The rationality assumption grounds the ergodic axiom necessary to make economics appear similar to physics. However, this is just begging the question by assuming a priori what is needed to produce the desired result, which is anti-scientific. Samuelson's assumption of rationality is not much different from that of Mises in Human Action.
Karl Popper was willing to admit "the principle of rationality" as a heuristic device.
The 'principle of rationality' (or 'rationality principle') is coined by Karl R. Popper in his Harvard Lecture of 1963, published in his book Myth of Framework [1]. It is related with what he called the 'logic of the situation' in an Economica article of 1944/1945, published later in his book The Poverty of Historicism[2].There is a great difference between a heuristic device and a self-evident principle logically and methodologically. The first is used constructively in both science and engineering, while the latter is the basis of philosophical reasoning that begins with "first principles."
Following Popper the 'logic of the situation' is the result of reconstructing meticulously all circumstances if you are trying to understand a historical event. The 'principle of rationality' is the assumption that people try to reach their goals. Both the reconstruction of the 'logic of the situation' and the application of the 'principle of rationality' constitute an important method of understanding that seems to be useful in all social sciences. It is the method of creating theories due to our knowledge that men and women usually have goals and usually try to reach their goals. If this method is applied to a particular situation it results in a theory which can be proved as right or wrong. Although the 'principle of rationality' is not applicable to (natural) science there is no methodological difference between science and social sciences because both sciences are getting explanations by inventing theories which can be proved.
Popper called his 'principle of rationality' nearly empty (a technical term meaning without empirical content) and strictly speaking false, but nonetheless tremendously useful [3]. These remarks earned him a lot of criticism because seemingly he had swerved from his famous Logic of Scientific Discovery. — Wikipedia.
Economics departments — turning out generation after generation of idiot savants
Lars P. Syll | Professor, Malmo University
