Science Heresy - October 2010

Sir Karl Popper

What is the Scientific Method?

Popper's Principles

The scientific method was set out by Sir Francis Bacon in the early 17th century and was further refined by Newton and others culminating in the ideas of Popper. His seven principles are worth restating in full (Popper,1963), viz.:

  1. It is easy to obtain confirmations, or verifications, for nearly every theory — if we look for confirmations.
  2. Confirmations should count only if they are the result of risky predictions; that is to say, if, unenlightened by the theory in question, we should have expected an event which was incompatible with the theory — an event which would have refuted the theory.
  3. Every "good" scientific theory is a prohibition: it forbids certain things to happen. The more a theory forbids, the better it is.
  4. A theory which is not refutable by any conceivable event is non-scientific. Irrefutability is not a virtue of a theory (as people often think) but a vice.
  5. Every genuine test of a theory is an attempt to falsify it, or to refute it. Testability is falsifiability; but there are degrees of testability: some theories are more testable, more exposed to refutation, than others; they take, as it were, greater risks.
  6. Confirming evidence should not count except when it is the result of a genuine test of the theory; and this means that it can be presented as a serious but unsuccessful attempt to falsify the theory.
  7. Some genuinely testable theories, when found to be false, are still upheld by their admirers — for example by introducing ad hoc some auxiliary assumption, or by reinterpreting the theory ad hoc in such a way that it escapes refutation. Such a procedure is always possible, but it rescues the theory from refutation only at the price of destroying, or at least lowering, its scientific status.

Most working scientists would recognize these ideas and would support their application in their own research field.

Popper’s principles are well served by methods of statistical inference developed by Fisher (1925) and others in the early part of the 20th century. These methods formalize and quantify the idea of falsifiability by introducing the concept of the “Null Hypothesis”, that is, a hypothesis which has been set up to be deliberately falsified using the methods of mathematical statistics. The Null Hypothesis usually takes the form of an assumption that a sample comes from a population with a known distribution or that two or more samples come from the same population. This technique is known as “hypothesis testing”.

The remarkable advances in science and technology witnessed in the modern era are largely the result of the meticulous application of these two complementary approaches. When a model is hypothesis tested and fails the test, new insights into the underlying science are frequently gained, whereas clinging tenaciously to “correct” theories leads only to a sterile absolutism. This is the fundamental difference between science and superstition.

Many fields of physical science have come to be dominated by people whose backgrounds lie in Applied Mathematics and who are frequently ignorant of the scientific method as outlined above. To many applied mathematicians, the internal consistency of the mathematical formulation of a physical problem is all that matters. Rigorous observational testing of models is not seen as relevant. This is particularly true of environmental sciences such as oceanography and climatology. Only in biological fields has the need for rigorous testing continued to be recognised. Perhaps this accounts for the ongoing successes of the biological sciences. In contrast the physical sciences have languished in recent times and resorted to political methods to restore their flagging fortunes.


Fisher, R. A. (1925), Statistical Methods for Research Workers, Oliver and Boyd, Edinburgh.

Popper, K. (1963), Conjectures and Refutations, Routledge and Keagan Paul, London.

Author's Note

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October 2010