A rule of inference in modal logics with a necessity operator $\square$ and conditional connective $\to$ named for logician Oskar Becker (1889–1964). The rule states that when $\square \left(\phi \to \psi \right)$ is a theorem, then the theoremhood of $\square \phi \to \square \psi$ may be inferred. Becker’s rule may be interpreted as a rule version of the axiom $\text{K}$.