Like the idealist, the realist stresses a curriculum consisting of organized, separate subject matter, content, and knowledge that classifies objects. For example, the experiences of humankind comprise history. Animals can be studied as zoology. Like the idealist, the realist locates the most general and abstract subjects at the top of the curricular hierarchy and gives particular and transitory subjects a lower order of priority. Logic and lessons that exercise the mind and that cultivate rational thought are stressed. Concepts and systems that can be organized into subjects—such as ethical, political, and economic thought--are also included in the curriculum. The three Rs (reading, writing, and arithmetic) are also necessary in a person's basic education.