Although physical scientists sometimes appear unwilling to recognise the greater complexity of the problems of human interaction, the fact itself was seen more than a hundred years ago by no less a figure than James Clerk Maxwell, who in 1877 wrote that the term `physical science' is often applied `in a more or less restricted manner to those branches of science in which the phenomena considered are of the simplest and most abstract kind, excluding the consideration of the more complex phenomena such as those observed in living things'. And more recently a Nobel laureate in physics, Louis W. Alvarez, stressed that `actually physics is the simplest of all the sciences But in the case of an infinitely more complicated system, such as the population of a developing country like India, no one can yet decide how best to change the existing conditions' (Alvarez, 1968). Mechanical methods and models of simple causal explanation are increasingly inapplicable as we advance to such complex phenomena. In particular, the crucial phenomena determining the formation of many highly complex structures of human interaction, i.e., economic values or prices, cannot be interpreted by simple causal or 'nomothetic' theories, but require explanation in terms of the joint effects of a larger number of distinct elements than we can ever hope individually to observe or manipulate. It was only the `marginal revolution' of the 1870s that produced a satisfactory explanation of the market processes that Adam Smith had long before described with his metaphor of the `invisible hand', an account which, despite its still metaphorical and incomplete character, was the first scientific description of such self-ordering processes. James and John Stuart Mill, by contrast, were unable to conceive of the determination of market values in any manner other than causal determination by a few preceding events, and this inability barred them, as it does many modern 'physicalists', from understanding selfsteering market processes. An understanding of the truths underlying marginal utility theory was further delayed by James Mill's guiding influence on David Ricardo, as well as by Karl Marx's own work. Attempts to achieve mono-causal explanations in such areas (prolonged