Political theory is not political philosophy, which is a distinct discipline. Political theory is the explanation of the nature and function of the State or political system, derived from data or descriptive analysis, with a view to understand it. It implies prediction of what it will be in future.
Theory is, therefore, strictly an empirical thought. Of course, political rigor has varied from age to age and from time to time. In the past ages, it was influenced by religion, dogma and ideology.
In the nineteenth and early twentieth century’s, it was influenced by the institutional or static approach towards political life. Accordingly, it dealt with such concepts as State, government, justice, liberty.