There are several criteria commonly used to select the best scientific theory, including consistency, confirmation, and comprehensiveness. We discuss two criteria in particular:
(1) “Avoid metaphysics.” Modern science has a long history of avoiding metaphysics. Science was often contrasted with the wrangling of metaphysicians. While some metaphysical assumptions/presuppositions may be inevitable, a theory is preferred that has fewer metaphysical assumptions. “Don’t make metaphysical assumptions if possible, and if unavoidable, make them as benign as possible.” This incorporates “Occam’s razor” which says that entities should not be multiplied beyond necessity.
Naturalism or methodological naturalism is often considered a requirement for a scientific theory but the real requirement is the avoidance of metaphysics. Naturalism does avoid some metaphysical assumptions but it has its own metaphysical assumptions. A naturalistic theory should not be considered free of metaphysics, rather, its particular metaphysics should be considered along with everything else when selecting a theory.
(2) “Take the metaphysical middle way.” When the making of metaphysical assumptions cannot be avoided, a theory is preferred that has metaphysical assumptions in the middle of the range of metaphysical assumptions that have historically been employed. “Avoid metaphysical extremes.” Follow something like a golden mean or an intermediate metaphysical position.
Example: historical time
- An ancient and primitive conception of time is that it is cyclic, that history repeats. As the seasons and celestial positions repeat so does history. Cf. also Nietzsche’s Eternal Return.
- A modern and abstract conception of time is that of an open time line, that history is a linear sequence of events projected onto an open-ended geometric line. Such a line has no definite endpoints or is infinite. Relativistic time lines may be curved but the idea of an open-ended sequence remains.
- An intermediate conception is that historical time is a closed time line, with beginning and ending points. This is the Judeo-Christian conception of time. It is like the cyclic conception in that it consists of one cycle and in some ways the ending recapitulates the beginning. It is also like the time line conception in that it is a linear sequence of events.2007
- That which is “natural” conforms to these two principles. It has few metaphysical assumptions and what assumptions it has are middle-of-the-road so it is easy to accept.