structural:scholar_edition
Methodology

Metaphysicians employ a variety of methods to arrive at metaphysical theories and formulate arguments for and against them. Traditionally, a priori methods are the dominant approach. They rely on rational intuition and abstract reasoning from general principles rather than sensory experience. A posteriori approaches, by contrast, ground metaphysical theories in empirical observations and scientific theories. Some metaphysicians use perspectives from fields such as physics, psychology, linguistics, and history to conduct their inquiry. The two approaches are not exclusive and it is possible to combine elements from both. Which method a metaphysician employs often depends on their conception of the nature of metaphysics, for example, whether they see it as an inquiry into the mind-independent structure of reality, as metaphysical realists claim, or the principles underlying thought and experience, as some metaphysical anti-realists contend.

A priori approaches often rely on intuitions, that is, non-inferential impressions about the correctness of specific claims or general principles. For example, arguments for the A-theory of time, which states that time flows from the past through the present and into the future, often rely on pre-theoretical intuitions associated with the sense of the passage of time. Some approaches use intuitions to establish a small set of self-evident fundamental principles, known as axioms, and employ deductive reasoning to build complex metaphysical systems by drawing conclusions from these axioms. Intuition-based approaches can be combined with thought experiments, which help evoke and clarify intuitions by linking them to imagined situations while using counterfactual thinking to assess the possible consequences of these situations. To explore the relation between matter and consciousness, some theorists compare humans to philosophical zombies, that is, hypothetical creatures identical to humans but without conscious experience. A related method relies on commonly accepted beliefs instead of intuitions to formulate arguments and theories. The common-sense approach is often used to criticize metaphysical theories that deviate a lot from how the average person thinks about an issue. For example, common-sense philosophers have argued that mereological nihilism is false since it implies that commonly accepted things, like tables, do not exist.

Conceptual analysis, a method particularly prominent in analytic philosophy, aims to decompose metaphysical concepts into component parts to clarify their meaning and identify essential relations. In phenomenology, the method of eidetic variation is used to investigate essential structures underlying phenomena. To study the essential features of any kind of object, it proceeds by imagining this object and varying its features to identify which ones are essential and cannot be changed. The transcendental method is a further approach and examines the metaphysical structure of reality by observing what entities there are and studying the conditions of possibility without which these entities could not exist.

Some approaches give less importance to a priori reasoning and see metaphysics instead as a practice continuous with the empirical sciences that generalizes their insights while making their underlying assumptions explicit. This approach is known as naturalized metaphysics and is closely associated with the work of Willard Van Orman Quine. He relies on the idea that true sentences from the sciences and other fields have ontological commitments, that is, they imply that certain entities exist. For example, if the sentence "some electrons are bonded to protons" is true then it can be used to justify that electrons and protons exist. Quine used this insight to argue that one can learn about metaphysics by closely analyzing scientific claims to understand what kind of metaphysical picture of the world they presuppose.

In addition to methods of conducting metaphysical inquiry, there are various methodological principles used to decide between competing theories by comparing their theoretical virtues. Ockham's Razor is a well-known principle that gives preference to simple theories, in particular, to theories that assume that few entities exist. Other principles consider explanatory power, theoretical usefulness, and proximity to established beliefs.