1. _Political economy, as one of the social sciences, may be contrasted with the natural sciences, which deal with material things and their mutual relations, while it deals with one aspect of men's life in society, namely, the earning of a living, or the use of wealth._ It is true that political economy also has to do with plants and animals and the earth--in fact, with all of those things which are the subject-matter of the natural sciences; but it has to do with them only in so far as they are related to man's welfare and affect his estimate of the value of things; only in so far as they are related to the one central subject of economic interest, the earning of a living. [Sidenote: Character of the social sciences] 2. _The social sciences deal with men and their relations with each other._ The word "social" comes from the Latin socius, meaning a fellow, comrade, companion, associate. As men living together have to do with each other in a great many different ways, and enter into a great many different relations, there arise a great many different social problems. Each of the social sciences attempts to study man in some one important aspect--that is, to view these relations from some one standpoint. Man's acts, his life, and his motives are so complex that it is not surprising that there has been less definiteness in the thought of the social sciences, and that they have advanced less rapidly toward exactness in their conclusions, than have the natural sciences. This complexity also explains the discouragement of the beginner in the early lessons in this subject. Usually the greatest difficulties appear in the first few weeks of its study. The thought is more abstract than in natural science; it requires a different, I will not say higher, kind of ability than does mathematics. But little by little the strangeness of the language and ideas disappears; the bare definitions become clothed with the facts of observation and recalled experiences; and soon the "economic" acts and relations of men in society come to be as real and as interesting to the student as are the materials in the natural world about him--often, indeed, more interesting. [Sidenote: Economics, politics, law, and ethics]