Popular understandings of economics often attempt to incorporate the methodology of natural sciences as the supposed key to economics. Some economic experts are of the view that the methods employed by the natural sciences, such as advanced mathematics, are important tools for the assessments of historical data to establish the state of an economy. It is also believed that the knowledge secured from the assessment of the empirical data is likely to be tentative since it is not possible to know the true nature of reality. Thinkers such as Milton Friedman held that the best approach to comprehend this elusive reality is to build a model that could generate accurate forecasts.

For instance, an economist forms a view that consumer outlays on goods and services are determined by disposable income and interest rates. Based on this view, he formulates a model, which is then validated by means of quantitative methods. An important test of the model is how well it fits with empirical data. The better the fit with the historical data, the higher the likelihood that the model is likely to be accepted as a useful tool for the assessment of the future consumer outlays.

In order to secure a good predictive model, what matters here is how well consumer outlays are correlated with disposable income and interest rates. If the model fails to produce accurate forecasts, it is either replaced, or modified by adding some other explanatory variables. By following such thinking, the economist forms a view of the world of economics by means of the model's forecasting accuracy. If the model generates accurate forecasts, then it could mean that the model closely resembles the real world. However, what about a situation where the model does not generate accurate forecasts yet its structure seems to be well-designed? Or, how do we treat models of different structures that generate accurate forecasts?

To make sense of the data, one must necessarily have a theory; one which stands on its "own feet," and did not originate from the data. The heart of such a theory is that it must originate from something logically consistent, informs about the nature of reality, and cannot be refuted. A theory that rests on the foundation that human beings are consciously and purposefully employing means to reach goals -- human action -- conforms with this requirement.

"This methodology [empiricism], briefly, is to look at facts, then frame ever more general hypotheses to account for the facts, and then to test these hypotheses by experimentally verifying other deductions made from them. But this method is appropriate only in the physical sciences, where we begin by knowing external sense data and then proceed to our task of trying to find, as closely as we can, the causal laws of behavior of the entities we perceive. We have no way of knowing these laws directly; but fortunately, we may verify them by performing controlled laboratory experiments to test propositions deduced from them. In these experiments we can vary one factor, while keeping all other relevant factors constant ... there is greater possibility that some other explanation will be devised which fits more of the observed facts and which may then replace the older theory."

"The mathematical method must be rejected not only on account of its barrenness. It is an entirely vicious method, starting from false assumptions and leading to fallacious inferences. Its syllogisms are not only sterile; they divert the mind from the study of the real problems and distort the relations between the various phenomena."

"Not only measurement but the use of mathematics in general in the social sciences and philosophy today, is an illegitimate transfer from physics. In the first place, a mathematical equation implies the existence of quantities that can be equated, which in turn implies a unit of measurement for these quantities. Second, mathematical relations are functional; that is, variables are interdependent, and identifying the causal variable depends on which is held as given and which is changed. This methodology is appropriate in physics, where entities do not themselves provide the causes for their actions, but instead are determined by discoverable quantitative laws of their nature and the nature of the interacting entities. But in human action, the free-will choice of the human consciousness is the cause, and this cause generates certain effects. The mathematical concept of an interdetermining 'function' is therefore inappropriate.

From this it follows that the present consumer goods are at a premium to the identical basket of future consumer goods. The premium is the interest. Hence, interest rates cannot be negative. If, however, we do observe negative interest rates, this does not falsify the theory, but rather forces the analyst to figure out how this could have happened and what other variables might have been in play. Most likely he will discover that the main reason for the discrepancy between the observed data and the theory is on account of central bank monetary policies, which have distorted the market interest rates. Again, no quantitative methods are required to validate a logically-ascertained theory.