Since man, when he migrates, leaves a fixed home in response to a rational impulse, there must be some definable cause for the migration. There are certain general causes which are found to underlie all migratory movements, and which are worthy of examination. In the first place we find that the cause of a migratory movement must be a powerful one. Man inevitably becomes attached to the locality in which he finds himself placed. Bonds of many kinds arise to tie him to his home. Among these may be mentioned family connections, sentimental associations, familiar customs and habits of the community, political and religious attachments, business interests, property owned, superstitious veneration for graves. All of these, and others, unite to make the home ties very strong. The life of man is closely bound up with his environment, and a change of environment is a momentous event. As a result, there is a marked inertia, a resistance to pressure, among human beings, and the presumption is that people will stay where they are, unless some positive force causes them to move. And no trivial occasion will suffice. This force, which results in movement, may be a very complex one, but in general it must present one of two aspects—it must be either attractive or repellent. Men are either drawn or driven to break the ties which bind them to their native locality. The attractive force must, of course, exist in the country which is the objective point, the repellent force, in the existing environment. This distinction is well brought out by Professor Otis T. Mason, who classifies the causes of migration into “positive”—advantages, satisfactions, etc.—and “negative”—discomforts, compulsions, etc.[2] In view of the strength of the “home ties,” however, it is evident that the repellent type of forces must be much the more important. It would have to be a very alluring prospect indeed that would lead a man to leave a spot where he was contented. In fact we can hardly conceive of a man deserting a spot where he was really contented. There must be some dissatisfaction with existing conditions to induce him to take the step. Attractions often operate by inducing dissatisfactions, through comparison. There is no attraction in a foreign region unless it seems superior to the home surroundings. Then the home conditions appear inferior, and there is dissatisfaction. This is what Professor Sumner called a process of idealization.