What is a Substitute?
(Based on Robbins, L. (2007). An essay on the nature and significance of economic science.)
Is an apple a substitute of an orange, or of a full meal? Or can an orange be substituted for water, or its peal for the colour of a drawing?
How something becomes a substitute? Whereas economics takes the data about means and ends as given, it is not really indifferent about how apparently given means, which are initially not considered as substitutes, become substitutable.
One may say that the discovery of something as a substitute of another is the result of lateral, and/or abstract thinking. And since these tasks are costlier, i.e. consume our scarce time, and attention which has alternative uses, it is now an economic issue. Given a set of means and ends, an agent may choose to engage in expending their cognitive resources, and time, in order to discover how the given set of means may be combined and used in the stead of an unavailable resource, or of a costlier one when cost reduction is the most desired. This task of discovering a substitute now becomes relatively more valued than buying costlier resource.
Since goods do not have any inherent value, it follows also that goods are not inherently substitutes. They are transformed into substitutes depending on some conditions in the same way different uses of the same good exist for different people depending on their unique conditions. However, in preceding reasoning it is clear that there exists a possible scenario where substitutability has an economic rationale, it is subject to conditions of scarcity of means and nature of our ends. For an instance, if using premium software is costlier, and we wish to avoid increased costs, we may find a combination of several freeware which provide us with the similar results, provided we have the creativity to obtain such results indirectly, which costs us time.
However, what really are those conditions under which engaging in lateral, abstract thinking becomes relatively more valued for discovering a substitute? This is a question that may require some import of knowledge from the science of psychology. This then can provide an economic rationale for creativity in general, and definition of substitute more deeply rooted in economic reasoning than merely as the positive cross price elasticity of demand of a good after extracting income effects.
Hence, it appears that we may be able to define substitute as a function of means and ends, at least for some conditions, and those conditions, their further survey, their nature, and consequences, and their importance in various businesses of life, these are few of the areas worth exploring in an interdisciplinary manner because studies in abstract and creative thinking have been carried out mostly by psychologists. By a combination of their findings regarding profile of agents, pressure, and other environmental settings, with our tools of mathematical analysis, we can derive a mathematical model of creativity in general, and a better definition of substitute in particular.