Carl Gustav "Peter" Hempel (January 8, 1905 in Oranienburg, Germany - November 9, 1997 in Princeton, New Jersey) was a philosopher of science and a major figure in 20th-century logical empiricism. He is especially well known for his articulation of the Deductive-nomological model of scientific explanation, which was considered the "standard model"
"The explanans falls into two subclasses; one of these contains certain sentences Cl, C2,..., Ck which state specific antecedent conditions; the other is a set of sentences L1, l2..., Lr, which represent general laws."
His deductive-nomological model of scientific explanation put explanations on the same logical footing as predictions; they are both deductive arguments. The difference is a matter of pragmatics, namely that in an explanation the argument’s conclusion is intended to be assumed true whereas in a prediction the intention is make a convincing case for the conclusion.
"If the proposed explanation is to be sound, its constituents have to satisfy certain conditions of adequacy, which may be divided into logical and empirical conditions." "1) The explanandum must be a logical consequence of the explanans; in other words, the explanandum must be logically deducible from the information contained in the explanans; for otherwise, the explanans would not constitute adequate grounds for the explanandum." "2) The explanans must contain general laws, and these must actually be required for the derication of the explanandum." "3) The explanans must have empirical content; i.e., it must be capable, at least in principle, of test by experiment or observation."
"Our characterization of scientific explanation is so far based on a study of cases taken from the physical sciences. But the general principles thus obtained apply also outside this area. Thus, various types of behavior in laboratory animals and in human subjects are explained in psychology by subsumption under laws or even general theories of learning or conditioning; and while fre-
quently, the regularities invoked cannot be stated with the same generality and precision as in physics or chemistry, it is clear, at least, that the general character of those explanations conforms to our earlier characterization.
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 quantifiers), and 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.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.
Problems for the Covering-Law Model: Some counterexamples seem to show that an "explanation" could satisfy all of the criteria listed even though the explanatory information was completely irrelevant to the explanandum. Other counterexamples apparently show that an "explanation" could satisfy all the criteria, and be relevant, and yet fail to constitute a genuine explanation. This is because of what is sometimes called the symmetry of D-N explanation.
He was the last surviving member of the Vienna Circle, a group of philosophers who loathed the irrational and mystical thinking of late-19th-century Europe and, in reaction, advocated what they called ''logical positivism,'' which argued that whatever could not be verified by experience was meaningless.
Hempel came to believe that the application of symbolic logic held the key to resolving a broad range of problems in philosophy, including that of separating genuine problems from merely apparent ones. Hempel's commitment to rigorous explications of the nature of cognitive significance, of scientific explanation, and of scientific rationality would become the hallmark of his research, which exerted great influence on professional philosophers, especially during the middle decades of the 20th Century.
A generation ago, Hempel's covering-law models of scientific explanation were widely accepted among philosophers of science. One of the critics who has been most active in dissolving this consensus is Wesley Salmon.
"To explain the phenomena in the world of our experience, to answer the question "why" rather than only the question "what?" is one of the foremost objectives of empirical science." "[In The Basic Pattern of Scientific Explanation] we divide an explanation into two major constituents, the explanandum and the explanans. By the explanandum, we understand the sentence describing the phenomenon to be explained (not that phenomenon itself); by explanans, the class of those sentences which are adduced to account for the phenomenon."
According to Hempel the objective of empirical science is to explain the sentences describingphenomena; specifically to explain the phenomena (the event that happens) in the world of experience."The objective is to answer the question of “why?” rather than only “what?” " [thus dismissing metaphysics]; this is consistent with logical positivism.