 In spite of these differences, given that the term ‘mental imagery’ was not systematically used until the end of the 19th century, throughout the history of philosophy people used the term ‘imagination’ to refer to what we now would describe as mental imagery. Thomas Hobbes, for example, talked about “retaining an image of the seen thing”, which comes very close to at least a subcategory of the current use of mental imagery in psychology and neuroscience, but he referred to this mental phenomenon as imagination (Hobbes 1651, Chapter 2). More generally, both the British empiricists and the German idealists used the term ‘imagination’ at least sometimes in the sense that would be captured by the concept of mental imagery nowadays (see Yolton 1996 for a summary). If we want to understand the evolution of philosophical thinking about mental imagery, we would need to go through all the historical texts about imagination and separate out references to voluntary acts (imagination proper) from references to mental imagery. This is not something that can be done in this encyclopedia entry.