Empiricism, Semantics, and Ontology
[In this essay Carnap is concerned with the question of the "reality" of the sorts of what he calls "abstract entities" which are not the objects of direct observation. Examples of such "abstract objects" include the objects of mathematics, propositions in languages, classes, and relations between objects. While earlier positivists had wanted to ban "metaphysical" questions about the "reality" of things from meaningful discourse altogether, their attempt to "reduce" all knowledge to a foundation of observation statements about "sense data" in effect was committed to the metaphysical view that such "sense data" are the real things of which reality consists, a metaphysical view known as "phenomenalism." As positivists came to grapple with the problems of this sense data theory, they gradually moved away from their original foundationist approach of this very strong empiricistic reductionism towards a conventionalist conception of justification in terms of "linguistic constructivism."
In this late essay, Carnap shows the positivist move towards a conventionalism which holds that questions about the reality of the sorts of entities mentioned are relativized to a "linguistic framework." If one assumes a "linguistic framework" as given and asks, given this framework, are there entities of such and such a sort, then the question can be answered in a straightforward way -either empirically or logically- by determining the truth conditions of statements (i.e. the (presumably) directly verifiable statements about what is "directly observed") referring to such entities. Such questions that take the linguistic framework as given are called by Carnap "internal" questions to that framework (i.e., they are questions asked from "inside" the framework). However, if one steps "outside" the framework, and asks not whether statements referring to such entities are meaningful in this language, but whether this language is the "correct" or "true" framework which "corresponds to "reality," then one is asking what Carnap calls an "external question." Such external questions, Carnap argues, do not have a factual answer. In other words. they are neither true nor false, but they are "answered" merely in terms of whether the convention to employ such a framework is an effective means of achieving the purpose of such linguistic communication. The linguistic framework itself cannot be meaningfully said to "correspond" (or "not correspond") to "reality"; instead Carnap now tells us it "can only be judged as being more or less expedient, fruitful, conducive to the aim for which the language is intended. Judgments of this kind supply the motivation for the decision of accepting or rejecting the kind of entities."]
I. THE PROBLEM OF ABSTRACT ENTITIES
Carnap begins with the observation that reference to "abstract entities" (i.e. to what is not directly observed) appears to be unavoidable in scientific discourse, especially in physics. This is naturally problematic for the empiricist who wants to justify scientific claims to knowledge, giving the positivist a sort of "uneasy conscience":
Empiricists are in general rather suspicious with respect to any kind of abstract entities like properties, classes, relations, numbers, propositions, etc. They usually feel much more in sympathy with nominalists than with realists (in the medieval sense). As far as possible they try to avoid any reference to abstract entities and to restrict themselves to what is sometimes called a nominalistic language, i.e., one not containing such references. However, within certain scientific contexts it seems hardly possible to avoid them. In the case of mathematics, some empiricists try to find a way out by treating the whole of mathematics as a mere calculus, a formal system for which no interpretation is given or can be given. Accordingly, the mathematician is said to speak not about numbers, functions, and infinite classes, but merely about meaningless symbols and formulas manipulated according to given formal rules. In physics it is more difficult to shun the suspected entities, because the language of physics serves for the communication of reports and predictions and hence cannot be taken as a mere calculus. A physicist who is suspicious of abstract entities may perhaps try to declare a certain part of the language of physics as uninterpreted and uninterpretable, that part which refers to real numbers as space-time coordinates or as values of physical magnitudes, to functions, limits, etc. More probably he will just speak about all these things like anybody else but with an uneasy conscience, like a man who in his everyday life does with qualms many things which are not in accord with the high moral principles he professes on Sundays. Recently the problem of abstract entities has arisen again in connection with semantics, the theory of meaning and truth. Some semanticists say that certain expressions designate certain entities, and among these designated entities they include not only concrete material things but also abstract entities, e.g., properties as designated by predicates and propositions as designated by sentences.', Others object strongly to this procedure as violating the basic principles of empiricism and leading back to a metaphysical ontology of the Platonic kind.
Carnap reveals that his purpose is to relativize such questions to a language, and that this approach does not require the sort of "Platonic ontology" which assigns to such "abstract entities" a "reality" beyond the empirical world, but is "perfectly compatible" with the empiricist/positivist account of knowledge. Thus he hope to help epiricists who find it necessary to refer to such abstract entities in their scientific claims, as must all use of mathematics, to "overcome" their "nominalistic scruples":
It is the purpose of this article to clarify this controversial issue. The nature and implications of the acceptance of a language referring to abstract entities will first be discussed in general; it will be shown that using such a language does not imply embracing a Platonic ontology but is perfectly compatible with empiricism and strictly scientific thinking. Then the special question of the role of abstract entities in semantics will be discussed. It is hoped that the clarification of the issue will be useful to those who would like to accept abstract entities in their work in mathematics, physics, semantics, or any other field; it may help them to overcome nominalistic scruples.
2. LINGUISTIC FRAMEWORKS
Carnap now makes his key distinction between internal and external questions, to which I referred above. [Be sure you understand this distinction]:
Are there properties, classes, numbers, propositions? In order to understand more clearly the nature of these and related problems it is above all necessary to recognize a fundamental distinction between two kinds of questions concerning the existence or reality of entities. If someone wishes to speak in his language about a new kind of entities, he has to introduce a system of new ways of speaking, subject to new rules; we shall call this procedure the construction of a linguistic framework for the new entities in question. And now we must distinguish two kinds of questions of existence: first, questions of the existence of certain entities of the new kind within the framework; we call them internal questions; and second, questions concerning the existence or reality of the system of entities as a whole, called external questions. Internal questions and possible answers to them are formulated with the help of the new forms of expressions. The answers may be found either by purely logical methods or by empirical methods, depending upon whether the framework is a logical or a factual one. An external question is of a problematic character which is in need of closer examination.
One linguistic framework one might adopt, the one which is in fact the one ordinarily adopted both by Carnap and everyone who uses "everyday language," is what Carnap calls the "thing language" which refers to "observable things and events." Questions about the reality of things within this language, i.e. internal questions, are settled empirically:
The world of things
Let us consider as an example the simplest kind of entities dealt with in the everyday language: the spatio-temporally ordered system of observable things and events. Once we have accepted the thing language with its framework for things, we can raise and answer internal questions, e.g., "Is there a white piece of paper on my desk?," "Did King Arthur actually live?," "Are unicorns and centaurs real or merely imaginary?," and the like. These questions are to be answered by empirical investigations. Results of observations are evaluated according to certain rules as confirming or disconfirming evidence for possible answers. (This evaluation is usually carried out, of course, as a matter of habit rather than a deliberate, rational procedure. But it is possible, in a rational reconstruction, to lay down explicit rules for the evaluation. This is one of the main tasks of a pure, as distinguished from a psychological, epistemology.) The concept of reality occurring in these internal questions is an empirical, scientific, non-metaphysical concept. To recognize something as a real thing or event means to succeed in incorporating it into the system of things at a particular space-time position so that it fits together with the other things recognized as real, according to the rules of the framework.
However, if we attempt to ask "external questions" about the "reality" of the thing world itself, the sort of question the metaphysician as opposed to the ordinary language user asks, we generate an insoluble metaphysical puzzle, which realists and idealists try to answer in their opposing ways. The position that Carnap defends now is not that such disputes are meaningless, but are to recongized as practical questions about the choice of a linguistic framework:
From these questions we must distinguish the external question of the reality of the thing world itself. In contrast to the former question, this question is raised neither by the man in the street nor by scientists, but only by philosophers. Realists give an affirmative answer, subjective idealists a negative one, and the controversy goes on for centuries without ever being solved. And it cannot be solved because it is framed in a wrong way. To be real in the scientific sense means to be an element of the system; hence this concept cannot be meaningfully applied to the system itself. Those who raise the question of the reality of the thing world itself have perhaps in mind not a theoretical question as their formulation seems to suggest, but rather a practical question, a matter of a practical decision concerning the structure of our language. We have to make the choice whether or not to accept and use the forms of expression in the framework in question.
Our "choice" to "accept" the thing language is not made deliberately, but is something we have grown up with; it is because of our mutual acceptance (for the most part) of this thing language that we are able to communicate succesfully. To be committed to a choice of a particular linguistic framework is equivalent to accepting certain linguistic rules for how to talk about the world:
In the case of this particular example, there is usually no deliberate choice because we all have accepted the thing language early in our lives as a matter of course. Nevertheless, we may regard it as a matter of decision in this sense: we are free to choose to continue using the thing language or not; in the latter case we could restrict ourselves to a language of sense-data and other "phenomenal" entities, or construct an alternative to the customary thing language with another structure or, finally, we could refrain from speaking. If someone decides to accept the thing language, there is no objection against saying that he has accepted the world of things. But this must not be interpreted as if it meant his acceptance of a belief in the reality of the thing world; there is no such belief or assertion or assumption, because it is not a theoretical question. To accept the thing world means nothing, more than to accept a certain form of language, in other words, to accept rules for forming statements and for testing, accepting, or rejecting them. The acceptance of the thing language leads on the basis of observations made, also to the acceptance, belief, and assertion of certain statements. But the thesis of the reality of the thing world cannot be among these statements, because it cannot be formulated in the thing language or, it seems, in any other theoretical language.
Now Carnap lists specifically the sorts of pragmatic features that might lead one to choose a linguistic framework: efficiency, fruitfulness, and simplicity, and based "on the content of one's experiences." Pragmatic "acceptance" of a linguistic framework is not equivalent to saying :
The decision of accepting the thing language, although itself not of a cognitive nature, will nevertheless usually be influenced by theoretical knowledge, just like any other deliberate decision concerning the acceptance of linguistic or other rules. The purposes for which the language is intended to be used, for instance, the purpose of communicating factual knowledge, will determine which factors are relevant for the decision. The efficiency, fruitfulness, and simplicity of the use of the thing language may be among the decisive factors. And the questions concerning these qualities are indeed of a theoretical nature. But these questions cannot be identified with the question of realism. They are not yes-no questions but questions of degree. The thing language in the customary form works indeed with a high degree of efficiency for most purposes of everyday life. This is a matter of fact, based upon the content of our experiences. However, it would be wrong to describe this situation by saying: "The fact of the efficiency of the thing language is confirming evidence for the reality of the thing world"; we should rather say instead: "This fact makes it advisable to accept the thing language."
Carnap now turns to contrast to the "thing language" which has empirical content, with a different "language," the linguistic framework of "the system of numbers" employed by mathematicians for purely logical purposes; propositions (theorems) in this language are what would be considered "analytic a priori" statements, whose truth or falsity is determined not empirically but by logical demonstration or proof:
The system of numbers
As an example of a system which is of a logical rather than a factual nature let us take the system of natural numbers. The framework for this system is constructed by introducing into the language new expressions with suitable rules: (1) numerals like "five" and sentence forms like
"there are five books on the table"; (2) the general term "number" for the new entities, and sentence forms like "five is a number"; (3) expressions for properties of numbers (e.g., "odd", "prime"), relations (e.g., "greater than"), and functions (e.g., "plus"), and sentence forms like "two plus three is five"; (4) numerical variables ("m", "n", etc.) and quantifiers for universal sentences ("for every n, . . .") and existential sentences ("there is an n such thatů") with the customary deductive rules.
In contrast to the thing language, from within the system of numbers, the internal question of whether a number satisfying certain conditions exists or not, is established by logical, rather than empirical means:
Here again there are internal questions. e.g., "Is there a prime number greater than a hundred?" Here, however, the answers are found, not by empirical investigation based on observations, but by logical analysis based on the rules for the new expressions. Therefore the answers are here analytic, i.e., logically true.
In contrast to the internal question, the extenal question asking about the reality of numbers apart from the linguistic framework is "metaphysical" (in pejorative sense of positivists) in that there are no empirical conditions by which such a question could be answered (or in other words it is "unverifiable"), such questions are therefore "without cognitive content" (i.e. "meaningless"):
What is now the nature of the philosophical question concerning the existence or reality of numbers? To begin with, there is the internal question which, together with the affirmative answer, can be formulated in the new terms, say, by "There are numbers" or, more explicitly, "There is an n such that n is a number." This statement follows from the analytic statement "five is a number" and is therefore itself analytic. Moreover, it is rather trivial (in contradistinction to a statement like "There is a prime number greater than a million," which is likewise analytic but far from trivial), because it does not say more than that the new system is not empty; but this is immediately seen from the rule which states that words like "five" are substitutable for the new variables. Therefore nobody who meant the question "Are there numbers?" in the internal sense would either assert or even seriously consider a negative answer. This makes it plausible to assume that those philosophers who treat the question of the existence of numbers as a serious philosophical problem, and offer lengthy arguments on either side, do not have in mind the internal question. And, indeed, if we were to ask them: "Do you mean the question as to whether the framework of numbers, if we were to accept it, would be found to he empty or not?," they would probably reply; "Not at all, we mean a question prior to the acceptance of the new framework." They might try to explain what they mean by saying that it is a question of the ontological status of numbers; the question whether or not numbers have a certain metaphysical characteristic called reality (but a kind of ideal reality, different from the material reality of the thing world) or subsistence or status of "independent entities." Unfortunately, these philosophers have so far not given a formulation of their question in terms of the common scientific language. Therefore our judgment must be that they have
not succeeded in giving to the external questions and to the possible answers any cognitive content. Unless and until they supply a clear cognitive interpretation, we are justified in our suspicion that their question is a pseudo-question, that is, one disguised in the form of a theoretical question while in fact it is non-theoretical; in the present case it is the practical problem whether or not to incorporate into the language the new linguistic forms which constitute the framework 'of numbers.
Now Carnap turns his attention to a third linguistic framework employed by logic, the "propositional framework". In what sense can we say there are "propositions"? Again we need to distinguish the internal question from the external:
The system of propositions
New variables, "p", "q", etc., are introduced with a rule to the effect that any (declarative) sentence may be substituted for a variable of this kind; this includes, in addition to the sentences of the original thing language, also all general sentences with variables of any kind which may have been introduced into the language. Further, the general term "proposition" is introduced. "p is a proposition" may be defined by "p or not p" (or by any other sentence form yielding only analytic sentences). Therefore, every sentence of the form ". . . is a proposition" (where any sentence may stand in the place of the dots) is analytic. This holds, for example, for the sentence:
(a) "Chicago is large is a proposition."
(We disregard here the fact that the rules of English grammar require not a sentence but a that-clause as the subject of another sentence; accordingly, instead of (a) we should have to say "That Chicago is large is a proposition.") Predicates may be admitted whose argument expressions are sentences; these predicates may be either extensional (e.g., the customary truth- functional connectives) or not (e.g., modal predicates like "possible", "necessary", etc.).
With the help of the new variables, general sentences may be formed, e.g.,
(c) and (d) are internal assertions of existence. The statement "There are propositions" may be meant in the sense of (d); in this case it is analytic, (since it follows from (a)) and even trivial. If, however, the statement is meant in an external sense, then it is non-cognitive. (b) "For every p, either p or not-p.
(c) "There is a p such that p is not necessary and not-p is not necessary."
(d) "There is a p such that p is a proposition."
It is important to notice that the system of rules for the linguistic expressions of the propositional framework (of which only a few rules have here been briefly indicated) is sufficient for the introduction of the framework. Any further explanations as to the nature of the propositions (i.e., the elements of the system indicated, the values of the variables "p", "q", etc.) are theoretically unnecessary because, if correct, they follow from the rules. For example, are propositions mental events (as in Russell's theory)? A took at the rules shows us that they are not, because otherwise existential statements would be of the form: "if the mental state of the person in question fulfills such and such conditions, then there is a p such that . . .". The fact that no references to mental conditions occur in existential statements (like (c), (d), etc.) shows that propositions are not mental entities. Further, a statement of the existence of linguistic entities (e.g., expressions, classes of expressions, etc.) must contain a reference to a language. The fact that no such reference occurs in the existential statements here, shows that propositions are not linguistic entities. The fact that in these statements no reference to a subject (an observer or knower) occurs (nothing like: "There is a p which is necessary for Mr. X"), shows that the propositions (and their properties, like necessity, etc.) are not subjective. Although characterizations of these or similar kinds are, strictly speaking, unnecessary, they may nevertheless be practically useful. If they are given, they should be understood, not as ingredient parts of the system, but merely as marginal notes with the purpose of supplying to the reader helpful hints or convenient pictorial associations which may make his learning of the use of the expressions easier than the bare system of the rules would do. Such a characterization is analogous to an extrasystematic explanation which a physicist sometimes gives to the beginner. He might, for example, tell him to imagine the atoms of a gas as small balls rushing around with great speed, or the electromagnetic field and its oscillations as quasi-elastic tensions and vibrations in an ether. In fact, however, all that can accurately be said about atoms or the field is implicitly contained in the physical laws of the theories in question.
Carnap now uses his distinction between "internal" and "external" questions to address the traditional philosophical "problem of universals," which originated with Plato (and led him to his theory of forms). Philosophers have worried over the "reality" of "universals," such as "red." These worries have led some (like Plato) to assert that such "universals" have a reality of their own; these abstract entities are the things to which common nouns (or adjectives) refer. Carnap shows how from his point of view these questions are solved by distinguishing internal from external questions.
The system of thing properties
The thing language contains words like "red," "hard," "stone," "house," etc., which are used for describing what things are like. Now we may introduce new variables, say "f ," "g, " etc., for which those words are substitutable and further- more the general term "property." New rules are laid down which admit sentences like "Red is a property," "Red is a color," "These two pieces of paper have at least one color in common" (i.e., "There is an f such that f is a color, and . . ."). The last sentence is an internal assertion. It is of an empirical factual nature. However, the external statement, the philosophical statement of the reality of properties -a special case of the thesis of the reality of universals- is devoid of cognitive content.
Similar considerations apply to numbers and the spatio-temporal co-ordinate system of points, especially as employed in mathematical physics.
The systems of integers and rational numbers
Into a language containing the framework of natural numbers we may introduce first the (positive and negative) integers as relations among natural numbers and then the rational numbers as relations among integers. This involves introducing new types of variables, expressions substitutable for them, and the general terms "integer" and "rational number."
The system of real numbers
On the basis of the rational numbers, the real numbers may be introduced as classes of a special kind (segments) of rational numbers (according to the method developed by Dedekind and Frege).
Here again a new type of variables is introduced, expressions substitutable for them (e.g., "[the square root of two]"), and the general term "real number."
The spatio-temporal coordinate system for physics
The new entities are the space-time points. Each is, an ordered quadruple of four real numbers, called its coordinates, consisting of three spatial and one temporal coordinates. The physical state of spatio-temporal point or region is described either with the help of qualitative predicates, or by ascribing numbers as values of a physical magnitude (e.g., mass, temperature, and the like). The step from, the system of things (which does not contain space-time points but only extended object with spatial and temporal relations between them) to the physical coordinate system is again a matter of decision. Our choice of certain features, although itself not theoretical, is suggested by theoretical knowledge, either logical or factual. For example, the choice of real numbers rather than rational numbers or integers as coordinates is not much influenced by the facts of experience but mainly due to considerations of mathematical simplicity. The restriction to rational coordinates would not be in conflict with any experimental knowledge we have, because the result of any measurement is a rational number. However, it would prevent the use of ordinary geometry (which says, e.g., that the diagonal of a square with the side 1 has the irrational value [the square root of 2]) and thus lead to great complications. On the other hand, the decision to use three rather than two or four spatial coordinates is strongly suggested, but still not forced upon us, by the result of common observations. If certain events allegedly observed in spiritualistic seances, e.g., a ball moving out of a sealed box, were confirmed beyond any reasonable doubt, it might seem advisable to use four spatial coordinates. Internal questions are here, in general, empirical questions to be answered by empirical investigations. On the other hand, the external questions of the reality of physical space and physical time are pseudo-questions. A question like "Are there (really) space-time points?" is ambiguous. It may be meant as an internal question; then the affirmative answer is, of course, analytic and trivial. Or it may be meant in the external sense: "Shall we introduce such and such forms into our language?"; in this case it is not a theoretical but a practical question, a matter of decision rather than assertion, and hence the proposed formulation would be misleading. Or finally, it may be meant in the following sense: "Are our experiences such that the use of the linguistic forms in questions will be expedient and fruitful?" This is a theoretical question of a factual, empirical nature. But it concerns a matter of degree; therefore a formulation in the form "real or not?" would be inadequate.
When we "accept" a framework, we are committing ourselves to the reality of those entities within the framework, but that choice of framework is not made because it is the "true" framework which really corresponds to how things are. Instead, acceptance of a framework is based on pragmatic considerations. Here pragmatism and positivism meet at a kind of conventionalism:
3. WHAT DOES ACCEPTANCE OF A KIND OF ENTITIES MEAN?
Let us now summarize the essential characteristics of situations involving the introduction of a new kind of entities, characteristics which are common to the various examples outlined above.
The acceptance of a new kind of entities is represented in the language by the introduction, of a framework of new forms of expressions to be used according to a new set of rules. There may be new names for particular entities of the kind in question; but some such names may already occur in the language before the introduction of the new framework. (Thus, for example, the thing language, certainly words of the type of "blue" and "house" before the framework of properties is introduced; and it may contain words like "ten" in sentences of the form "I have ten fingers" before the framework of numbers is introduced.) The latter fact shows that the occurrence of constants of the type in question -regarded as names of entities of the new kind after the new framework is introduced- is not a sure sign of the acceptance of the new kind of entities. Therefore the introduction of such constants is not to be regarded as an essential step in the introduction of the framework. The two essential steps are rather the following. First, the introduction of a general term, a predicate of higher level, for the new kind of entities, permitting us to say of any particular entity that it belongs to this kind (e.g., "Red is a property," "Five is a number"). Second, the introduction of variables of the new type. The new entities are values of these variables; the constants (and the closed compound expressions, if any) are substitutable for the variables. With the help of the variables, general sentences concerning the new entities can be formulated.
After the new forms are introduced into the language, it is possible to formulate with their help internal questions and possible answers to them. A question of this kind may be either empirical, or logical; accordingly a true answer is -either factually true or, analytic.
Carnap now proceeds to his basic conclusion; the following is hhis best statement of the difference between internal and external questions, and how each type is to be answered:
From the internal questions we must clearly distinguish external questions, i.e., philosophical questions concerning the existence or reality of the total system of the new entities. Many philosophers regard a question of this kind as an ontological question which must be raised and answered before the introduction of the new language forms. The latter introduction, they believe, is legitimate only if it can be justified by an ontological insight supplying an affirmative answer to the question of reality. In contrast to this view, we take the position that the new ways of speaking does not need any theoretical justification because it does not imply any assertion of reality. We may still speak (and have done so) of the "the acceptance of the new entities" since this form of speech is customary: but one must keep in mind that this phrase does not mean for us anything more than acceptance of the new framework, i.e. of the new linguistic forms. Above all, it must not be interpreted as referring to an assumption, belief, or assertion of "the reality of the entities." There is no such assertion. An alleged statement of the reality of the system of entities is a pseudo-statement without cognitive content. To be sure, we have to face at this point an important question; but it is a practical, not a theoretical question; it is the question of whether or not to accept the new linguistic forms. The acceptance cannot be judged as being either true or false because it is not an assertion. It can only be judged as being more or less expedient, fruitful, conducive to the aim for which the language is intended. Judgments of this kind supply the motivation for the decision of accepting or rejecting the kind of entities.
Failure to heed Carnap's distinction here between internal and external questions is what has led philosophers like Plato to assert the reality of super-empirical entities:
Thus it is clear that the acceptance of a linguistic framework must not be regarded as implying a metaphysical doctrine concerning the reality of the entities in question. It seems to me due to a neglect of this important distinction that some contemporary nominalists label the admission of variables of abstract types as 'Platonism." This is, to say the least, an extremely misleading terminology. It leads to the absurd consequence, that the position of everybody who accepts the language of physics with its real number variables (as a language of communication, not merely as a calculus) would be called Platonistic, even if he is a strict empiricist who rejects Platonic metaphysics.
Carnap concludes by attributing the view that "external questions" are meaningless to the founders of positivism movement , as well as to young Wittgenstein. (But we could just as well find it in C.I. Lewis's pragmatism of the late 1930's; so here we see American prgamatism and German positivism arriving at a common relativistic conventionalism; Carnap had emigrated to America by the time he wrote this essay.)
A brief historical remark may here be inserted. The non-cognitive character of the questions which we have called here external questions was -recognized and emphasized already by the Vienna Circle under the leadership of Moritz Schlick, the group from which the movement of logical empiricism originated. Influenced by ideas of Ludwig Wittgenstein, the Circle rejected both the thesis of the reality of the external world and the thesis of its irreality as pseudo-statements, the same was the case for both the reality of universals (abstract entities, in our present terminology) and the nominalistic thesis that they are not real and that their alleged names are not names of anything but merely flatus vocis. (It is obvious that the apparent negation of a pseudo-statement must also be a pseudo-statement.) It is therefore not correct to classify the members of the Vienna Circle as nominalists, as is sometimes done. However, if we look at the basic anti-metaphysical and pro-scientific attitude of most nominalists (and the same holds for many materialists and realists in the modern sense), disregarding their occasional pseudo-theoretical formulations, then it is, of course, true to say that the Vienna Circle was much closer to those philosophers than to their opponents.
Copyright 0 1950 by Revue Internationale de Philosophie. Re-printed by permission, from Revue Internationale de Philosophie 4 (1950), 20-40.