In modal logic, the epistemic reading of the $5$ axiom scheme:

• • $♢\phi \to \square ♢\phi$

where $\square$ and $♢$ are necessity and possibility operators, respectively and $\to$ is a conditional connective. The negative introspection reading is more perpicuous when $5$ axiom is equivalently represented as:

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

When $\square$ is given an epistemic reading as a knowledge operator, this is equivalent to

• • if $\alpha$ does not know that $\phi$, then $\alpha$ knows that $\alpha$ does not know that $\phi$.

Negative introspection is generally regarded as implausible.