 Second, consider the claim that my mental states (or the mental subject itself) are as suited as objects in space to function as a reference whereby I can correctly judge the temporal order of my past experiences. Suppose I had available as such a reference only the mere mental appearance of a digital clock in one corner of my field of consciousness. This would not clearly be less effective than an actual clock in space. To this one might reply, with Dicker, that there are no actual mental states that are adequate to serve as such a reference. However, and this is the deeper worry, on Berkeley’s idealist view according to which the esse (to be) of objects in space is their percipi (to be perceived), any spatial objects would be nothing more than mental states of some subject, or aspects of those states, but Berkeleyan spatial perceptions would be as adequate a reference by which to determine the temporal order of my past experiences as perceptions of spatial objects that are in some sense distinct from my mental states (cf. Allison 1983: 300–1; Vogel 1993; Chignell 2010).