Reflective equilibrium is a coherence method of philosophical justification or inquiry. Nelson Goodman (1955) introduced reflective equilibrium, although not under that name, to contemporary philosophy in a discussion of deductive and inductive logic. It is arguable, however, that philosophers have employed something such as reflective equilibrium to inquire into a wide range of topics since ancient times.

Goodman maintained that we justify an inference by showing that it conforms to the rules of either deduction or induction. But for the inferences to be justified, these rules must be valid. Goodman held that we justify rules of inference by showing that they accord with judgments we make about which particular inferences are acceptable and which are unacceptable. Goodman addressed the obvious objection to such a procedure as follows:

This looks flagrantly circular. I have said that deductive inferences are justified by their conformity to valid general rules, and...