 Higher-order attitudes is a recurring theme in epistemic logic. The aforementioned Moore sentences, e.g., \(B_{a}(p\wedge B_{a}\neg p)\) express a higher-order attitude. So do many of the epistemic principles discussed in the literature and below. Consider the following prominent epistemic principle involving higher-order knowledge: \(K_{a}\varphi\rightarrow K_{a}K_{a}\varphi\). Is it reasonable to require that knowledge satisfies this scheme, i.e., that if somebody knows \(\varphi\), then they know that they know \(\varphi\)? In part, we might hesitate before accepting this principle in virtue of the higher-order attitude involved. This is a matter of ongoing discussion in epistemic logic and epistemology.