Philosophy and economics, also philosophy of economics, consists of inquiries concerning rational choice, the appraisal of economic outcomes, institutions and processes, and the ontology of economic phenomena and the possibilities of acquiring knowledge of them. Although these inquiries overlap in many ways, it is useful to divide philosophy of economics in this way into three subject matters which can be regarded respectively as branches of action theory, ethics (or normative social and political philosophy), and philosophy of science. Economic theories of rationality, welfare, and social choice defend substantive philosophical theses often informed by relevant philosophical literature and of evident interest to those interested in action theory, philosophical psychology, and social and political philosophy. Economics is of particular interest to those interested in epistemology and philosophy of science both because of its detailed peculiarities and because it possesses many of the overt features of the natural sciences, while its object consists of social phenomena.
The question usually addressed in any subfield of philosophy (the philosophy of X) is "what is X?" A philosophical approach to the question "what is economics?" is less likely to produce an answer than it is to produce a survey of the definitional and territorial difficulties and controversies. Similar considerations apply as a prologue to further discussion of methodology in a subject. Definitions of economics have varied over time from the modern origins of the subject, reflecting programmatic concerns and distinctions of expositors.
Ontological questions continue with further "what is..." questions addressed at fundamental economic phenomena, such as "what is (economic) value?" or "what is a market?". While it is possible to respond to such questions with real verbal definitions, the philosophical value of posing such questions actually aims at shifting entire perspectives as to the nature of the foundations of economics. In the rare cases that attempts at ontological shifts gain wide acceptance, their ripple effects can spread throughout the entire field of economics.