1. What is the "empiricist consensus"?
This term is an artificial label (used for present teaching purposes)
to designate a very general position with respect to scientific knowledge.
This label is approximately synonymous with the expressions "the received
view," "the empiricist view or model," "the "positivist view or model."
All these names refer to the view of science then tended to dominate in
most (but not all) philosophy of science for roughly the first half of
this century. Insofar as those who held it tended to equate scientific
knowledge with all knowledge, we may also say it is a very broad outlook
on human knowledge in general, in other words it is a general epistemological
point of view. This perspective on the nature of knowledge also tended
to lead those who held it to accept certain general views with respect
to the nature of reality and values. In other words, while the empiricist
consensus was primarily an epistemological orientation, it tended also
to have metaphysical and axiological dimensions.
2. Who held this view?
It is important to stress that within this general consensus, there
was considerable room for diversity among philosophers. Thus one large
group of philosophers within this consensus could be labeled positivists,
or more specifically "logical positivists" or "logical empiricists," and
indeed they tended to dominate, but other philosophers, for example, Bertrand
Russell or Karl Popper, could be placed within this consensus but disagreed
sharply with the positivists.
3. How has the philosophy of science been shaped by this consensus?
Insofar as they tended to share certain assumptions, debates among philosophers
within the consensus could be considered "internal" to that consensus,
and these tended to dominate philosophy of science until the sixties. There
were always critics who stood outside the dominant consensus (e.g. Michael
Polanyi, Pierre Duhem, Alfred North Whitehead or Alexandre Koyre). However,
their disagreement with the dominant consensus could be considered "external"
to the main field of debate within philosophy of science, and was thus
largely ignored within the consensus. But ultimately disagreements and
internal problems within the consensus weakened it to the point where the
"dam broke" and the once dominant consensus became flooded with both internal
and external problems. This happened to coincide rather closely with the
publication of Thomas Kuhn's Structure of Scientific Revolutions, which
therefore often has been seen as a primary cause for the dissolution of
the consensus. It is certainly an exaggeration to regard Kuhn's book as
having "caused" the break up of the empiricist consensus, but as events
happened, its time of publication was such that debates in philosophy of
science during the breakup of the consensus often took Kuhn's work as a
point of departure.
4. What was the view of those who belonged to this consensus?
It must be emphasized that this label is being used to designate an
artificial "stereotype" which can be characterized in terms of a number
of philosophical views, each one of which could be considered an element
of this consensus. All of the elements listed below might not characterize
any one real philosopher. However virtually all of those philosophers who
clearly belong to this consensus would surely share enough of these elements
such that they all could be considered as bearing a very strong philosophical
5. What are the elements of this consensus?
In the most broad sense the consensus is a position about what one ought
to believe regarding the world as experienced by human beings. If one rejects
the view that what it is "rational to believe" is "what one ought to believe,"
one is in effect rejecting a philosophical approach to belief altogether,
presumably in favor of some other method, say, flipping a coin or believing
everything consistent with some "authority," whether in human or written
form. Since philosophers, virtually by definition, will describe as "rational"
what one ought to believe, this is a view about what it is rational to
believe with respect to the world we experience. Thus one element of the
consensus is that it is a theory of "scientific rationality."
6. What does a scientifically rational person believe?
Although "beliefs" may refer to the private psychological states of
human beings (thus allowing the possibility of "beliefs" which cannot be
expressed in language), for those who held the empiricist consensus, "beliefs"
are restricted to what can in some sense be made public (and thus open
to analysis) by being communicable in the meaningful expressions, or "sentences"
of some language. Insofar as a sentence in a "natural language" (e.g. English
of German) can be "ambiguous" or can be given different meanings, we may
be justified in believing it under one possible meaning and not justified
in believing it under another; we would have in effect two different beliefs.
Thus to members of the consensus, those beliefs which one can be justified
in believing must be statements expressed by unambiguous sentences of an
artificial "ideal" language in which all meaningful expressions can be
given precise meanings. As "scientific knowledge" may be considered the
entire body of rationally justified beliefs about the world humans experience,
another element of the consensus was its "linguistic" view that "science"
in effect refers to a very large group of "statements" expressed in a special
artificial "language" of precisely defined scientific concepts.
7. What are the possible sources of knowledge about the world experienced by human beings?
Philosophers call statements about the world we experience "synthetic" and distinguish them from those whose subject is really the meanings of terms, which are called "analytic." Some philosophers (often called "rationalists") have held that it is possible to be justified in believing statements which are about the world we experience, even though experience itself never provides adequate evidence for such statements. Such philosophers argued that "Reason" unaided by experience could justify such statements. Statements which can be thus justified independently of experience are called "a priori" and distinguished from those that can be justified only by appeal to experience, "a posteriori" or "empirical" statements. Rationalists thus hold to the possibility of justifying believing "synthetic a priori" statements.
8. What is the position of the empiricist consensus regarding the possibility of synthetic a priori knowledge?
Those who belong to the empiricist consensus commonly reject this possibility.
For them all justified belief which is not restricted to the meanings of
terms, that is, which "escapes the circle of language" and refers to "the
world," is only justified by appeal to experience. In other words, we may
say that our rational warrant for holding scientific beliefs must always
be a certain body of empirical evidence expressed in certain "observation
statement" or "basic statements" which are considered to be directly verified
by experience. Thus another element of the consensus was its commitment
to empiricism against the rationalist view that some things about the world
could be known by pure reasoning. This does not mean that the empiricist
consensus has no place for reason in determining scientific belief; far
from it, the empiricist consensus strongly holds that also scientific explanation
and prediction is made possible through deductive reasoning from both general
laws and particular observation statements expressing "initial conditions."
9. Does this mean that we are rational to believe only statements about what we can "observe" (i.e., see, hear, touch, smell or taste)?
A critical problem arises when we reflect on the fact that scientific
knowledge most obviously is not prima facie limited to what human beings
have observed, in other words scientific beliefs are not limited to what
are often called "observation statements." Scientific explanations are
often couched in terms of appeals to certain "laws of nature" which are
universal statements not about particular observations actually made by
human beings but about all or any possible observation which would be made
under specified conditions. Such statements may even be about what would
be the case under conditions which in fact never occur and possibly never
could occur ("subjunctive conditionals" or "counterfactuals"). Furthermore,
many sciences are deeply committed to explaining observable phenomena through
appeal to general statements about entities, states, or processes, which
are postulated to exist but are not in fact observed, and in many cases
not even in principle "observable." Whether honored with the label of "law
of nature" or not, all such statements which transcend what is, or could
ever be, observed, are usually called "theoretical statements." Theoretical
statements are marked by the fact that they contain one or more conceptual
terms appearing to refer to entities, states, or processes which are not
observed. Thus one of the core elements of the empiricist consensus is
that one can always distinguish between observational and theoretical statements.
Some members of the consensus may have admitted that the observational/theoretical
distinction could not be sharply drawn, but all held it to be a real and
10. Why is this observational/theoretical distinction so important?
The distinction marks a difference between why we are justified in believing
the two kinds of statements. Observation statements (also called "basic
statements" or "protocol Statements") are justified by a "direct" appeal
to experience; they are the statements of science which "reach outside"
the body of language and connect scientific beliefs directly to the world
we experience. However, theoretical statements are different; we are not
justified in believing them on such direct grounds. These statements are
treated as "hypotheses" which we are justified in believing only on the
basis of the "evidence" provided by the "observation statements." The observational/theoretical
distinction thus marks the distinction between evidence and that which
the evidence "supports," what are usually called "theories." Thus theoretical
statements are admitted into science only when they can, under specifiable
circumstances, be used to deduce directly verifiable "observation statements."
A statement about unobservable entities or processes which could not be
used to predict and observable consequences is said to have no "empirical
content" or "empirical significance" and cannot form an acceptable statement
in scientific knowledge.
11. Does the observational evidence prove the theoretical statements for which it is the evidence?
We often talk about the laws of science as having been "proved." The
word "prove" indicates that the truth of the evidence, if it is true, establishes
necessarily the truth of those statements which such evidence is said to
support. It has been widely admitted since the time of Hume that in this
sense no empirical evidence about particular observations can ever prove
the truth of a universal statement which extends beyond what is already
present in the empirical evidence. Holders of the empiricist consensus
are all "descendants of Hume" in this respect. Therefore, they can be understood
a relaxing the classical demand for certainty (necessarily true) and holding
that we are rational to believe theoretical statements which are "well-confirmed"
or "corroborated" by the empirical evidence. We express this by saying
that another element of the consensus is a commitment to "fallibilism,"
i.e., the view that no statement in science is ever immune to refutation
by some as yet unknown evidence. Fallibilists reject the view that any
theory is ever proved.
12. What is the relationship between empirical evidence and theory?
This was the topic over which defenders of the consensus spent most
of their energies. The aim of the philosophy of science, so they argued,
is to exhibit and analyze this relation, but they disagreed among themselves
radically as to the nature of this relation. Originally the hope was that
one could "reduce" or translate theoretical statements into open ended
sets of observation statements, but gradually this ideal was seen as unattainable.
Later on, some, like the positivists Carnap and Reichenbach, were most
anxious to develop a "logic of confirmation" according to which one could
assess just how probably true any universal statement would be in the light
of any particular body of empirical evidence. Others, like Popper, argued
that empirical evidence could serve only a negative role, "falsifying"
those hypotheses we ought to reject ("falsificationism"). According to
this outlook what we ought to believe is those hypotheses subject to rigorous
empirical testing which have not been refuted. Nevertheless, both the positivist
"verificationist" program and its arch rival within the dominant consensus,
the Popperian falsificationist program, both accepted some form of a "deductive-nomological
model" (or "DN Model") of scientific explanation and a "hypothetico-deductive
model" of the relation between evidence and theoretical statements.
13. What does the "deductive-nomological model" hold regarding the nature of scientific explanations?
According to this model, the aim of science is to provide explanations of particular observed phenomena by showing that the occurrence of such phenomena can be validly deduced from a collection of several theoretical statements of universal laws and other observation statements describing observable "initial" or "antecedent" conditions. When such a deduction is performed prior to the occurrence of the phenomenon, it is called a "prediction," after the phenomenon has already occurred, it is called an "explanation." However the valid deduction of a single observable phenomenon -or even a very large number of phenomena- from a law does not establish the truth of the law. To say a deduction is "valid" means only that if those laws are true then that phenomenon would occur. Laws themselves can be explained by deduction from "higher level" laws, but that, of course, does not establish the truth of those higher level laws.
14. Why are we justified in accepting such scientific explanations?
According to the "hypothetico-deductive model of justification" which
came to be an accepted element of the empiricist consensus, when observation
reveals that the predicted phenomenon occurs as predicted, the law from
which it is predicted is "confirmed," or "corroborated," when observation
reveals that phenomena do not occur as predicted, the law is "refuted"
or "falsified." Prior to any successful predictions, a theoretical statement
is purely "hypothetical." Only direct observation statements may be regarded
as "verified." Positivists came to accept that all hypotheses are only
"confirmed" by the evidence. Falsificationists emphasized that attempts
to refute the hypothesis have failed and spoke of the hypothesis as "corroborated."
After it has been confirmed by a wide range of successful predictions,
and in the absence of any falsifying failed predictions, theoretical statements
move from being of a purely "hypothetical" status to being rationally justified
and are often called "laws of nature." The difference between a "law" and
a "theoretical hypothesis" (or "conjecture") is thus merely the degree
of confirmation or corroboration.
15. How are the universal statements which become accepted as laws related to each other?
Many who belonged to the empiricist consensus held that, at least ideally,
lower level theoretical statements (whether regarded as mere "hypotheses"
or as "laws") could be explained by showing that they could be deduced
from higher level more embracing theoretical statements, until in an ideal
perfected science, all phenomena could be seen as deducible from set of
relatively few fundamental "laws of nature." The epistemic justification
for such theoretical laws, then, is seen as based upon the "foundation"
of all actual observation statements which confirm the predictions deduced
from the theory; this foundation "supports" or "rationally justifies" the
theoretical structure of scientific laws which is erected upon it. Hence
this view is said to be a form of "foundationalistic epistemology." One
could imagine that in an ideal case the body of rationally justified scientific
beliefs, a "total unified science" could be arranged as a hierarchy of
statements with the most general all embracing fundamental laws of nature
at the top and lower level, more specific laws being deduced from them
under restricted conditions, in much the same fashion that the theorems
of geometry follow from its fundamental axioms and postulates. However,
such a system of deductively interrelated theoretical statements, becomes
"science" only because the rational warrant for belief in these statements
comes not from the "top down," i.e., from axioms to theorems (as appears
to be the case in geometry), but from the "bottom up," i.e., from the empirical
observation statements which serve to confirm directly the lowest level
most particular statements deduced from the system of theoretical laws.
16. How does this epistemological outlook relate to the "scientific method"?
According to the empiricist consensus what is normally taught as the
"scientific method" is in effect those procedures which warrant the rational
acceptance of theoretical laws, i.e., the process of deducing empirical
consequences from theoretical hypotheses and statements of observable conditions,
and the confirmation or refutation of those hypotheses. This procedure
is seen as a process of "testing" hypotheses and is regarded as the primary
occupation of all science. While the methods for devising the specific
tests of individual hypotheses may vary from science to science, all sciences
share in common allegiance to this method of testing general laws by empirical
evidence as the only method for establishing the rational warrant for accepting
theoretical laws and the scientific explanations and predictions deduced
from them. Thus defenders of the consensus accepted as another element
a commitment to the "unity of science" with respect to its methodology.
17. How do we first arrive at the hypotheses which come to be accepted
as laws of nature?
What transforms a hypothesis into an accepted scientific belief is the process of testing by the hypothetico-deductive procedure indicated above. This part of the scientists' activity was often referred to as the "context of justification" and it is often distinguished from the process by which the scientist formulates the hypothesis in the first place, which is called the "context of discovery." Since only the context of justification makes a hypothesis scientific, only it is relevant to the philosophical account of the rational warrant for scientific belief. Generally members of the consensus tended to relegate the context of discovery to the personal, and often idiosyncratic psychological factors which characterized particular historical human scientists, accounts of which may be psychologically or historically interesting, but which are irrelevant to the philosophical account of how a hypothesis becomes a part of science. The philosopher is interested in the "logic" by which a scientific belief comes to be warranted, not the psychological or historical process which led to its formulation in the first place. Thus the distinction between context of justification and context of discovery was also an essential element of the empiricist consensus in philosophy of science.
18. How can change in scientific belief be explained by the consensus?
One of the most obvious aspects of science is that what today's scientists
believe differs markedly from the past, as the science of each period has
differed from that of its predecessors. Scientific belief is not static,
but continuously changing, perhaps often in extensive or revolutionary
ways. Of course it can occur that laws which were formerly well confirmed
by repeated tests, in the future get refuted by new tests, thus causing
a change in the body of empirical evidence, which may have been once favorable
but becomes unfavorable as human experience of the world grows. This is
one kind of change. But often change was understood as a case of "reducing"
more restrictive narrow hypotheses to broader more general hypotheses.
According to the consensus it was ideally possible to reconstruct the history
of any science showing that what were originally conceived as general laws
turn out to be more restricted cases of yet more general laws. (This was
especially held in the case where Galileo's mechanics was seen as a restricted
case of Newtonian mechanics and Newtonian mechanics subsequently seen as
a restricted case of Einstein's relativistic mechanics.) In this way, change
in science could be explained in terms of progress moving towards the ever
more general all-embracing fundamental laws of nature encompassing an ever
greater range of phenomena. If laws are regarded as "true" this progress
could be seen as progress towards the truth about the world we experience.
19. Are the fundamental laws true?
The word "truth" is generally taken to imply that what is true must
be about something which exists or is "real." This is often called the
"correspondence theory of truth", according to which the true statement
is true because it represents things as they really are, the "facts" correspond
to what the law says, whereas the false statement is false because it fails
to do so. According to this notion of "truth" as referring to a representational
relation between statement and reality, since all theoretical statements
go beyond the purely observable and make statements about unobservable
processes or properties or objects, perfected scientific theories are really
true descriptions of this "unobservable" world which is often said to "lie
behind the observable phenomena." This reality is often believed to stand
in some causal relation to what is observed. In short it was held by the
consensus that if one holds that such statements are true in this correspondence
sense, then one must hold that such unobservable entities are the real
causes of observable phenomena. This position is known as scientific realism.
Many defenders of the consensus were scientific realists in this sense.
However, one could accept all the elements of the consensus and argue that
only observation statements are true or false; theoretical statements are
neither true nor false, but are accepted because of their use as "instruments"
enabling the scientist to infer from one set of observation statements,
those stating the antecedent conditions, to another set of observation
statements, those describing the observed phenomenon predicted or explained.
This view, often called instrumentalism, is a specific form of "anti-realism,"
and was defended by some members of the consensus. Thus in one sense the
consensus was neutral on realism versus anti-realism, but in another sense,
namely that realism demands a commitment beyond what the consensus agreed
upon, it is fair to regard the empiricist consensus as anti-realist, at
least in spirit, though many of its defenders would have called themselves
20. Does the consensus hold that it is describing actual science?
No; defenders of the consensus held that the philosopher of science
was concerned with developing a "model" or account of an ideal perfected
science. They fully well realized that actual real sciences always fell
short, often severely, of this ideal picture of what a science should be.
But this fact merely indicates that real science is incomplete and part
of a human, historical process; thus it is heir to all the errors of which
humans are capable.
21. What is the purpose of a philosophy of science which ignores real science and concentrates on a perhaps unattainable ideal?
The function of the philosopher of science is normative; the ideal picture of science painted by the philosopher serves as a standard by which one can assess the degree to which any body of beliefs approaches what it should be to gain rational acceptability, i.e. to be "scientific knowledge." At the same time this standard enables one to distinguish the bona fide true science from pseudo-science, and thus distinguish what the scientifically rational person ought to believe from what he ought to reject. The problem of drawing the boundary between science and pseudo-science was known as the "problem of demarcation" and was a central concern of many who held the empiricist consensus.