If we define utility as the capacity that goods and services possess for satisfying necessities, overcoming scarcity consists in short of increasing utility. The scale of values of items embraces influences the whole range of utilities, from the negative, to zero (they would be free goods), to positive values (real economic goods). The impossibility of a quantitative calculation of utility does not invalidate its use as an instrument of economic analysis, since the logic of citizens' actions can be derived from qualitative trials that do not need numeric precision. It is logical for this reason that one of the current keys for understanding economic processes is the study of the consumer's individual and family behaviour.

On the other hand, the return to the personal and micro-economic analysis is one of the most alluded to current trends in economic theory. People have become aware again that the economic process is not something that happens outside of us, by way of something objective and mechanical, but rather it is a process to which we all contribute with the essence of our deliberations and resolutions. What is hidden behind the phenomenon of economic life that appears objected in the price, quantity, money, interest or moment, are thousands and thousands of subjective processes produced deep down in each and every one of us. The importance, in short, of the micro-economy in general, and of the consumer's behaviour in particular is highlighted in this statement by Hicks in his book Value and Capital: "The first thing that it is necessary to do (in economy) is a study of the behaviour of the outstanding person and company." (...) that is supplemented and reinforced by the other: During this century the pure theory of consumer demand has been studied little, a subject to which Marshall and his contemporaries paid great attention."

Jevons, Walras, Menger and the whole Austrian school along with the precedents of Balmes and Gossen, give the appropriate solution to the problem of value through the doctrine of marginal, last or border utility as Menger called it.

All the economic manuals echo the law of falling marginal utility according to which the quantity of additional or marginal utility diminishes as a person consumes a greater quantity of a good. Total utility tends to increase as we consume a greater quantity of a good. However, as we consume more, our total utility increases in a lower and lower dose.

Using this fundamental rule of consumer behaviour based on the law of falling marginal utility an attempt is made to explain the negative slope of the demand curves. The rise in price of a good reduces its optimum consumption, which indicates that the demand curves have a negative slope. Increasing the price decreases the demanded quantity and vice versa: dropping the price increases demand.

But the law of falling marginal utility has some restrictive hypotheses and their fulfilment distances it from the daily reality in our cultural society of reflection and knowledge. These restrictions can be summarized saying that this theory: 1) has a professedly static character, 2) needs to consider the different units of the considered merchandise exactly the same and homogeneous, 3) implies independent utilities between the different goods and 4) it considers the scale of the consumer's preferences as constant. It is difficult for these four conditions to occur in our real decisions: The time and place make each decision completely original; the tendency is to produce goods key in hand and with different units between them, adapted to each potential client's original preferences. The utilities of different goods are highly interdependent on each other and, of course, the scale of preferences changes continually.

The movement of the classic industrial society to the post-industrial society is characterized by globalisation and growing interdependence. In just a few years the social structures that tried to operate in tight compartments have changed to a model in which inter-communication penetrates everything. Now "everything has to do with everything." Society has been made much more complex. If we continue anchored in former static paradigms, this growing interdependence will be misunderstood.

It is necessary to consider that dynamisation as a challenge for the intelligence and an amplification of the field of exercise of human freedom. It is necessary to abandon inertial postures and have innovative attitudes in the productions of goods and services, because there are innovative attitudes in the demand for products and services on the part of the consumers. More and more economists allege with Shackle that the typical economic decision has elements of singularity, or of no-comparability with previous decisions.

From preferably analytic and functional focuses, we pass to synthetic and understanding visions. Man in society, natural protagonist of economic activity, emerges with his unitary reality and tries to collect a group of goods and services more and more harmonic with that unitary reality. Each individual or family demands in each moment what they consider more useful for building their combined and unitary project of life and these demands depend fundamentally upon what has been already possessed and consumed previously of a complementary character and upon its always original personal aptitudes.

If all these appreciations come closer to reality it is necessary to speak of a growing complementary marginal utility that will be present in the economic agents' numerous decisions. Falling marginal utility was one of the foundations of the negative slope of the curve of singular demand. As the price diminishes, the demanded quantity increases and, in turn, as the demanded quantity increases one is willing to pay an inferior price for the last units, since the marginal utility is less.

If we consider goods or services with growing complementary marginal utilities, in some or all of their sections, it would be convenient to distinguish among: 1) functions of demand where the dependent variable is the demanded quantity and the independent one the price that it is necessary to pay to obtain each unit, and 2) the functions of demand, in the way that Marshall defined them, where the dependent variable is the price that the consumer is willing to pay for the acquisition of a new unit of the good in question. For the functions of demand of the first type, the growing marginal utility does not have repercussions on the negative slope of these curves: If the price that it is necessary to pay decreases, the demanded quantity increases and if the price increases then the quantity diminishes. But in Marshall's demand curves, for the acquisition of new units of these goods and services the consumer would be willing to pay a higher price since the marginal utility would be rising.

In a post-industrial society, where human capital and the tertiary sector have a more and more dominant role, it is advisable to study the consequences that the existence of goods and services with very elastic and even growing complementary marginal utilities have for personal, family and social economic development. Thousands of manuals of Economic Theory are becoming obsolete for interpreting and understanding economic phenomenon in the society that we have been seeing appear for years.

Joseph John Franch Menéu
Professor of Political Economy
Autonomous university of Madrid
Gaceta de los Negocios