Basic concepts in political science have been used in a purely classificatory way ever since Aristotle established the sixfold classification of the forms of government: monarchy, aristocracy, constitutional government, and their respective “perversions”: tyranny, oligarchy, democracy. Similarly, a modern writer distinguishes among four types of political systems: the Anglo-American, the Continental European, the pre-industrial (or partially industrial), and the totalitarian. All these are categorical concepts; a political system is either monarchical or not, either of the Anglo-American or of another type. Such key terms as influence, control, authority, power, and freedom also tend to function categorically: one actor either has or lacks power over some activity of another actor; with respect to one actor, another is either free or unfree to act in a certain way.However, concrete political situations exhibit such characteristics to different degrees. Just as the substances we encounter in nature have varying degrees of hardness (rather than being either hard or soft), so a given political system is more, or less, totalitarian (or of the Anglo-American or of the pre-industrial type) than another. The United States and Soviet Russia have at present more power than any other country, and both are perhaps about equally powerful. Soldiers in general have less freedom than civilians, but they have more than prisoners. There can (or there cannot) be equal freedom for all.Since we do make such assertions, the question arises whether it is possible to give them precise empirical meaning. To do so, we must replace such categorical concepts as power and freedom by the corresponding comparative concepts, e.g., “more power than,” “as much freedom as,” and provide operational definitions for these expressions.