Hempel is sympathetic to the positivist attempts at defining cognitive significance in terms of experiential implications, but has doubts about the definability of the. by Carl G. Hempel. 1. Introduction rion of cognitive meaning, or of cognitive significance, many and of the empiricist meaning criterion provide no more. that the general intent of the empiricist criterion of meaning is basically sound, hempel mainly the second of the two distinctions ; in regard to the first,. I shall have to (A) If under a given criterion of cognitive significance, a sen tence N is.

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Carl Hempel, a German-born philosopher who immigrated to the United States, was one of the prominent philosophers of science in the twentieth century. His paradox of the ravens—as an illustration of the paradoxes of confirmation—has been a constant challenge cognitivs theories of confirmation. Together with Paul Oppenheim, he proposed a quantitative account of degrees of confirmation of hypotheses by evidence.

His deductive-nomological model of scientific explanation put explanations on the same logical footing as predictions; they are both deductive arguments. Hempel also proposed a quantitative measure of the power of a theory to systematize its data. Later in his life, Hempel abandoned the project of an inductive logic. He also emphasized the problems with logical positivism logical empiricismespecially those concerning the verifiability criterion.

Hempel studied mathematics, physics, and philosophy in Gottingen, Heidelberg, Vienna, and Berlin. In Vienna, he attended some of the meetings of the Vienna Circle. One of the leading members of logical positivism, he was born in Oranienburg, Germany, in Between March 17 and 24,Hempel gave an interview to Richard Nolan; the text of that interview was published for the first time in in Italian translation Hempel, “Autobiografia intellettuale” in Oltre il positivismo logicoArmando: This interview is the main source of the following biographical notes.

Hempel studied at the Realgymnasium at Berlin and, inhe was admitted at the University of Gottingen where he studied mathematics with David Hilbert and Edmund Landau and symbolic logic with Heinrich Behmann. The same year he moved to the University of Heidelberg, where he studied mathematics, physics, and philosophy. FromHempel studied at Berlin, where he met Reichenbach who introduced him to the Berlin Circle. He studied physics with Max Planck and logic with von Neumann. InHempel took part in the first congress on scientific philosophy organized by logical positivists.

He meet Carnap and—very impressed by Carnap—moved to Vienna where he attended three courses with Carnap, Schlick, and Waismann, and took part in the meetings of the Vienna Circle. In the same years, Hempel qualified as teacher in the secondary school and eventually, inhe gained the doctorate in philosophy at Berlin, with a dissertation on the theory of probability.

In the same year, he immigrated to Belgium, with the help of a friend of Reichenbach, Paul Oppenheim Reichenbach introduced Hempel to Oppenheim in Two years later, Hempel and Oppenheim published the book Der Typusbegriff im Lichte der neuen Logik on the logical theory of classifier, comparative and metric scientific concepts.

After another brief period in Belgium, Hempel immigrated to the United States in In those years, he was interested in the theory of confirmation and explanation, and published several articles on that subject: Oppenheim in Philosophy of Science15, Between andHempel taught at Yale University.

Fromhe taught at the University of Princeton. Aspects of Scientific Explanation and Philosophy of Natural Science were published in and respectively. After the pensionable age, he continued teaching at Berkley, Irvine, Jerusalem, and, from toat Pittsburgh.

In the meantime, his philosophical perspective was changing and he detached from logical positivism: Laudan; “Provisoes: However, he remained affectionately joined to logical positivism.

Inhe undertook the editorship with W. Essler of the new series of the journal Erkenntnis. A scientific explanation of a fact is a deduction of a statement called the explanandum that describes the fact we want to explain; the premises called the explanans are scientific laws and suitable initial conditions.

For an explanation to be acceptable, the explanans must empkricist true. According to the deductive-nomological model, the explanation of a fact is thus reduced to a logical relationship between statements: This is coghitive common method in the philosophy of logical positivism. Pragmatic aspects of explanation are not taken into consideration. Another feature is that an explanation requires scientific laws; facts are explained when they are subsumed under laws.

So the question arises about the nature of a scientific law. According to Hempel and Oppenheim, a fundamental theory is defined as a true statement whose quantifiers are not removable that is, a fundamental theory is not equivalent to a statement without quantifiersand which do not contain individual constants. Every generalized statement which is a logical consequence of a fundamental theory is a derived theory. The underlying idea for this definition is that a scientific theory deals with general properties expressed by universal statements.

References to specific space-time regions or to individual things are not allowed. But there are laws e. Therefore, there is a distinction between a fundamental theory, which is universal without restrictions, and a derived theory that can contain a reference to individual objects.

Note that it is required that theories are true; implicitly, this means that scientific laws are not tools to make predictions, but they are genuine statements that describe the world—a realistic point of view. There is another intriguing characteristic of the Hempel-Oppenheim model, which is that explanation and prediction have exactly hrmpel same logical structure: Finally, the deductive-nomological model accounts also for the explanation of laws; in that case, the explanandum is a scientific law and can be proved with the help of other scientific laws.

Aspects of Scientific Explanationpublished infaces the problem of inductive explanation, in which the explanans include statistical laws. According to Hempel, in such kind of explanation the explanans give only a high degree of probability to the explanandum hepel, which is not sifnificance logical consequence of the premises.

The following is a very simple example. The relative frequency of P with respect to Q is r The object a belongs to P Thus, a belongs to Q.

The conclusion ” a belongs to Q ” is not certain, for it is not a logical consequence of the two premises. According to Hempel, this explanation gives a degree of probability r to the conclusion. Note that the inductive explanation requires a covering law: But now the laws are not deterministic; statistical laws are admissible. However, in many respects the inductive explanation is similar to the deductive explanation.

During his research on confirmation, Hempel formulated the so-called paradoxes of confirmation. Now suppose R x means ” x is a raven” and B x means ” x is black. In his monograph Fundamentals of Concept Formation in Empirical ScienceHempel describes the methods according to which physical quantities are defined.

Hempel uses the example of the measurement of mass. An equal-armed balance is used to determine when two bodies have the same mass and when the mass of a body is greater than the mass of the other. Two bodies have the same mass if, when they are on the pans, the balance remains in equilibrium.

If a pan goes down and the other up, then the body in the lowest pan has a greater mass. From a logical point of view, this procedure defines two relations, say E and Gso that:. The second step consists in defining a function m which satisfies the following three conditions:. Conditions 1 – 7 describe the measurement not only of mass but also of length, of time and of every extensive physical quantity.

A quantity is extensive if there is an operation which combines the objects according to condition 7, otherwise it is intensive ; temperature, for example, is intensive. According to Hempel, there is an implicit assumption in neopositivist analysis of science, namely that the meaning of theoretical terms can be explained by means of linguistic methods.

Therefore, the very problem is how can a set of statements be determined that gives a meaning to theoretical terms.

Hempel analyzes the various theories proposed by logical positivism. According to Schlick, the meaning of theoretical concepts is determined by the axioms of the theory; the axioms thus play the role of implicit definitions. Therefore, theoretical terms must be interpreted in a way that makes the theory true. But according to such interpretation—Hempel objects—a scientific theory is always true, for it is true by convention, and thus every scientific theory is a priori true.

Also the thesis which asserts that the meaning of a theoretical term depends on the theory in which that term is used is, according to Hempel, untenable.

### Carl Hempel (Stanford Encyclopedia of Philosophy)

Another solution to the problem of the meaning of theoretical terms is based on the rules of correspondence also known as meaning postulates. They are statements in which observational and theoretical terms occur.

Theoretical terms thus gain a partial interpretation by means of observational terms. Hempel raises two objections to this theory. First, he asserts that observational concepts do not exist. When a scientific theory introduces new theoretical terms, they are linked with other old theoretical terms that usually belong to another already consolidated scientific theory.

Therefore, the interpretation of new theoretical terms is not based on observational terms but it is given by other theoretical terms that, in a sense, are more familiar than the new ones.

## Carl Gustav Hempel (1905—1997)

The crkteria objection is about the conventional nature of rules of correspondence. A meaning postulate defines the meaning of a concept and therefore, from a logical point of view, it must be true.

But every statement in a scientific theory is falsifiable, and thus there is no scientific statement which is beyond the jurisdiction of experience.

So, a meaning postulate can be false as well; hence, it is not conventional and thus it does not define the meaning of a concept but it is a genuine physical hypothesis. Meaning postulates do not exist. It is very interesting that a philosopher who is famous for his deductive model of scientific explanation criticized the deductive model of science.

At least this fact shows the open views of Hempel. He argues that it is impossible to derive observational statements from a scientific theory. Without such hypothesis, it is impossible to apply the theory to the study of planetary motion.

But this assumption does not belong to the theory.

## Carl Hempel

Therefore, the position of planets is not determined by the theory, but it is implied by the theory plus appropriate assumptions. Accordingly, not only observational statements are not entailed by the theory, but also there are no deductive links between observational statements.

Hence, it is impossible that an observational statement is a logical consequence of a theory unless the statement is logically true. This fact has very important consequences. One of them is that the empirical content of a theory does not exist. Neopositivists defined it as the class of significanve statements implied by the theory; but this class is an empty cogniitve.