Here is one specific example, and then I will provide a discussion about applications and kinds of philosophical theories.

Marxism is an economic and historical philosophy. Common phrases to describe this philosophy are "historical materialism" and "dialectical materialism." Marx (and Engels) believed that culture arose from historical and economic factors. Even literature, science, and the arts emerged from these factors. Marxism was/is a critique of capitalism and a prognosis for the future.

Marxism is a theory of how humanity functions and reproduces (keeps functioning). Those who were/are Marxists have a philosophical theory about the world that is derived from these ideas. Some might favor a socialist society for a country or the world. Some might focus on economic and historical factors and how these control culture and ways of thinking. Marx gave a lot of thought to ideology and how it emerged from historical conditions. To have a Marxist philosophy or theory of the world, one would have to look at how economics and history determine who we are, how we work, and what we think.

Using a Marxist theory, it could also be said that a person sees the world through a Marxist "lens." Likewise, one might see the world through the lenses of other political or philosophical theories: feminism, socialism, capitalism, rationalism, idealism, and so on. These theories are not just ways of describing the world. They can be used to change the way we see the world or enact programs for changing the way the world is.

There are a number of ways to think about what a philosophical theory is. The Marxist example can fit most or all of these uses. A philosophical theory is a description of the world. Alternatively, it can be understood as a description of how we perceive the world (rationalism and idealism are broad examples here).

The word “theory” can be defined as “a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained.” A more general definition is an explanation of the interaction between facts, observations, and principles. In other words, a theory is how a set of points is described. The theory of relativity, for example, provides a meaningful explanation about the distribution of mass and its effect on space-time. A language’s grammar, which collects observations or prescriptions on how morphemes can be combined and arranged, could be considered the theory of that language. Philosophical theory, specifically, is more of a collection of beliefs or statements that describe a particular philosophy.

Political Theory

Political theory asks questions about the purpose, structure, necessity, and components of government. It is concerned with the state, politics, justice, and law. Rather than focus on how an individual should act, political theory focuses on how societies should be established and how individuals should act within the context of that society. It wants to know which rights are granted to members of a society and how a government should be set up to protect and ensure these rights.

Ethical Theory

Ethical theory asks questions about right and wrong. It is concerned with how people act, what they think is right, why they think it is right, and how these ethical notions can be put into action. Ethics is the theory of morality. It explains what moral actions are and attempts to define right conduct. It also tries to explain how that can lead to a satisfying, worthwhile life.

Metaphysical Theory

Metaphysical theory asks questions about reality and its nature. It wants to know why things exist, what existence is, and how things came into existence. According to Aristotle, metaphysics is the “first philosophy.” He divided metaphysics into three categories:

• Ontology – the study of being and existence
• Natural theology – the study of the divine
• Universal science – the study of first principles, logic, and reasoning

Analytic philosopher Charles Gelso defines a theory as: "a statement of the suspected relationship between and among variables." This definition as to what constitutes a theory is widely accepted in disciples such as economics, political science, the philosophy of natural science, and the philosophy of mathematics. A more sociological view is offered by philosopher James Heinen. In his view, theory comprises "a group of logically organized laws and relationships that continue explanation [within a given discipline]." This notion of what constitutes a theory emphasizes the socially constructed, historically contingent nature of theory itself.

Finally, the disciplines of linguistics and linguistic philosophy offer a third definition of theory. Theory, in these disciplines, can be understood as a set of language and linguistic rules aimed at answering fundamental questions such as who, what, where, when, and why. In this view, theory is understood as a particular type of expression and language use.