 Broadly, there is agreement on the similarity between mental imagery and perception in phenomenology, which can be explicated as a similarity in content (Nanay 2016b; see, for example, Kind 2001; Nanay 2015; Noordhof 2002). Potential candidates for distinguishing mental imagery and perception include intensity (Hume’s Treatise of Human Nature; but see Kind 2017), voluntariness (McGinn 2004; Ichikawa 2009), causal relationship with the relevant object (Noordhof 2002); however, no consensus exists on features that clearly distinguish the two, in part because of ongoing debates about perception (see the entries on  contents of perception  and  epistemological problems of perception).