… is from page 10 of W. Duncan Reekie’s splendid 1979 volume, Industry, Prices and Markets:
In summary, the competitive process provides incentives and so evokes effort. It generates a continuous and universal search for substitutes, for ways of replacing the less desirable by the more desirable. This process of substitution begins with the consumer seeking to distribute his income to the best advantage and passes on to the producer striving to replace the less by the more sought-after goods and substituting a better way of producing for a worse way. The essence of the process is choice by the consumer; emulation, rivalry and substitution by the producer.