In modal logic, a thesis due to logician Oskar Becker (1889–1964) according to which the modal status of a formula $\phi$ is a necessary property. Put formally, where $♢$ and $\square$ symbolize possibility and necessity, respectively, Becker’s postulate is captured by the schema:

• • $♢\phi \to \square ♢\phi$

• • $\square \phi \to \square \square \phi$