It is important to point out at the outset that in the following pages the word ‘analogy’ is used in the sense of ‘analogical reasoning.’ The Oxford English Dictionary defines this sense of the word as: ‘The process of reasoning from parallel cases; presumptive reasoning based upon the assumption that if things have some similar attributes, their other attributes will be similar’.

The term ‘analogy’ has a number of other related usages: to make the point that a treaty is like a contract, it is sometimes said (1) that there is an ‘analogy’ between treaty and contract, or, exceptionally, and perhaps incorrectly, (2) that the ‘domestic analogy’ of treaty is contract. In (1), the word ‘analogy’ means ‘correspondence’, ‘affinity’ or ‘similarity’, and in (2) it really means an ‘analogue’, ‘counterpart’ or ‘comparable object’. This book, however, is concerned with ‘analogy’ only in the sense of ‘analogical reasoning.’ The term ‘analogy’ will be used in this sense alone throughout the following discussion except when it has been used otherwise in a passage to be quoted from other works.

The ‘domestic analogy’, then, may broadly be defined as presumptive reasoning (or a line of argument embodying such reasoning) about international relations based on the assumption that since domestic and international phenomena are similar in a number of respects, a given proposition which holds true domestically, but whose validity is as yet uncertain internationally, will also hold true internationally.