 There is relatively little philosophical research on procedural memory, and this kind of memory will not be discussed in any detail here. This should not, however, be taken to imply that it is not of major philosophical interest. In epistemological terms, while declarative memory maps onto the category of knowledge that, procedural memory maps onto the category of knowledge how: one may know or remember how to do something without consciously entertaining any relevant content and without being able, even in principle, to consciously entertain any such content. Future research on procedural memory might therefore build on classic (Ryle [1949] 2009) and contemporary (Stanley 2011) work on the relationship between knowledge that and knowledge how.