The applied study of philosophy yields applications such as those in ethics—applied ethics in particular—and political philosophy. The political and economic philosophies of Confucius, Sun Zi, Chanakya, Ibn Khaldun, Ibn Rushd, Ibn Taimiyyah, Niccolò Machiavelli, Gottfried Wilhelm Leibniz, John Locke, Jean-Jacques Rousseau, Adam Smith, Karl Marx, John Stuart Mill, Leo Tolstoy, Mahatma Gandhi, Martin Luther King Jr., and others—all of these have been used to shape and justify governments and their actions.
In the field of philosophy of education, progressive education as championed by John Dewey has had a profound impact on educational practices in the United States in the 20th century. Descendants of this movement include the current efforts in philosophy for children, which are part of philosophy education. Carl von Clausewitz's political philosophy of war has had a profound effect on statecraft, international politics, and military strategy in the 20th century, especially in the years around World War II. Logic has become crucially important in mathematics, linguistics, psychology, computer science, and computer engineering.
Other important applications can be found in epistemology, which aid in understanding the requisites for knowledge, sound evidence, and justified belief (important in law, economics, decision theory, and a number of other disciplines). The philosophy of science discusses the underpinnings of the scientific method and has affected the nature of scientific investigation and argumentation. As such, philosophy has fundamental implications for science as a whole. For example, the strictly empirical approach of Skinner's behaviorism affected for decades the approach of the American psychological establishment. Deep ecology and animal rights examine the moral situation of humans as occupants of a world that has non-human occupants to consider also. Aesthetics can help to interpret discussions of music, literature, the plastic arts, and the whole artistic dimension of life. In general, the various philosophies strive to provide practical activities with a deeper understanding of the theoretical or conceptual underpinnings of their fields.