Full Idea
In epistemic logic the knower is treated as logically omniscient. This is puzzling because one then cannot know something and yet fail to know that one knows it (the Principle of Positive Introspection).
Gist of Idea
In epistemic logic knowers are logically omniscient, so they know that they know
Source
M Fitting/R Mendelsohn (First-Order Modal Logic [1998], 1.11)
Book Reference
Fitting,M/Mendelsohn,R: 'First-Order Modal Logic' [Synthese 1998], p.28
A Reaction
This is nowadays known as the K-K Problem - to know, must you know that you know. Broadly, we find that externalists say you don't need to know that you know (so animals know things), but internalists say you do need to know that you know.