Theory: (Webster) a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena; a body of theorems presenting a concise systematic view of a subject; the general or abstract principles of a body of fact, a science, or an art.

Prescriptive or normative theory:  theory that rests upon ethical commitments and things or behaviors to be prized, preferred, and valued.

Descriptive theory: a theory which attempts to explain what is rather than what ought to be.

Empirical Theory:  theory which is testable utilizing the procedures of the scientific method.


Lawrence J. R. Herson, The Politics of Ideas, 1984

 "All in all, normative theory is the essence of political debate. We use it to plead our cause and to convince others to join us in that cause. Both theories devote themselves to identifying and defining relationships between logical classes, between means and ends, or cause and effect. Every normative theory contains descriptions, and convincing normative theory generally contains elaborate descriptions of real world conditions...Conversely, a theory ordinarily classed as descriptive generally contains (or implies) normative elements, including a premise to this effect: If we describe things as they are, we are then likely to agree on changes that will reconstruct things as they ought to be. All in all, most theories important to the politics of ideas are both descriptive and prescriptive".