2. _A definition that suggests clear and familiar thoughts to the student seem at first much more difficult to get in any social science than in the natural sciences._ These deal with concrete, material things which we are accustomed to see, handle, and measure. If a mere child is told that botany is a study in which he may learn about flowers, trees, and plants, the answer is fairly satisfying, for he at once thinks of many things of that kind. When, in like manner zoölogy is defined as the study of animals, or geology as the study of rocks and the earth, the words call up memories of many familiar objects. Even so difficult and foreign-looking a word as ichthyology seems to be made clear by the statement that it is the name of the study in which one learns about fish. It is true that there may be some misunderstanding as to the way in which these subjects are studied, for botany is not in the main to teach how to cultivate plants in the garden, nor ichthyology how to catch fish or to propagate them in a pond. But the main purpose of these studies is clear at the outset from these simple definitions. Indeed, as the study is pursued, and knowledge widens to take in the manifold and various forms of life, the boundaries of the special sciences become not more but less sharp and definite. [Sidenote: Economics studies some social acts and relations] Political economy, on the other hand, as one of the social sciences, which deal with men and their relations in society, seems to be a very much more complex thought to get hold of. We are tempted to say that it deals with less familiar things; but the truth may be, as a thoughtful friend suggests, that the simple social acts and relations are more familiar to our thought than are lions, palm-trees, or even horses. Every hour in the streets or stores, one may witness thousands of acts, such as bargains, labor, payments, that are the subject-matter of economic science. Their very familiarity may cause men to overlook their deeper meaning. Many other definitions have been given of political economy. It has been called the science of wealth, or the science of exchanges. Evidently there are various ways in which wealth may be considered or exchanges made. The particular aspects that are dealt with in political economy will be made clear by considering two other questions, the place of economics among the social sciences and the relation of economics to practical affairs. § II. PLACE OF ECONOMICS AMONG THE SOCIAL SCIENCES [Sidenote: Economics contrasted with the natural sciences]