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Wesley Salmon

Wesley C Salmon (1925 – 22 Apr 2001), a contemporary American philosopher of science, attained especial prominence for leading renewal of emphasis on causality in scientific explanation. Traditionally, scientific explanation modeled regularities via lawlike explanation, formalized as the covering law model. Salmon proposed causal-mechanical explanation, more prominent in biological sciences than in physical sciences. Salmon also proposed the criterion strict maximal specificity to supplement the covering law model's deductive-nomological model (DN model), and, as to covering law model's other component, that is, inductive-statistical model (IS model), introduced statistical-relevance model (SR model). He died in a car crash.


Salmon attended Wayne University; afterwards, he received a masters degree in 1947 from the University of Chicago.[1] He earned his PhD in philosophy from UCLA under the direction of Hans Reichenbach. Salmon taught at Indiana University Bloomington , University of Arizona, and finally at the University of Pittsburgh


A major feature of Salmon’s work consists of providing a philosophically sound basis for scientific explanation. Salmon claimed that a scientific explanation is the state of affairs of something fitting into or being a part of a pattern in the world, where the pattern is constituted by at least one causal process. A process is the real physical connection between cause and effect. For example, the heat from the flame of a gas stove excites the molecules in the water via the iron atoms in the bottom of the pan. This is a process where every step from the cause, the flame, can be traced to the effect, boiling water. This view has come to be known as the ‘ontic’ account of explanation, specifically a causal-mechanical model of explanation, which involved mechanism (biology). It is thoroughly realist and rests on an ontology that is designed to answer the question: "Just what is a causal process?"

Salmon argued that events are intersections of two or more causal processes. This interpretation leads to depicting the world as a network with lines (causal processes) and nodes (intersections of causal processes – events). Thus events, causes and effects are reduced to causal processes, where causal processes are real connections between events. According to Salmon, causal processes transmit 'structure', or energy and momentum or 'information' from one spatio-temporal location to another. There are two ways, in principle, by which it is possible to demarcate causal processes from 'pseudo-processes' – how causal processes are transmitted through space-time and what they transmit. As for how causal processes are transmitted, the theory holds that the transmissions must be continuous, with no discontinuities or 'jumps' in space-time. Unfortunately this is not enough to be sure that it is a genuinely causal process, as 'pseudo-processes' can also be continuous.

Demarcation requires that it is necessary to examine what causal processes transmit. Salmon argued causal processes transmit information, and as such we should be able to 'mark' a process by modifying it, to see if the modification is transmitted. This 'marking principal' serves to demarcate causal process from pseudo-processes, as the latter cannot be marked. Further to this, 'things' are 'causal agents' if they are originators of causal chains and not merely 'passers on' of causes. They are 'uncaused causers'. The 'uncaused causer' is the first cause in a new causal chain. It is the initial cause in the chain of causal events we are interested in explaining. The uncaused causer obviously had a cause of its own, but in terms of the phenomenon that we are attempting to explain, the uncaused causer's cause is irrelevant

Salmon's ontology of causal processes seems to fit scientific explanations very well. For example, genes are very much 'causal agents'. Geneticists have inserted the 'antifreeze' genes from flounders into the genetic code of tomatoes. This then protects the tomatoes from frost damage. A process (normal reproduction) has been marked, such that the information that is transmitted (the DNA) is modified (the addition of the flounder gene). Genes, therefore, are a part of a genuine causal process. Specifically, genes are made up of DNA. Inside the cell nucleus, a particular nitrogen-base sequence of DNA controls precisely what proteins are formed in the cytoplasm. By controlling the synthesis of proteins, DNA determines what chemical reactions take place in the cell. The chemical reactions of cells affect the chemical reactions of the body. A small chemical change to the way a particular molecule forms can produce a considerable effect on the phenotype.

Here we have a detailed account of the way genes cause phenotypic effects. DNA is information that tells the cell what kind of proteins to form. This, in turn, governs the chemical reactions in the cell, which then produces a phenotypic effect. The gene is the 'uncaused causer' in the chain of causal events we are trying to explain.

Salmon also contributed to Bayesian concepts of probability. He attempted to explain Thomas Kuhn in terms of Bayes' theorem in an article called "Rationality and Objectivity".


  • (1967) The Foundations of Scientific Inference
  • (1984) Scientific Explanation and the Causal Structure of the World
  • (1990) Four Decades of Scientific Explanation
  • (1998) Causality and Explanation
Further readings
  • Forge, J. (1999). Explanation, Quantity and Law. Aldershot: Ashgate.

External links

  • Obituary
  • Wesley C. Salmon Papers: [1](Wesley C. Salmon Papers, 1950-2001, ASP.2003.01, Archives of Scientific Philosophy, Special Collections, University of Pittsburgh.)

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