The Logic of Analogy

Abstract

How should a scientist argue when the data are insufficient to allow him to reason by classical or statistical models? After all, in most real world situations - in business or in war - that is the unhappy norm. In such cases the ordinary man instinctively argues by analogy, as Leibniz long ago showed; indeed if time presses, there is no alternative. The trouble, however, is that if we then include such arguments in our scientific reasoning, then, as we all know, this can lead to false conclusions. To escape from this dilemma, is there any alternative logical basis from which we can start our reasoning? What is proposed here is that instead of the well tried three valued logic of true, false or probable, we should adopt the three valued logic of true, false or possible. A rational system for analogue arguments can then be developed by these means, and with it the advantages brought by the use of symbols and so on. Such a method, however, includes many necessary changes as to how to structure our problems and how to apply new criteria; and it is some of these changes that are outlined in this note. For instance, it outlines the meaning of ‘causal relationships’ in analogue arguments, as well as how to define ‘rational choice’ in terms of analogue propositions. The advantage throughout is that this allows us to argue with less rather than more data.