Epistemic logic has become a subfield of philosophical logic ever since the groundbreaking work by Hintikka (1962). Despite its various successful applications in philosophy, theoretical computer science, AI, and game theory, the technical developments of the field have been mainly focusing on the propositional part, i.e., the propositional modal logics of "knowing that". However, knowledge is expressed in everyday life by using various other expressions such as  "knowing what", "knowing how", "knowing why" and so on (knowing-wh hereafter). Such knowledge expressions are better captured in quantified epistemic logic, as was already discussed by Hintikka (1962) and sequel works at length. This talk aims to draw the attention back again to such a fascinating but largely neglected topic. After a brief survey on quantified epistemic logic, we propose a new quantifier-free approach to study the epistemic logics of knowing-wh, which may balance expressivity and complexity, and capture the essential reasoning patterns about knowing-wh. We survey our recent line of work on the epistemic logics of "knowing whether", "knowing what", "knowing how", and "knowing why" to demonstrate this new approach.
The talk is based on the survey paper with the same title to appear in Jaakko Hintikka on knowledge and game theoretical semantics, Springer (electronic version: http://arxiv.org/abs/1605.01995)