal
conditionals whose truth or lack thereof we can empirically
investigate (Monton and van Fraassen 2003, 413-414). Belief in the
truth of some claim of the form ‘x is observable’ amounts simply to
belief in the truth of such a context-fixed, non-modal
conditional.

Whether such conditionals are true is an empirical question to which
our best scientific theories may provide an answer. So even though
observability represents some objective, theory-independent property
of the world (van Fraassen 1980, 57), we can use our best scientific
theories to answer the question, “What is observable?”
(Monton and van Fraassen 2003, 415-416):

Consider the claim ‘if the moons of Jupiter were present to us
(in the right kind of circumstances) then we would observe
them’. The way to understand the claim is to note that, even
though it is a counterfactual, it is entailed by facts about the
world: facts that the moons of Jupiter are constituted in a certain
way, and facts that we are constituted in a certain way. These facts
can be disclosed by empirical research. In practice, not all the
empirical research has been done, so we have to rely on our current
best theories to determine what these facts are.

For worries about methodological circularity in using our accepted
theories to supply facts about observability– facts that bear on the
theories’ own empirical adequacy– see section 3.7 below.

One additional worry about Monton and van Fraassen’s non-modal
characterization of observability is given by Ladyman (2004). Consider
the claim ‘x is observable’ for some x that
is never actually observed. Ladyman asserts that no empirical
investigation will be sufficient to establish the truth of the
relevant non-modal conditional “unless we take it that the
specification by science of some regularities among the actual facts
as laws … is latching onto objective features of the
world” (Ladyman 2004, 762). As Ladyman sees it, only objectively
existing laws, and not pragmatically selected empirical regularities,
can underwrite claims about the observability of objects never
actually observed.

Paul Dicken (2007) offers another promising way for the constructive
empiricist to resist the threat of a commitment to modal realism that
is posed by talk of observability. He suggests that the constructive
empiricist take the same attitude toward the truth of observability
counterfactuals that she takes toward other claims of endorsed
scientific theories: namely, acceptance of the counterfactuals rather
than belief in them (608).

Indeed, given that observability is itself supposed to be a subject of
scientific theory (as noted above), acceptance is the natural attitude
for a constructive empiricist to take toward the counterfactuals that
explicate observability. She relies on those counterfactuals in the
way she relies on the other elements of the theories she accepts, even
(in certain contexts) talking as if the counterfactuals are true. In
this way, according to Dicken, she can make use of claims about what
is observable while at the same time being agnostic about possible
worlds whose existence is purportedly entailed by the truth of the
counterfactuals explicating observability.

3.6 Why Not Just Believe in Sense Data?

An objection related to the one from section 3.4 is the following. The
constructive empiricist errs not just in believing claims about what
is unobservable-but-not-actually-observed, but also in believing
claims about actually observed entities the likes of macroscopic
physical objects. If one really takes to heart the advice that one’s
beliefs should not extend beyond one’s evidence, then one should limit
belief to claims about the mental experiences that one is having.

A constructive empiricist might reply to the objection as follows:

Such events as experiences, and such entities as sense-data, when they
are not already understood in the framework of observable phenomena
ordinarily recognized, are theoretical entities. They are, what is
worse, the theoretical entities of an armchair psychology that cannot
even rightfully claim to be scientific. I wish merely to be agnostic
about the existence of the unobservable aspects of the world described
by science — but sense-data, I am sure, do not exist. (van
Fraassen 1980, 72)

3.7 The Hermeneutic Circle

As noted in Section 1.6 above, the constructive empiricist says that
what counts as observable is relative to who the observer is and what
epistemic community that observer is part of. Since the observer is
her- or himself the subject of scientific theory, what counts as
observable is also the subject of scientific theory. Here are two
worries about the use of scientific theory as the determiner of
observability:

Relativity: If a theory of observability determines
what is observable, and empirical adequacy is assessed in terms of
what is observable, then a theory of observability can name the terms
of its own empirical adequacy. Empirical adequacy becomes radically
relative. With no objective, theory-independent constraints on
empirical adequacy, it’s “anything goes” when it comes to
theory acceptance: one simply adopts the theory of observability that
underwrites the empirical adequacy of whichever theory one is
interested in accepting.

Circularity: if scientific theory is the arbiter of
observability, then an individual has no choice but to use the theory
of observability she accepts as a guide to observability, and hence as
a guide to empirical adequacy, and hence as a guide to whether or not
to accept that very theory. But to use the theory as a guide to
whether or not to accept that theory involves the individual in
epistemic circularity.

The constructive empiricist might reply to Relativity by insisting
that while we must look to science for an account of observability,
observability is not a theory-dependent notion. What counts as
observable is an objective, theory-independent fact. So there’s no
danger of relativism about empirical adequacy (van Fraassen 1980,
57–58).

This response only addresses Relativity; the objectivity of
observability does not save us from the epistemic circularity that
comes about from our having to use a theory of observability as the
standard of empirical adequacy by which we assess that theory’s own
empirical adequacy. The epistemic circularity has to do with how we
come to certain beliefs about observability, not with the objectivity
of the observability facts.

If such circularity were avoidable, then it would be good for us to
avoid it. Unfortunately for us, the constructive empiricist might say,
it is not avoidable (Monton and van Fraassen 2003, 415–416,
maintains this line). Advocates of constructive empiricism might
insist that any search for a Cartesian-style guarantee of the
correctness of our theory of observability is a search in vain. We
have to accept some such theory, imperfect though it may be, and
modify our acceptance if experience proves that acceptance to be
misplaced.

3.8 Observability of the Microscopic

The Hermeneutic Circle objection was prefaced on the claim that what
counts as observable is, according to the constructive empiricist,
determined by scientific theory. Another worry based on that
presupposition, raised by Alspector-Kelly (2004), is that scientific
theory determines much more to be observable than the constructive
empiricist typically allows. On Alspector-Kelly’s view, we should
countenance as observable whatever science says we can have reliable
information about on the basis of perceptual experience, and science
says we can have reliable information about what is perceptually
revealed to us via microscopes.

The electron microscope is a window on the microcosm because it
generates reliable images… We know of that reliability in virtue of
knowing the science behind it, just as the constructive empiricist
knows the limits of unaided human observation by knowing the science
behind the perceptual process. (Alspector-Kelly 2004, 347)

Given what it is for experience to provide us with information about
the world, electron microscopes and the rest do precisely that for our
community… even a relatively conservative estimation of our
perceptual abilities, concerned with both reliability and fidelity,
has them extending much farther into the microcosm than the overly
conservative constructive empiricist is willing to recognize.
(Alspector-Kelly 2004, 348)

In response to Alspector-Kelly, Kusch (2015) insists that the
constructive empiricist can rely on science to determine what counts
as observable, without at the same time countenancing the
microscopic as observable. That’s because “the phenomenon of
naked-eye observation calls for one (kind of) theory; the phenomenon
of instrumentally-aided eye-use calls for at least two (kinds of)
theories: the theory covering naked-eye observation and theories of
the instrument and its interaction with our naked eyes” (179). As
noted earlier, constructive empiricists value epistemic modesty. If a
constructive empiricist can rely on science to give us an account of
the kind of unaided observation in which all science is grounded,
without at the same time having to make use of scientific theories
that go farther afield, then by the constructive empiricist’s
lights, that more modest invocation of science is to be preferred in
deciding the question of observabillity.

3.9 Commitment to the Existence of Abstract Objects?

Rosen (1994, 164–169) contends that a scientist cannot remain
faithful both to the epistemic standards of the empiricist at the same
time that she accepts various scientific theories in the way that the
constructive empiricist describes. If what Rosen says is correct, then
constructive empiricism fails as an explanation of how a committed
empiricist can endorse the activity of science as rational.

Rosen’s argument goes as follows. Using the terminology of van
Fraassen’s semantic view of theories (described in Sec. 1.5 above),
Rosen says an individual believing a theory to be empirically
adequate

is thereby committed to at least three sorts of abstract objects:
models of the phenomena (data structures), the models that comprise
T, and functions from the one to the other. To suspend
judgment on the existence of abstract objects is therefore to suspend
judgment on whether any theory is empirically adequate, and this just
[is] to give up acceptance altogether. (166)

Indeed, we would naturally suspect that a constructive empiricist
would suspend belief about the existence of abstract objects,
which are unobservable entities if anything is. So it looks as if an
empiricist cannot accept any scientific theories, if acceptance
amounts to what the constructive empiricist says it does.

One possible response the constructive empiricist might give here is a
fictionalist account of mathematical objects. Embracing such a
fictionalist view, an individual could use the theoretical apparatus
of mathematics without committing herself to the existence of the
objects that are the alleged subject matter of mathematical theories.
Rosen (1994) considers this response but contends that it is not one
that a constructive empiricist may want to accept. The problem, Rosen
says, is that to embrace fictionalism about a theory T that
one accepts commits one to believing claims of the following form:

(T ′)   the world is such that if there were such a thing as T,
it would be empirically adequate (167).

Such a counterfactual-involving belief appears to commit the believer
to the truth of certain modal facts, a commitment eschewed by the
typical Hume-inspired empiricist. Perhaps the constructive empiricist
can view the relevant counterfactuals as reducible to non-modal
conditionals, in the spirit of the context-dependent reduction of
counterfactuals to non-modal conditionals entertained in section 3.5
above. If such a reduction can be successfully undertaken, the
constructive empiricist can avoid commitment to belief in the truth of
the relevant modal facts.

Whether the constructive empiricist would ultimately want to endorse
some fictionalist view about mathematical objects is an open question.
For an attempt at developing a constructive empiricist philosophy of
mathematics, see Bueno 1999.

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