Before setting out on these inquiries, I ought perhaps to state explicitly what I intend to mean by development. This is a term which quite obviously is capable of a variety of meanings. In regard to economic systems it might mean increase in the absolute size of, for instance, capital or annual production regardless of the size of the population – the sense in which it was commonly used before the rise of classical economics and in which it is sometimes used in popular discussion today. It might mean increase in complexity, in the articulation of various different functions. It might mean progress towards some’ethically defined goal. But I shall not use this term in any of these senses. The sense in which I shall use it throughout will be the sense in which it is used nowadays in the various comparative tables to which we have recourse when we discuss degrees of development, and the sense in which, since the days of Adam Smith’s The Wealth of Nations, it has been used in the so-called theory of production.

That is to say, I shall use it in relation to movements in real income per head and to potential in this respect – real income being conceived as a stream of availability of goods and services as distinct from the experiences or satisfactions to which it gives rise. In doing this, I am not at all unaware of the very considerable conceptual difficulties involved in measurements of this kind; if need be I could at once elaborate a whole series ofmethodological scruples and reservations. But my main business here is to give an account of an evolution of thought; and at this stage I think that we can defer considerations of this sort and proceed with the good sense of the historical. perspective. If we take the term development in this sense, it is surprising what a considerable extent of the economic thought of the past can be brought into the picture.

Needless to say, it would be absurd to claim that the whole corpus can be so classified. Thefundamental theories of structural relationships, the theories ofvalue and distribution, for instance, can be studied, as in modern equilibrium analysis, quite independently of the idea of development. Yet if we realise that development conceived algebraically – i.e. with either a plus or a minus sign, is more or less the same as change on an aggregate or near-aggregate scale, and if we realise the underlying normative urge of much of the speculation of the past, it is not difficult to see what a l~rge part of the field may be regarded as relevant. The search for causes of improvement of production per head informs a great deal of the literature of the subject.