This has been a recurring question in the history of economics and of economic thought. If we start from that the science is based on the application of the reason in the search of knowledge and that we want to know how it is developed, which are the constraints it has, which is the difference between scientific knowledge and other types of knowledge, to what extent are comparable the hard sciences -Physics, Chemistry- with other disciplines that, in a way perhaps abusive, have also been called sciences: the humanities and social sciences.
This is the theme that has always worried us: if economics is a science, especially in comparison to the sciences that have been called hard sciences. John K. Galbraith answered it forcefully in 1977: "the economy is not an exact science." In the nineteenth century, in front of the pessimism of Malthus, Carlyle spoke of economics as the dismal science, an expression that has been used often from then. Among the classical economists, Marx concluded that any economic or social theory was influenced by the ideology and values of those who proposed it. Later, Weber insisted in that: if people studying economics and society wanted to be scientific, they had to set aside the judgments of value and the ideology.
Keynes in a letter to Harrod (1938) had said that "economics is essentially a moral science and not a natural science. That is to say, it employs introspection and judgments of value." What's more, "economics is a science of thinking in terms of models joined to the art of choosing models which are relevant to the contemporary world. It is compelled to be this, because, unlike the typical natural science, the material to which it is applied is, in too many aspects, not homogeneous through time". Also Schumpeter in 1948 had entitled "Science and ideology" his speech at the annual meeting of the American Economic Association, where even showing his relative optimism about the ability of economists to use scientific advances for leaving aside ideological biases, he concluded that all this "still leaves us with the result that some ideology will always be with us and so, I feel convinced, it will".
For Joan Robinson, who has left us a book - "Economic Philosophy" (1962) - on the subject, "... economics itself ... has always been partly a vehicle for the ruling ideology of each period as well as partly a method of scientific investigation". She notes that, although perhaps it is different in what she calls the "respectable sciences", in the investigations of psychological and social problems, metaphysics plays an important role. However, for Robinson, whether or not it can be removed from the knowledge in the social sciences, ideology is indispensable in the action in social life. Any economic system requires a set of rules, an ideology that justifies these rules, and an awareness and effort of individuals to achieve them and make them real. But "the great difficulty of social sciences (if you may presume to call them so) of applying scientific method, is that we have not yet established an agreed standard for the disproof of an hypothesis. Without the possibility of controlled experiment, we have to rely on interpretation of the evidence, and interpretation involves judgment; we can never get a knock-down answer. But because the subject is necessarily soaked in moral feelings, judgement is coloured by prejudice".
Economic variables are different from the ones in the "hard sciences" for several reasons: a very high number of complex variables to be analysed; it is difficult to identify, isolate and measure many of these variables often interrelated in a complicated way; the historical dimension of the facts, which makes that the variables studied are not permanent and repeatable as in the natural sciences, makes the verification of theories very difficult and produces certain cumulative processes; the human component of variables can lead to inconsistent and unpredictable elections; the difficulties of making predictions reasonably accurate has made to say that "the only function of economic forecasting is to make astrology look respectable" attributed to Galbraith but that it seems it was already used before by Ezra Solomon.