University of Minnesota

Sir Peter Medawar on the Nature of Scientific Thought, Process, and Writing

Peter Medawar, 1960 Nobelist, criticizes the format of science writing as based on John Stuart Mills’ mistaken ideas about inductive reasoning in science. For example, Medawar claims that the discussion should come first in a paper, rather than arising from the results. In a radio broadcast: “Is the scientific paper a fraud?” (1964 BBC), he means that “the scientific paper may be a fraud because it misrepresents the processes of thought that accompany or give rise to the work that is described in the paper.” The scientific paper embodies “a totally mistaken concept, even a travesty, of the nature of scientific thought,” that is, that meaning and truth emerge logically from results, that scientific discovery is an inductive process, that generalizations take shape from simple observations, and order comes out of disorder.

Medawar challenges Mill’s concept on three grounds:

  1. “There is no such thing as unprejudiced observation.” Every observation is biased, “a function of what we have seen or sensed in the past.”
  2. Formulation of the scientific idea and demonstration of proof are wholly different notions and activities.
  3. “It simply is not logically possible to arrive with certainty at any generalization containing more information that the sum of particular statements upon which that generalization was founded, out of which it was woven.”

Medawar maintains that neither Bertrand Russell nor Karl Popper had any use for induction, and suggests that: “. . . all scientific work of an experimental or exploratory character starts with some expectation about the outcome of the inquiry. This expectation one starts with, this hypothesis one formulates, provides the initiative and incentive for the inquiry and governs its actual form. It is in the light of this expectation that some observations are held relevant and others not; that some methods are chosen and others discarded; that some experiments are done rather than others. It is only in the light of this prior expectation that the activities the scientist reports in his scientific paper really have any meaning at all.” Thus, the formulation of hypotheses is an imaginative act, while testing the hypothesis “is a strictly logical and rigorous process based upon deductive arguments.”

In his strongest advice, however, is a caution: “…the intensity of the conviction that a hypothesis is true has no bearing on whether it is true or not. The importance of the strength of our conviction is only to provide a proportionately strong incentive to find out if the hypothesis will stand up to critical evaluation” (from: Advice to a Young Scientist, Medawar, 1970).

Thus, Yerushalmy and Hilleboe were right to criticize Keys’s particular method of testing his hypothesis. Keys was right, however, in testing his strongly believed hypothesis on diet-heart with data from all research modes. And his selection of countries for ecological analysis was based on personal knowledge of the reliability of those data. In the end, Keys conclusions pointed more clearly to the eventual causes of coronary death differences than had the statisticians’ use of all available countries’ data. (HB)

David Jacobs’ Thoughts:

  1. There is discovery and interpretation within any given dataset and data analysis, but I agree that the bias of the scientist is a very important factor in the interpretation and statements about discovery. Thus, I think that what belongs in the Introduction and what belongs in the Discussion of a paper needs very careful thought, and agree with Sir Peter on a substantial part of this point.
  2. No dataset is rich enough to contain information about all aspects of life. Whether trying to understand life or to make sensible policy, data are not enough; somewhere, however comprehensive the data, personal judgment and therefore personal responsibility comes in. (Peter Medawar)


Keys, Ancel. 1953. Atherosclerosis: a problem in newer public health. Journal of the Mount Sinai Hospital 20 (2):118-39.

Yerushalmy, J. and Hilleboe, H.H. 1957. Fat in the diet and mortality from heart disease. A methodological note. New York Medical Journal 57:2343-2354.