Foreign policy rests on an interpretation of observed facts and events. These interpretations are never given in the sense of being contained in the events. They are assumptions or hypotheses which are used to relate the events in some sort of causal order, that enables us to understand them, as we say, and to make predictions about what is likely to happen. Policy then consists in the formation of purposive action to influence the causal order of events and to protect, as far as possible, the interests of one's own country in the expected contingencies. Discussions of foreign policy in Canada, both in the press and, sometimes, in official circles, have too frequently not been based on sound assumptions. There is a tendency to believe that invective and violent denunciation are acceptable substitutes for calm, scientific thinking. Indeed there is a fundamental misunderstanding of the nature of scientific methods of thought. The leaders of the Soviet Union possess a system of working assumptions, derived a priori from the Marxist philosophy. They believe that Western capitalism is doomed to further crises and depressions, that these will seriously disturb the whole social framework with revolutionary and counter-revolutionary forces, and that, before the leaders of Western capitalism accept social elimination, they will plunge the world into a counterrevolutionary war. The Soviet Union, they believe, will be the principal object of aggression in such a war. The utterances of certain irresponsible members of the United States Congress, of certain business leaders, and the hysterical maledictions of a large section of the American press are taken as empirical evidence supporting the basic Marxist doctrine. The leaders of the Soviet Union, therefore, have the responsibility of putting Russia, the base of world communism, in the strongest possible attitude of defence. The classic invasion routes must be secured,